Unfortunately historical evidence on this point is almost wholly lacking. The differences in question could not have been appreciated at that remote period, and interest the common observer but little even today. The history of most of the cultivated plants is very obscure, [66] and even the most skillful historians, by sifting the evidence afforded by the older writers, and that obtained by comparative linguistic investigations have been able to do little more than frame the most general outline of the cultural history of the most common and most widely used plants.

Some authors assume that cultivation itself might have been the principal cause of variability, but it is not proved, nor even probable, that cultivated plants are intrinsically more variable than their wild prototypes. Appearances in this case are very deceptive. Of course widely distributed plants are as a rule richer in subspecies than forms with limited distribution, and the former must have had a better chance to be taken into cultivation than the latter. In many cases, especially with the more recent cultivated species, man has deliberately chosen variable forms, because of their greater promise. Thirdly, wide variability is the most efficient means of acclimatization, and only species with many elementary units would have offered the adequate material for introduction into new countries.

From this discussion it would seem that it is more reasonable to assert that variability is one of the causes of the success of cultivation, than to assume that cultivation is a cause of variability [67] at large. And this assumption would be equally sufficient to explain the existing conditions among cultivated plants.

Of course I do not pretend to say that cultivated plants should be expected to be less variable than in the wild state, or that swarms of elementary species might not be produced during cultivation quite as well as before. However the chance of such an event, as is easily seen, cannot be very great, and we shall have to be content with a few examples of which the coconut is a notable one.

Leaving this general discussion of the subject, we may take up the example of the beets. The sugar-beet is only one type from among a horde of others, and though the origin of all the single types is not historically known, the plant is frequently found in the wild state even at the present time, and the native types may be compared with the corresponding cultivated varieties.

The cultivation of beets for sugar is not of very ancient date. The Romans knew the beets and used them as vegetables, both the roots and the leaves. They distinguished a variety with white and one with red flesh, but whether they cultivated them, or only collected them from where they grew spontaneously, appears to be unknown.

[68] Beets are even now found in large quantities along the shores of Italy. They prefer the vicinity of the sea, as do so many other members of the beet family, and are not limited to Italy, but are found growing elsewhere on the littoral of the Mediterranean, in the Canary Islands and through Persia and Babylonia to India. In most of their native localities they occur in great abundance.

The color of the foliage and the size of the roots are extremely variable. Some have red leafstalks and veins, others a uniform red or green foliage, some have red or white or yellow roots, or exhibit alternating rings of a red and of a white tinge on cut surfaces. It seems only natural to consider the white and the red, and even the variegated types as distinct varieties, which in nature do not transgress their limits nor change into one another. In a subsequent lecture I will show that this at least is the rule with the corresponding color-varieties in other genera.

The fleshiness or pulpiness of the roots is still more variable. Some are as thick as the arm and edible, others are not thicker than a finger and of a woody composition, and the structure of this woody variety is very interesting. The sugar-beet consists, as is generally known, of concentric layers of sugar-tissue and of vascular [69] strands; the larger the first and the smaller the latter, the greater is, as a rule, the average amount of sugar of the race. Through the kindness of the late Mr. Rimpau, a well known German breeder of sugar-beet varieties, I obtained specimens from seed of a native wild locality near Bukharest. The plants produced quite woody roots, showing almost no sugar tissue at all. Woody layers of strongly developed fibrovascular strands were seen to be separated one from another only by very thin layers of parenchymatous cells. Even the number of layers is variable; it was observed to be five in my plants; but in larger roots double this number and even more may easily be met with.

Some authors have distinguished specific types among these wild forms. While the cultivated beets are collected under the head of Beta vulgaris, separate types with more or less woody roots have been described as Beta maritima and Beta patula. These show differences in the habit of the stems and the foliage. Some have a strong tendency to become annual, others to become biennial. The first of course do not store a large quantity of food in their roots, and remain thin, even at the time of flowering. The biennial types occur in all sizes of roots. In the annuals the stems may vary from [70] erect to ascending, and the name patula indicates stems which are densely branching from the base with widely spreading branches throughout. Mr. Em. von Proskowetz of Kwassitz, Austria, kindly sent me seeds of this Beta patula, the variability of which was so great in my cultures as to range from nearly typical sugar-beets to the thin woody type of Bukharest.

Broad and narrow leaves are considered to be differentiating marks between Beta vulgaris and Beta patula, but even here a wide range of forms seem to occur.

Rimpau, Proskowetz, Schindler and others have made cultures of beets from wild localities in order to discover a hypothetical common ancestor of all the present cultivated types. These researches point to the B. patula as the probable ancestor, but of course they were not made to decide the question as to whether the origination of the several now existing types had taken place before or during culture. From a general point of view the variability of the wild species is parallel to that of the cultivated forms to such a degree as to suggest the multiple origin of the former. But a close investigation of this highly important problem has still to be made.

The varieties of the cultivated beets are commonly [71] included in four subspecies. The two smallest are the salad-beets and the ornamental forms, the first being used as food, and ordinarily cultivated in red varieties, the second being used as ornamental plants during the fall, when they fill the beds left empty by summer flowers, with a bright foliage that is exceedingly rich in form and color. Of the remaining subspecies, one comprises the numerous sorts cultivated as forage-crops and the other the true sugar-beets. Both of them vary widely as to the shape and the size of the roots, the quality of the tissue, the foliage and other characteristics.

Some of these forms, no doubt, have originated during culture. Most of them have been improved by selection, and no beet found in the wild state ever rivals any cultivated variety. But the improvement chiefly affects the size, the amount of sugar and nutrient substances and some other qualities which recur in most of the varieties. The varietal attributes themselves however, are more or less of a specific nature, and have no relation to the real industrial value of the race. The short-rooted and the horn-shaped varieties might best be cited as examples.

The assertion that the sundry varieties of forage-beets are not the result of artificial selection, [72] is supported in a large measure by the historic fact that the most of them are far older than the method of conscious selection of plants itself. This method is due to Louis Vilmorin and dates from the middle of the last century. But in the sixteenth century most of our present varieties of beets were already in cultivation. Caspar Bauhin gives a list of the beets of his time and it is not difficult to recognize in it a large series of subspecies and varieties and even of special forms, which are still cultivated. A more complete list was published towards the close of the same century by Olivier de Serres in his world-renowned "Theatre d'Agriculture" (Paris, 1600).

The red forage-beets which are now cultivated on so large a scale, had been introduced from Italy into France only a short time before.

From this historic evidence, the period during which the beets were cultivated from the time of the Romans or perhaps much later, up to the time of Bauhin and De Serres, would seem far too short for the production by the unguided selection of man of all the now existing types. On the other hand, the parallelism between the characters of some wild and some cultivated varieties goes to make it very probable that other varieties have been found in the same way, some in this country and others in that, [73] and have been taken into cultivation separately. Afterwards of course all must have been improved in the direction required by the needs of man.

Quite the same conclusion is afforded by apples. The facts are to some extent of another character, and the rule of the derivation of the present cultivated varieties from original wild forms can be illustrated in this case in a more direct way. Of course we must limit ourselves to the varieties of pure ancestry and leave aside all those which are of hybrid or presumably hybrid origin.

Before considering their present state of culture, something must be, said about the earlier history and the wild state of the apples.

The apple-tree is a common shrub in woods throughout all parts of Europe, with the only exception of the extreme north. Its distribution extends to Anatolia, the Caucasus and Ghilan in Persia. It is found in nearly all forests of any extent and often in relatively large numbers of individuals. It exhibits varietal characters, which have led to the recognition of several spontaneous forms, especially in France and in Germany.

The differentiating qualities relate to the shape and indumentum of the leaves. Nothing is known botanically as to differences between [74] the fruits of these varieties, but as a matter of fact the wild apples of different countries are not at all the same.

Alphonse De Candolle, who made a profound study of the probable origin of most of our cultivated plants, comes to the conclusion that the apple tree must have had this wide distribution in prehistoric times, and that its cultivation began in ancient times everywhere.

This very important conclusion by so high an authority throws considerable light on the relation between cultivated and wild varieties at large. If the historic facts go to prove a multiple origin for the cultivation of some of the more important useful plants, the probability that different varieties or elementary species have been the starting points for different lines of culture, evidently becomes stronger.

Unfortunately, this historic evidence is scanty. The most interesting facts are those concerning the use of apples by the Romans and by their contemporaries of the Swiss and middle European lake-dwellings. Oswald Heer has collected large numbers of the relics of this prehistoric period. Apples were found in large quantities, ordinarily cut into halves and with the signs of having been dried. Heer distinguished two varieties, one with large and one with small fruits. The first about 3 and [75] the other about 1.5-2 cm. in diameter. Both are therefore very small compared with our present ordinary varieties, but of the same general size as the wild forms of the present day. Like these, they must have been of a more woody and less fleshy tissue. They would scarcely have been tasteful to us, but in ancient times no better varieties were known and therefore no comparison was possible.

There is no evidence concerning the question, as to whether during the periods mentioned apples were cultivated or only collected in the wild state. The very large numbers which are found, have induced some writers to believe in their culture, but then there is no reason why they should not have been collected in quantity from wild shrubs. The main fact is that the apple was not a uniform species in prehistoric times but showed even then at least some amount of variability.

At the present day the wild apples are very rich in elementary species. Those of Versailles are not the same as those of Belgium, and still others are growing in England and in Germany. The botanical differences derived from the blossoms and the leaves are slight, but the flavor, size and shape of the fruits diverge widely. Two opinions have been advanced to explain this high degree of variability, but [76] neither of them conveys a real explanation; their aim is chiefly to support different views as to the causes of variability, and the origin of elementary species at large.

One opinion, advocated by De Candolle, Darwin and others, claims that the varieties owe their origin to the direct influence of cultivation, and that the corresponding forms found in the wild state, are not at all original, but have escaped from cultivation and apparently become wild. Of course this possibility cannot be denied, at least in any single instance, but it seems too sweeping an assertion to make for the whole range of observed forms.

The alternative theory is that of van Mons, the Belgian originator of commercial varieties of apples, who has published his experiments in a large work called "Arbres fruitiers ou Pomonomie belge." Most of the more remarkable apples of the first half of the last century were produced by van Mons, but his greatest merit is not the direct production of a number of good varieties, but the foundation of the method, by which new varieties may be obtained and improved.

According to van Mons, the production of a new variety consists chiefly of two parts. The first is the discovery of a subspecies with new desirable qualities. The second is the transformation [77] of the original small and woody apple into a large, fleshy and palatable variety. Subspecies, or what we now call elementary species were not produced by man; nature alone creates new forms, as van Mons has it. He examined with great care the wild apples of his country, and especially those of the Ardennes, and found among them a number of species with different flavors. For the flavor is the one great point, which must be found ready in nature and which may be improved, but can never be created by artificial selection. The numerous differences in flavor are quite original; all of them may be found in the wild state and most of them even in so limited a region as the Ardennes Mountains. Of course van Mons preferred not to start from the wild types themselves, when the same flavor could be met with in some cultivated variety. His general method was, to search for a new flavor and to try to bring the bearer of it up to the desired standard of size and edibility.

The latter improvement, though it always makes the impression of an achievement, is only the last stone to be added to the building up of the commercial value of the variety. Without it, the best flavored apple remains a crab; with it, it becomes a conquest. According to the method of van Mons it may be reached within [78] two or three generations, and a man's life is wholly sufficient to produce in this way many new types of the very best sorts, as van Mons himself has done. It is done in the usual way, sowing on a large scale and selecting the best, which are in their turn brought to an early maturation of their fruit by grafting, because thereby the life from seed to seed may be reduced to a few years.

Form, taste, color, flavor and other valuable marks of new varieties are the products of nature, says van Mons, only texture, fleshiness and size are added by man. And this is done in each new variety by the same method and according to the same laws. The richness of the cultivated apples of the present day was already present in the large range of original wild elementary species, though unobserved and requiring improvement.

An interesting proof of this principle is afforded by the experience of Mr. Peter M. Gideon, as related by Bailey. Gideon sowed large quantities of apple-seeds, and one seed produced a new and valuable variety called by him the "Wealthy" apple. He first planted a bushel of apple-seeds, and then every year, for nine years, planted enough seeds to produce a thousand trees. At the end of ten years all seedlings had perished except one hardy seedling [79] crab. This experiment was made in Minnesota, and failed wholly. Then he bought a small lot of seeds of apples and crab-apples in Maine and from these the "Wealthy" came. There were only about fifty seeds in the lot of crab-apple seed which produced the "Wealthy," but before this variety was obtained, more than a bushel of seed had been sown. Chance afforded a species with an unknown taste; but the growing of many thousands of seedlings of known varieties was not the best means to get something really new.

Pears are more difficult to improve than apples. They often require six or more generations to be brought from the wild woody state to the ordinary edible condition. But the varieties each seem to have a separate origin, as with apples, and the wide range of form and of taste must have been present in the wild state, long before cultivation. Only recently has the improvement of cherries, plums, currants and gooseberries been undertaken with success by Mr. Burbank, and the difference between the wild and cultivated forms has hitherto been very small. All indications point to the existence, before the era of cultivation, of larger or smaller numbers of elementary species.

The same holds good with many of the larger forage crops and other plants of great industrial [80] value. Clover exhibits many varieties, which have been cultivated indiscriminately, and often in motley mixtures. The flower heads may be red or white, large or small, cylindric or rounded, the leaves are broader or narrower, with or without white spots of a curious pattern. They may be more or less hairy and so forth. Even the seeds exhibit differences in size, shape or color, and of late Martinet has shown, that by the simple means of picking out seeds of the same pattern, pure strains of clover may be obtained, which are of varying cultural value. In this way the best subspecies or varieties may be sought out for separate cultivation. Even the white spots on the leaflets have proved to be constant characters corresponding with noticeable differences in yield.

Flax is another instance. It was already cultivated, or at least made use of during the period of the lake-dwellers, but at that time it was a species referred to as Linum angustifolium, and not the Linum usitatissimum, which is our present day flax. There are now many subspecies, elementary species, and varieties under cultivation. The oldest of them is known as the "springing flax," in opposition to the ordinary "threshing flax." It has capsules which open of themselves, in order to disseminate the seeds, while the ordinary heads of the [81] flax remain closed until the seeds are liberated by threshing. It seems probable that the first form or Linum crepitans might thrive in the wild state as well as any other plant, while in the common species those qualities are lacking which are required for a normal dissemination of the seeds. White or blue flowers, high or dwarf stems, more or less branching at the base and sundry other qualities distinguish the varieties, aside from the special industrial difference of the fibres. Even the life-history varies from annual and biennial, to perennial.

It would take us too long to consider other instances. It is well known that corn, though considered as a single botanical species, is represented by different subspecies and varieties in nearly every region in which it is grown. Of course its history is unknown and it is impossible to decide whether all the tall and dwarf forms, or starchy and sweet varieties, dented or rounded kernels, and hundreds of others are older than culture or have come into existence during historic times, or as some assume, through the agency of man. But our main point now is not the origin, but only the existence of constant and sharply differentiated forms within botanical species. Nearly every cultivated plant affords instances of such diversity. Some include a few types only, while [82] others show, a large number of forms clearly separated to a greater or lesser degree.

In some few instances it is obvious that this variability is of later date than culture. The most conspicuous case is that of the coconut. This valuable palm is found on nearly all tropical coasts, in America, as well as in Asia, but in Africa and Australia there are many hundreds of miles of shore line, where it is not found. Its importance is not at all the same everywhere. On the shores and islands of the Indian Ocean and the Malay Archipelago, man is chiefly dependent upon it, but in America it is only of subordinate usefulness.

In connection with these facts, it abounds in subspecies and varieties in the East Indian regions, but on the continent of America little attention has as yet been given to its diverging qualities. In the Malayan region it affords nearly all that is required by the inhabitants. The value of its fruit as food, and the delicious beverage which it yields, are well known. The fibrous rind is not less useful; it is manufactured into a kind of cordage, mats and floor-cloths. An excellent oil is obtained from the kernel by compression. The hard covering of the stem is converted into drums and used in the construction of huts; the lower part is so hard as to take on a beautiful polish [83] when it resembles agate. Finally the unexpanded terminal bud is a delicate article of food. Many other uses could be mentioned, but these may suffice to indicate how closely the life of the inhabitants is bound up with the culture of this palm, and how sharply, in consequence, its qualities must have been watched by early man. Any divergence from the ordinary type must have been noted; those which were injurious must have been rejected, but the useful ones must have been appreciated and propagated. In a word any degree of variability afforded by nature must have been noticed and cultivated.

More than fifty different sorts of the coconut are described from the Indian shores and islands, with distinct local and botanical names. Miquel, who was one of the best systematists of tropical plants, of the last century, described a large number of them, and since, more have been added. Nearly all useful qualities vary in a higher or lesser degree in the different varieties. The fibrous strands of the rind of the nut are developed in some forms to such a length and strength as to yield the industrial product known as the coir-fibre. Only three of them are mentioned by Miquel that have this quality, the Cocos nucifera rutila, cupuliformis and stupposa. Among them the rutila [84] yields the best and most supple fibres, while those of the stupposa are stiff and almost unbending.

The varieties also differ greatly in size, color, shape and quality, and the trees have also peculiar characteristics. One variety exhibits leaves which are nearly entire, the divisions being only imperfectly separated, as often occurs in the very first leaves of the seedlings of other varieties. The flavor of the flesh, oil and milk likewise yield many good varietal marks.

In short, the coconut-palm comes under the general rule, that botanical species are built up of a number of sharply distinguishable types, which prove their constancy and relative independence by their wide distribution in culture. In systematic works all these forms are called varieties, and a closer investigation of their real systematic value has not yet been made. But the question as to the origin of the varieties and of the coconut itself has engrossed the attention of many botanists, among whom are De Candolle in the middle of the last century, and Cook at its close.

Both questions are closely connected. De Candolle claimed an Asiatic origin for the whole species, while Cook's studies go to prove that its original habitat is to be sought in the northern countries of South America. Numerous [85] varieties are growing in Asia and have as yet not been observed to occur in America, where the coconut is only of subordinate importance, being one of many useful plants, and not the only one relied upon by the natives for their subsistence. If therefore, De Candolle's opinion is the right one, the question as to whether the varieties are older or younger than the cultivated forms of the species, must always remain obscure. But if the proofs of an American origin should be forthcoming, the possibility, and even the probability that the varieties are of later date than the beginning of their culture, and have originated while in this condition must at once be granted. An important point in the controversy is the manner in which the coconuts were disseminated from shore to shore, from island to island. De Candolle, Darwin and most of the European writers claim that the dispersal was by natural agencies, such as ocean-currents. They point out that the fibrous rind or husk would keep the fruits afloat, and uninjured, for many days or even many weeks, while being carried from one country to another in a manner that would explain their geographic distribution. But the probability of the nuts being thrown upon the strand, and far enough from the shore to find suitable conditions for their germination, is a very small one. To insure [86] healthy and vigorous seedlings the nuts must be fully ripe, after which planting cannot be safely delayed for more than a few weeks. If kept too moist the nuts rot. If once on the shore, and allowed to lie in the sun, they become overheated and are thereby destroyed; if thrown in the shade of other shrubs and trees, the seedlings do not find the required conditions for a vigorous growth.

Some authors have taken the fibrous rind to be especially adapted to transport by sea, but if this were so, this would argue that water is the normal or at least the very frequent medium of dissemination, which of course it is not. We may, claim with quite as much right that the thick husk is necessary to enable the heavy fruit to drop from tall trees with safety. But even for this purpose the protection is not sufficient, as the nuts often suffer from falling to such a degree as to be badly injured as to their germinating qualities. It is well known that nuts, which are destined for propagation, are as a rule not allowed to fall off, but are taken from the trees with great care.

Summing up his arguments, Cook concludes that there is little in the way of known facts to support the poetic theory of the coconut palm dropping its fruits into the sea to float away to barren islands and prepare them for [87] human habitation. Shipwrecks might furnish a successful method of launching viable coconuts, and such have no doubt sometimes contributed to their distribution. But this assumption implies a dissemination of the nuts by man, and if this principal fact is granted, it is far more natural to believe in a conscious intelligent dissemination.

The coconut is a cultivated tree. It may be met with in some spots distant from human dwellings, but whenever such cases have been subjected to a closer scrutiny, it appears that evidently, or at least probably, huts had formerly existed in their neighborhood, but having been destroyed by some accident, had left the palm trees uninjured. Even in South America, where it may be found in forests at great distances from the sea-shore, it is not at all certain that true native localities occur, and it seems to be quite lost in its natural condition.

Granting the cultivated state of the palms as the only really important one, and considering the impossibility or at least great improbability of its dissemination by natural means, the distribution by man himself, according to his wants, assumes the rank of an hypothesis fully adequate to the explanation of all the facts concerning the life-history of the tree.

We now have to inquire into the main question, [88] whether it is probable that the coconut is of American or of Asiatic origin, leaving aside the historic evidence which goes to prove that nothing is known about the period in which its dissemination from one hemisphere to another took place, we will now consider only the botanic and geographic evidence, brought forward by Cook. He states that the whole family of coconut-palms, consisting of about 20 genera and 200 species, are all strictly American with the exception of the rather aberrant African oilpalm, which has, however, an American relative referred to the same genus. The coconut is the sole representative of this group which is connected with Asia and the Malayan region, but there is no manifest reason why other members of the same group could not have established themselves there, and maintained an existence under conditions, which are not at all unfavorable to them. The only obvious reason is the assumption already made, that the distribution was brought about by man, and thus only affected the species, chosen by him for cultivation. That the coconut cannot have been imported from Asia into America seems to be the most obvious conclusion from the arguments given. It should be briefly noted, that it was known and widely distributed in tropical America at the time of the discovery of that continent [89] by Columbus, according to accounts of Oviedo and other contemporary Spanish writers.

Concluding we may state that according to the whole evidence as it has been discussed by De Candolle and especially by Cook, the coconut-palm is of American origin and has been distributed as a cultivated tree by man through the whole of its wide range. This must have happened in a prehistoric era, thus affording time enough for the subsequent development of the fifty and more known varieties. But the possibility that at least some of them have originated before culture and have been deliberately chosen by man for distribution, of course remains unsettled.

Coconuts are not very well adapted for natural dispersal on land, and this would rather induce us to suppose an origin within the period of cultivation for the whole group. There are a large number of cultivated varieties of different species which by some peculiarity do not seem adapted for the conditions of life in the wild state. These last have often been used to prove the origin of varietal forms during culture. One of the oldest instances is the variety or rather subspecies of the opium-poppy, which lacks the ability to burst open its capsules. The seeds, which are thrown out by the wind, in the common forms, through the apertures underneath [90] the stigma, remain enclosed. This is manifestly a very useful adaptation for a cultivated plant, as by this means no seeds are lost. It would be quite a disadvantage for a wild species, and is therefore claimed to have been connected from the beginning with the cultivated form.

The large kernels of corn and grain, of beans and peas, and even of the lupines were considered by Darwin and others to be unable to cope with natural conditions of life. Many valuable fruits are quite sterile, or produce extremely few seeds. This is notoriously the case with some of the best pears and grapes, with the pine-apples, bananas, bread-fruits, pomegranate and some members of the orange tribe. It is open to discussion as to what may be the immediate cause of this sterility, but it is quite evident, that all such sterile varieties must have originated in a cultivated condition. Otherwise they would surely have been lost.

In horticulture and agriculture the fact that new varieties arise from time to time is beyond all doubt, and it is not this question with which we are now concerned. Our arguments were only intended to prove that cultivated species, as a rule, are derived from wild species, which obey the laws discussed in a previous lecture. The botanic units are compound entities, and [91] the real systematic units in elementary species play the same part as in ordinary wild species. The inference that the origin of the cultivated plants is multiple, in most cases, and that more than one, often many separate elementary forms of the same species must originally have been taken into cultivation, throws much light upon many highly important problems of cultivation and selection. This aspect of the question will therefore be the subject of the next lecture.

[92]

LECTURE IV

SELECTION OF ELEMENTARY SPECIES

The improvement of cultivated plants must obviously begin with already existing forms. This is true of old cultivated sorts as well as for recent introductions. In either case the starting-point is as important as the improvement, or rather the results depend in a far higher degree on the adequate choice of the initial material than on the methodical and careful treatment of the chosen varieties. This however, has not always been appreciated as it deserves, nor is its importance at present universally recognized. The method of selecting plants for the improvement of the race was discovered by Louis Vilmorin about the middle of the last century. Before his time selection was applied to domestic animals, but Vilmorin was the first to apply this principle to plants. As is well known, he used this method to increase the amount of sugar in beets and thus to raise their value as forage-crops, with such success, that his plants have since been used for the production [93] of sugar. He must have made some choice among the numerous available sorts of beets, or chance must have placed in his hands one of the most appropriate forms. On this point however, no evidence is at hand.

Since the work of Vilmorin the selection-principle has increased enormously in importance, for practical purposes as well as for the theoretical aspect of the subject. It is now being applied on a large scale to nearly all ornamental plants. It is the one great principle now in universal practice as well as one of preeminent scientific value. Of course, the main arguments of the evolution theory rest upon morphologic, systematic, geographic and paleontologic evidence. But the question as to how we can coordinate the relation between existing species and their supposed ancestors is of course one of a physiologic nature. Direct observation or experiments were not available for Darwin and so he found himself constrained to make use of the experience of breeders. This he did on a broad scale, and with such success that it was precisely this side of his arguments that played the major part in convincing his contemporaries.

The work of the breeders previous to Darwin's time had not been very critically performed. Recent analyses of the evidence obtained [94] from them show that numerous types of variability were usually thrown together. What type in each case afforded the material, which the breeder in reality made use of, has only been inquired into in the last few decades. Among those who have opened the way for thorough and more scientific treatment are to be mentioned Rimpau and Von Rumker of Germany and W.M. Hays of America.

Von Rumker is to be considered as the first writer, who sharply distinguished between two phases of methodical breeding-selection. One side he calls the production of new forms, the other the improvement of the breed. He dealt with both methods extensively. New forms are considered as spontaneous variations occurring or originating without human aid. They have only to be selected and isolated, and their progeny at once yields a constant and pure race. This race retains its character as long as it is protected against the admixture of other minor varieties, either by cross-pollination, or by accidental seeds.

Improvement, on the other hand, is the work of man. New varieties of course can only be isolated if chance offers them; the improvement is not incumbent on chance. It does not create really anything new, but develops characters, which were already existing. It brings [95] the race above its average, and must guard constantly against the regression towards this average which usually takes place.

Hays has repeatedly insisted upon the principle of the choice of the most favorable varieties as the foundation for all experiments in improving races. He asserts that half the battle is won by choosing the variety which is to serve as a foundation stock, while the other half depends upon the selection of parent-plants within the chosen variety. Thus the choice of the variety is the first principle to be applied in every single case; the so-called artificial selection takes only a secondary place. Calling all minor units within the botanic species by the common name of varieties, without regard to the distinction between elementary species and retrograde varieties, the principle is designated by the term of "variety-testing." This testing of varieties is now, as is universally known, one of the most important lines of work of the agricultural experiment stations. Every state and every region, in some instances even the larger farms, require a separate variety of corn, or wheat, or other crops. They must be segregated from among the hundreds of generally cultivated forms, within each single botanic species. Once found, the type may be ameliorated according to the local conditions [96] and needs, and this is a question of improvement.

The fact that our cultivated plants are commonly mixtures of different sorts, has not always been known. The first to recognize it seems to have been the Spanish professor of botany, Mariano Lagasca, who published a number of Spanish papers dealing with useful plants and botanical subjects between 1810 and 1830, among them a catalogue of plants cultivated in the Madrid Botanical Garden. Once when he was on a visit to Colonel Le Couteur on his farm in Jersey, one of the Channel Islands off the coast of France, in discussing the value of the fields of wheat, he pointed out to his host, that they were not really pure and uniform, as was thought at that time, and suggested the idea that some of the constituents might form a larger part in the harvest than others. In a single field he succeeded in distinguishing no less than 23 varieties, all growing together. Colonel Le Couteur took the hint, and saved the seeds of a single plant of each supposed variety separately. These he cultivated and multiplied till he got large lots of each and could compare their value. From among them he then chose the variety producing the greatest amount of the finest, whitest and most nutritious flour. This he eventually placed in the [97] market under the name of "Talavera de Bellevue." It is a tall, white variety, with long and slender white heads, almost without awns, and with fine white pointed kernels. It was introduced into commerce about 1830, and is still one of the most generally cultivated French wheats. It was highly prized in the magnificent collection of drawings and descriptions of wheats, published by Vilmorin under the title "Les meilleurs bles" and is said to have quite a number of valuable qualities, branching freely and producing an abundance of good grain and straw. It is however, sensitive to cold winters in some degree and thereby limited in its distribution. Hallett, the celebrated English wheat-breeder, tried in vain to improve the peculiar qualities of this valuable production of Le Couteur's.

Le Couteur worked during many years along this line, long before the time when Vilmorin conceived the idea of improvement by race selections, and he used only the simple principle of distinguishing and isolating the members of his different fields. Later he published his results in a work on the varieties, peculiarities and classification of wheat (1843), which though now very rare, has been the basis and origin of the principle of variety-testing.

The discovery of Lagasca and Le Couteur was [98] of course not applicable to the wheat of Jersey alone. The common cultivated sorts of wheat and other grains were mixtures then as they are even now. Improved varieties are, or at least should be, in most cases pure and uniform, but ordinary sorts, as a rule, are mixtures. Wheat, barley and oats are self-fertile and do not mix in the field through cross-pollination. Every member of the assemblage propagates itself, and is only checked by its own greater or less adaptation to the given conditions of life. Rimpau has dealt at large with the phenomenon as it occurs in the northern and middle parts of Germany. Even Rivett's "Bearded wheat," which was introduced from England as a fine improved variety, and has become widely distributed throughout Germany, cannot keep itself pure. It is found mingled almost anywhere with the old local varieties, which it was destined to supplant. Any lot of seed exhibits such impurities, as I have had the opportunity of observing myself in sowings in the experimental-garden. But the impurities are only mixtures, and all the plants of Rivett's "Bearded wheat," which of course constitute the large majority, are of pure blood. This may be confirmed when the seeds are collected and sown separately in cultures that can be carefully guarded.

[99] In order to get a closer insight into the causes of this confused condition of ordinary races, Rimpau made some observations on Rivett's wheat. He found that it suffers from frost during winter more than the local German varieties, and that from various causes, alien seeds may accidentally, and not rarely, become mixed with it. The threshing-machines are not always as clean as they should be and may be the cause of an accidental mixture. The manure comes from stables, where straw and the dust from many varieties are thrown together, and consequently living kernels may become mixed with the dung. Such stray grains will easily germinate in the fields, where they find more congenial conditions than does the improved variety. If winter arrives and kills quantities of this latter, the accidental local races will find ample space to develop. Once started, they will be able to multiply so rapidly, that in one or two following generations they will constitute a very considerable portion of the whole harvest. In this way the awnless German wheat often prevails over the introduced English variety, if the latter is not kept pure by continuous selection.

The Swiss wheat-breeder Risler made an experiment which goes to prove the certainty of the explanation given by Rimpau. He observed on his farm at Saleves near the lake of Geneva that after a lapse of time the "Galland wheat" deteriorated and assumed, as was generally believed, the characters of the local sorts. In order to ascertain the real cause of this apparent change, he sowed in alternate rows in a field, the "Galland" and one of the local varieties. The "Galland" is a race with obvious characters and was easily distinguished from the other at the time when the heads were ripe. They are bearded when flowering, but afterwards throw off the awns. The kernels are very large and yield an extraordinarily good, white flour.

During the first summer all the heads of the "Galland" rows had the deciduous awns but the following year these were only seen on half of the plants, the remainder having smooth heads, and the third year the "Galland" had nearly disappeared, being supplanted by the competing local race. The cause of this rapid change was found to be twofold. First the "Galland," as an improved variety, suffers from the winter in a far higher degree than the native Swiss sorts, and secondly it ripens its kernels one or two weeks later. At the time of harvest it may not have become fully ripe, while the varieties mixed with it had reached maturity. The wild oat, Avena fatua, is very common in [101] Europe from whence it has been introduced in the United States. In summers which are unfavorable to the development of the cultivated oats it may be observed to multiply with an almost incredible rapidity. It does not contribute to the harvest, and is quite useless. If no selection were made, or if selection were discontinued, it would readily supplant the cultivated varieties.

From these several observations and experiments it may be seen, that it is not at all easy to keep the common varieties of cereals pure and that even the best are subject to the encroachment of impurities. Hence it is only natural that races of cereals, when cultivated without the utmost care, or even when selected without an exact knowledge of their single constituents, are always observed to be more or less in a mixed condition. Here, as everywhere with cultivated and wild plants, the systematic species consist of a number of minor types, which pertain to different countries and climates, and are growing together in the same climate and under the same external conditions. They do not mingle, nor are their differentiating characters destroyed by intercrossing. They each remain pure, and may be isolated whenever and wherever the desirability for such a proceeding should arise. The purity of [102] the races is a condition implanted in them by man, and nature always strives against this arbitrary and one-sided improvement. Numerous slight differences in characters and numerous external influences benefit the minor types and bring them into competition with the better ones. Sometimes they tend to supplant the latter wholly, but ordinarily sooner or later a state of equilibrium is reached, in which henceforth the different sorts may live together. Some are favored by warm and others by cool summers, some are injured by hard winters while others thrive then and are therefore relatively at an advantage. The mixed condition is the rule, purity is the exception.

Different sorts of cereals are not always easily distinguishable by the layman and therefore I will draw your attention to conditions in meadows, where a corresponding phenomenon can be observed in a much simpler way.

Only artificial pasture-grounds are seen to consist of a single species of grass or clover. The natural condition in meadows is the occurrence of clumps of grasses and some clovers, mixed up with perhaps twenty or more species of other genera and families. The numerical proportion of these constituents is of great interest, and has been studied at Rothamstead in England and on a number of other farms. It is [103] always changing. No two successive years show exactly the same proportions. At one time one species prevails, at another time one or two or more other species. The weather during the spring and summer benefits some and hurts others, the winter may be too cold for some, but again harmless for others, the rainfall may partly drown some species, while others remain uninjured. Some weeds may be seen flowering profusely during some years, while in other summers they are scarcely to be found in the same meadow. The whole population is in a fluctuating state, some thriving and others deteriorating. It is a continuous response to the ever changing conditions of the weather. Rarely a species is wholly annihilated, though it may apparently be so for years; but either from seeds or from rootstocks, or even from neighboring lands, it may sooner or later regain its foothold in the general struggle for life.

This phenomenon is a very curious and interesting one. The struggle for life, which plays so considerable a part in the modern theories of evolution, may be seen directly at work. It does not alter the species themselves, as is commonly supposed, but it is always changing their numerical proportion. Any lasting change in the external conditions will of course alter the average oscillation and the influence [104] of such alterations will manifest itself in most cases simply in new numerical proportions. Only extremes have extreme effects, and the chance for the weaker sorts to be completely overthrown is therefore very small.

Any one, who has the opportunity of observing a waste field during a series of years, should make notes concerning the numerical proportions of its inhabitants. Exact figures are not at all required; approximate estimates will ordinarily prove to be sufficient, if only the standard remains the same during the succeeding years.

The entire mass of historic evidence goes to prove that the same conditions have always prevailed, from the very beginning of cultivation up to the present time. The origin of the cultivation of cereals is to be sought in central Asia. The recent researches of Solms Laubach show it to be highly probable that the historic origin of the wheat cultivated in China, is the same as that of the wheat of Egypt and Europe. Remains of cereals are found in the graves of Egyptian mummies, in the mounds of waste material of the lake-dwellings of Central Europe, and figures of cereals are to be seen on old Roman coins. In the sepulchre of King Ra-n-Woser of the Fifth Dynasty of Egypt, who lived about 2000 years B.C., two [105] tombs have recently been opened by the German Oriental Society. In them were found quantities of the tares of the Triticum dicoccum, one of the more primitive forms of wheat. In other temples and pyramids and among the stones of the walls of Dashur and El Kab studied by Unger, different species and varieties of cereals were discovered in large quantities, that showed their identity with the present prevailing cultivated races of Egypt.

The inhabitants of the lake-dwellings in Switzerland possessed some varieties of cereals, which have entirely disappeared. They are distinguished by Heer under special names. The small barley and the small wheat of the lake-dwellers are among them. All in all there were ten well distinguished varieties of cereals, the Panicum and the Setaria or millet being of the number. Oats were evidently introduced only toward the very last of the lake-dwelling period, and rye is of far later introduction into western Europe. Similar results are attained by the examination of the cereals figured by the Romans of the same period.

All these are archaeologic facts, and give but slight indications concerning the methods of cultivation or the real condition of the cultivated races of that time. Virgil has left us some knowledge of the requirements of methodical [106] culture of cereals of his time. In his poem Georgics (I. 197) the following lines are found:

Vidi lecta din, et multo spectata labore Degenerare tamen, ni vis humana quotannis Maxima quaeque manu legeret.

(The chosen seed, through years and labor improved, Was seen to run back, unless yearly Man selected by hand the largest and fullest of ears.)

Elsewhere Virgil and also some lines of Columella and Varro go to prove in the same way that selection was applied by the Romans to their cereals, and that it was absolutely necessary to keep their races pure. There is little doubt, but that it was the same principle as that which has led, after many centuries, to the complete isolation and improvement of the very best races of the mixed varieties. It further proves that the mixed conditions of the cereals was known to man at that time, although distinct ideas of specific marks and differences were of course still wholly lacking. It is proof also that cultivated cereals from the earliest times must have been built up of numerous elementary forms. Moreover it is very probable, that in the lapse of centuries a goodly number of such types must have disappeared. [107] Among the vanished forms are the special barley and wheat of the lake-dwellings, the remains of which have been accidentally preserved, but most of the forms must have disappeared without leaving any trace.

This inference is supported by the researches of Solms-Laubach, who found that in Abyssinia numerous primitive types of cereals are still in culture. They are not adequate to compete with our present varieties, and would no doubt also have disappeared, had they not been preserved by such quite accidental and almost primitive isolation.

Closing this somewhat long digression into history we will now resume our discussion concerning the origin of the method of selecting cereals for isolation and segregate-cultivation. Some decades after Le Couteur, this method was taken up by the celebrated breeder Patrick Sheriff of Haddington in Scotland. His belief, which was general at that time, was "That cultivation has not been found to change well defined kinds, and that improvement can be best attained by selecting new and superior varieties, which nature occasionally produces, as if inviting the husbandman to stretch forth his hand and cultivate them."

Before going into the details of Sheriff's work it is as well to say something concerning [108] the use of the word "selection." This word was used by Sheriff as seen in the quotation given, and it was obviously designed to convey the same idea as the word "lecta" in the quotation from Virgil. It was a choice of the best plants from among known mixed fields, but the chosen individuals were considered to be representatives of pure and constant races, which could only be isolated, but not ameliorated. Selection therefore, in the primitive sense of the word, is the choice of elementary species and varieties, with no other purpose than that of keeping them as pure as possible from the admixture of minor sorts. The Romans attained this end only imperfectly, simply because the laws governing the struggle for life and the competition of numerous sorts in the fields were unsuspected by them.

Le Couteur and Sheriff succeeded in the solution of the problem, because they had discovered the importance of isolation. The combination of a careful choice with subsequent isolation was all they knew about it, and it was one of the great achievements to which modern agriculture owes its success.

The other great principle was that of Vilmorin. It was the improvement within the race, or the "amelioration of the race" as it was termed by him. It was introduced into [109] England by F.F. Hallett of Brighton in Sussex, who at once called it "pedigree-culture," and produced his first new variety under the very name of "Pedigree-wheat." This principle, which yields improved strains, that are not constant but dependent on the continued and careful choice of the best plants in each succeeding generation, is now generally called "selection." But it should always be remembered that according to the historic evolution of the idea, the word has the double significance of the distinction and isolation of constant races from mixtures, and that of the choice of the best representatives of a race during all the years of its existence. Even sugar-beets, the oldest "selected" agricultural plants, are far from having freed themselves from the necessity of continuous improvement. Without this they would not remain constant, but would retrograde with great rapidity.

The double meaning of the word selection still prevailed when Darwin published his "Origin of Species." This was in the year 1859, and at that time Shirreff was the highest authority and the most successful breeder of cereals. Vilmorin's method had been applied only to beets, and Hallett had commenced his pedigree-cultures only a few years before and his first publication of the "Pedigree-wheat" [110] appeared some years later at the International Exhibition of London in 1862. Hence, whenever Darwin speaks of selection, Shirreff's use of the word may as well be meant as that of Vilmorin.

However, before going deeper into such theoretical questions, we will first consider the facts, as given by Shirreff himself.

During the best part of his life, in fact during the largest part of the first half of the nineteenth century, Shirreff worked according to a very simple principle. When quite young he had noticed that sometimes single plants having better qualities than the average were seen in the fields. He saved the grains, or sometimes the whole heads of such plants separately, and tried to multiply them in such manner as to avoid intermixtures.

His first result was the "Mungoswell's wheat." In the spring of 1819 he observed quite accidentally in a field of the farm of that name, a single plant which attracted his attention by a deeper green and by being more heavily headed out. Without going into further details, he at once chose this specimen as the starting point of a new race. He destroyed the surrounding plants so as to give it more space, applied manure to its roots, and tended it with special care. It yielded 63 heads and nearly [111] 2500 grains. All of these were sown the following fall, and likewise in the succeeding years the whole harvest was sown in separate lots. After two years of rapid multiplication it proved to be a good new variety and was brought into commerce. It has become one of the prominent varieties of wheat in East Lothian, that county of Scotland of which Haddington is the principal borough.

The grains of "Mungoswell's wheat" are whiter than those of the allied "Hunter's wheat," more rounded but otherwise of the same size acid weight. The straw is taller and stronger, and each plant produces more culms and more heads.

Shirreff assumed, that the original plant of this variety was a sport from the race in which he had found it, and that it was the only instance of this sport. He gives no details about this most interesting side of the question, omitting even to tell the name of the parent variety. He only asserts that it was seen to be better, and afterwards proved so by the appreciation of other breeders and its success in trade. He observed it to be quite constant from the beginning, no subsequent selection being needed. This important feature was simply assumed by him to be true as a matter of course.

[112] Some years afterwards, in the summer of 1824, he observed a large specimen of oats in one of the fields of the same farm. Being at that time occupied in making a standard collection of oats for a closer comparison of the varieties, he saved the seeds of that plant and sowed them in a row in his experiment-field. It yielded the largest culms of the whole collection and bore long and heavy kernels with a red streak on the concave side and it excelled all other sorts by the fine qualities of its very white meal. In the unequal length of its stalks it has however a drawback, as the field appears thinner and more meager than it is in reality. "Hopetown oats," as it is called, has found its way into culture extensively in Scotland and has even been introduced with success into England, Denmark and the United States. It has been one of the best Scottish oats for more than half a century.

The next eight years no single plant judged worthy of selection on his own farm attracted Shirreff's attention. But in the fall of 1832 he saw a beautiful plant of wheat on a neighboring farm and he secured a head of it with about 100 grains. From this he produced the "Hopetown wheat." After careful separation from the kernels this original ear was preserved, and was afterwards exhibited at the Stirling Agricultural [113] Museum. The "Hopetown wheat" has proved to be a constant variety, excelling the ordinary "Hunter's wheat" by larger grains and longer heads; it yields likewise a straw of superior quality and has become quite popular in large districts of England and Scotland, where it is known by the name of "White Hunter's" from its origin and the brilliant whiteness of its heads.

In the same way Shirreff's oats were discovered in a single plant in a field where it was isolated in order to be brought into commerce after multiplication. It has won the surname of "Make-him-rich." Nothing is on record about the details of its origin.

Four valuable new varieties of wheat and oats were obtained in this way in less than forty years. Then Shirreff changed his ideas and his method of working. Striking specimens appeared to be too rare, and the expectation of a profitable result too small. Therefore he began work on a larger scale. He sought and selected during the summer of 1857 seventy heads of wheat, each from a single plant showing some marked and presumably favorable peculiarity. These were not gathered on one field, but were brought together from all the fields to which he had access in his vicinity. The grains of each of these selected heads were [114] sown separately, and the lots compared during their whole life-period and chiefly at harvest time. Three of the lots were judged of high excellence, and they alone were propagated, and proving to be constant new varieties from the outset were given to the trade under the names of "Shirreff's bearded white," "Shirreff's bearded red," and "Pringle's wheat." They have found wide acceptance, and the first two of them are still considered by Vilmorin as belonging to the best wheats of France.

This second method of Shirreff evidently is quite analogous to the principle of Lagasca and Le Couteur. The previous assumption that new varieties with striking features were being produced by nature from time to time, was abandoned, and a systematic inquiry into the worth of all the divergent constituents of the fields was begun. Every single ear at once proved to belong to a constant and pure race, but most of these were only of average value. Some few however, excelled to a degree, which made them worth multiplying, and to be introduced into trade as separate varieties.

Once started, this new method of comparison, selection and isolated multiplication was of course capable of many improvements. The culture in the experiment-field was improved, so as to insure a fuller and more rapid growth.

[115] The ripe heads had to be measured and counted and compared with respect to their size and the number of their kernels. Qualities of grain and of meal had to be considered, and the influence of climate and soil could not be overlooked.

Concerning the real origin of his new types Shirreff seems never to have been very inquisitive. He remarks that only the best cultivated varieties have a chance to yield still better types, and that it is useless to select and sow the best heads of minor sorts. He further remarks that it is not probable that he found a new sport every time; on the contrary he assumes that his selections had been present in the field before, and during a series of succeeding generations. How many years old they were, was of course impossible to determine. But there is no reason to believe that the conditions in the fields of Scotland were different from those observed on the Isle of Jersey by Le Couteur.

In the year 1862 Shirreff devoted himself to the selection of oats, searching for the best panicles from the whole country, and comparing their offspring in his experimental garden. "Early Fellow," "Fine Fellow," "Longfellow" and "Early Angus" are very notable varieties introduced into trade in this way.

[116] Some years later Patrick Shirreff described his experiments and results in a paper entitled, "On the improvement of cereals," but the descriptions are very short, and give few details of systematic value. The leading principle, however, is clearly indicated, and anyone who studies with care his method of working, may confidently attempt to improve the varieties of his own locality in the same way.

This great principle of "variety-testing," as it has been founded by Le Couteur and Patrick Shirreff, has increased in importance ever since. Two main features are to be considered here. One is the production of local races, the other the choice of the best starting-point for hybridizing experiments, as is shown in California by the work of Luther Burbank in crossing different elementary species of Lilium pardalinum and others.

Every region and locality has its own conditions of climate and soil. Any ordinary mixed race will contain some elementary forms which are better adapted to a given district, while others are more suitable to divergent conditions. Hence it can readily be inferred that the choice cannot be the same for different regions. Every region should select its own type from among the various forms, and variety testing therefore becomes a task which every [117] one must undertake under his own conditions. Some varieties will prove, after isolation, to be profitable for large districts and perhaps for whole states. Others will be found to be of more local value, but in such localities to excel all others.

As an example we may take one of the varieties of wheat originated by the Minnesota Experiment Station. Hays described it as follows. It was originated from a single plant. From among 400 plants of "Blue stem" several of the best were chosen, each growing separately, a foot apart in every direction. Each of the selected plants yielded 500 or more grains of wheat, weighing 10 or more grams. The seeds from these selected plants were raised for a few years until sufficient was obtained to sow a plot. Then for several years the new strains were grown in a field beside the parent-variety. One of them was so much superior that all others were discarded. It was the one named "Minnesota No. 169." For a large area of Minnesota this wheat seems capable of yielding at least 1 or 2 bushels more grain per acre than its parent variety, which is the best kind commonly and almost universally found on the farms in southern and central Minnesota.

It would be quite superfluous for our present purpose to give more instances. The fact of [118] the compound nature of so-called species of cultivated plants seems to be beyond all doubt, and its practical importance is quite obvious.

Acclimatization is another process, which is largely dependent on the choice of adequate varieties. This is shown on a large scale by the slow and gradual dispersion of the varieties of corn in this country. The largest types are limited to temperate and subtropical regions, while the varieties capable of cultivation in more northern latitudes are smaller in size and stature and require a smaller number of days to reach their full development from seed to seed. Northern varieties are small and short lived, but the "Forty-day-corn" or "Quarantino maize" is recorded to have existed in tropical America at the time of Columbus. In preference, or rather to the entire exclusion of taller varieties, it has thriven on the northern boundaries of the corn-growing states of Europe since the very beginning of its cultivation.

According to Naudin, the same rule prevails with melons, cucumbers and gherkins, and other instances could easily be given.

Referring now to the inferences that may be drawn from the experience of the breeders in order to elucidate the natural processes, we will return to the whitlow-grasses and pansies.

[119] Nature has constituted them as groups of slightly different constant forms, quite in the same way as wheat and oats and corn. Assuming that this happened ages ago somewhere in central Europe, it is of course probable that the same differences in respect to the influence of climatic conditions will have prevailed as with cereals. Subsequent to the period which has produced the numerous elementary species of the whitlow-grass came a period of widespread distribution. The process must have been wholly comparable with that of acclimatization. Some species must have been more adapted to northern climates, others to the soils of western or eastern regions and so on. These qualities must have decided the general lines of the distribution, and the species must have been segregated according to their respective climatic qualities, and their adaptability to soil and weather. A struggle for life and a natural selection must have accompanied and guided the distribution, but there is no reason to assume that the various forms were changed by this process, and that we see them now endowed with other qualities than they had at the outset.

Natural selection must have played, in this and in a large number of other cases, quite the same part as the artificial method of variety testing.

[120] Indeed it may be surmised that this has been its chief and prominent function. Taking up again our metaphor of the sieve we can assert that in such cases climate and soil exercise sifting action and in this way the application of the metaphor becomes more definite. Of course, next to the climate and soil in importance, come ecological conditions, the vegetable and animal enemies of the plants and other influences of the same nature.

In conclusion it is to be pointed out that this side of the problem of natural selection and the struggle for life appears to offer the best prospects for experimental, or for continued statistical inquiry. Direct observations are possible and any comparison of numerical proportions of species in succeeding years affords clear proof of the part it plays. And above all, such observations can be made quite independently of doubtful theoretical considerations about presumed changes of character.

The fact of natural selection is plain and it should be studied in its most simple conditions.

[121] C. RETROGRADE VARIETIES

LECTURE V

CHARACTERS OF RETROGRADE VARIETIES

Every one admires the luxuriance of garden-flowers, and their diversity of color and form. All parts of the world have contributed to their number and every taste can find its preference among them. New forms produced by the skill of the breeder are introduced every year. This has been done mostly by crossing and intermingling the characters of introduced species of the same genus. In some of the cases the history of our flowers is so old that their hybrid origin is forgotten, as in the case of the pansies. Hybridizations are still going on in other groups on a large scale, and new forms are openly claimed to be of hybrid origin.

Breeders and amateurs generally have more interest in the results than in the way in which they have been brought about. Excellent flowers and fruit recommend themselves and there seems to be no reason for inquiring [122] about their origin. In some cases the name of the originator may be so widely known that it adds weight to the value of the new form, and therefore may advantageously be coupled with it. The origin and history of the greater part of our garden-flowers, fruits and vegetables are obscure; we see them as they are, and do not know from whence they came. The original habitat for a whole genus or for a species at large, may be known, but questions as to the origin of the single forms, of which it is built up, ordinarily remain unanswered.

For these reasons we are restricted in most cases to the comparison of the forms before us. This comparison has led to the general use of the term "variety" in opposition to "species." The larger groups of forms, which are known to have been introduced as such are called species. All forms which by their characters belong to such a species are designated as varieties, irrespective of their systematic relation to the form, considered as the ancestor of the group.

Hence, we distinguish between "hybrid varieties" and "pure varieties" according to their origin from different parents or from a single line of ancestors. Moreover, in both groups the forms may be propagated by seeds, or in the vegetative way by buds, by grafting or [123] by cutting, and this leads to the distinction of "seed-varieties" and "vegetative varieties." In the first case the inheritance of the special characters through the seeds decides the status of the variety, in the latter case this point is left wholly out of consideration.

Leaving aside all these different types, we are concerned here only with the "seed-varieties" of pure origin, or at least with those, that are supposed to be so. Hybridization and vegetative multiplication of the hybrids no doubt occur in nature, but they are very rare, when compared with the ordinary method of propagation by seed. "Seed-varieties" may further be divided into constant and inconstant ones. The difference is very essential, but the test is not always easy to apply. Constant varieties are as sharply defined and as narrowly limited as are the best wild species, while inconstant types are cultivated chiefly on account of their wide range of form and color. This diversity is repeated yearly, even from the purest seed. We will now discuss the constant seed-varieties, leaving the inconstant and eversporting types to a subsequent lecture.

In this way we may make an exact inquiry into the departures from the species which are ordinarily considered to constitute the essential character of such a constant and pure seed-variety [124] and need only compare these differences with those that distinguish the elementary species of one and the same group from each other.

Two points are very striking. By far the greatest part of the ordinary garden-varieties differ from their species by a single sharp character only. In derivative cases two, three or even more such characters may be combined in one variety, for instance, a dwarfed variety of the larkspur may at the same time bear white flowers, or even double white flowers, but the individuality of the single characters is not in the least obscured by such combinations.

The second point is the almost general occurrence of the same variety in extended series of species. White and double flowers, variegated leaves, dwarfs and many other instances may be cited. It is precisely this universal repetition of the same character that strikes us as the essential feature of a variety.

And again these two characteristics may now be considered separately. Let us begin with the sharpness of the varietal characters. In this respect varieties differ most obviously from elementary species. These are distinguished from their nearest allies in almost all organs. There is no prominent distinctive feature between the single forms of Draba [125] Verna, Helianthemum or of Taraxacum; all characters are almost equally concerned. The elementary species of Draba are characterized, as we have seen, by the forms and the hairiness of the leaves, the number and height of the flower-stalks, the breadth and incision of the petals, the forms of the fruits, and so on. Every one of the two hundred forms included in this collective species has its own type, which it is impossible to express by a single term. Their names are chosen arbitrarily. Quite the contrary is the case with most of the varieties, for which one word ordinarily suffices to express the whole difference.

White varieties of species with red or blue flowers are the most common instances. If the species has a compound color and if only one of the constituents is lost, partially colored types arise as in _Agrostemma Coronaria bicolor_. Or the spots may disappear and the color become uniform as in _Gentiana punctata concolor_ and the spotless Arum or _Arum maculatum immaculatum_. Absence of hairs produces forms as _Biscutella laevigata glabra_; lack of prickles gives the varieties known as _inermis, as for instance, _Ranunculus arvensis inermis_. _Cytisus prostratus_ has a variety _ciliata_, and _Solanum Dulcamara_, or the bitter-sweet, has a variety called _tomentosum_. The curious monophyllous [126] variety of the strawberry and many other forms will be discussed later.

To enlarge this list it would only be necessary to extract from a flora, or from a catalogue of horticultural plants, the names of the varieties enumerated therein. In nearly every instance, where true varieties and not elementary species are concerned, a single term expresses the whole character.

Such a list would also serve to illustrate the second point since the same names would recur frequently. Long lists of varieties are called alba, or inermis, or canescens or lutea, and many genera contain the same appellations. In some instances the systematists use a diversity of names to convey exactly the same idea, as if to conceal the monotony of the character, as for instance in the case of the lack of hairs, which is expressed by the varietal names of Papaver dubium glabrum, Arabis ciliata glabrata, Arabis hirsuta glaberrima, Veronica spicata nitens, Amygdalus persica laevis, Paeonia corallina Leiocarpa, &c.

On the contrary we find elementary species in different genera based on the greatest possible diversity of features. The forms of Taraxacum or Helianthemum do not repeat those of Draba or Viola. In roses and brambles the distinguishing features are characteristic of the type, as [127] they are evidently derived from it and limited to it. And this is so true that nobody claims the grade of elementary species for white roses or white brambles, but everyone recognizes that forms diverging from the nearest species by a single character only, are to be regarded as varieties.

This general conviction is the basis on which we may build up a more sharply defined distinction between elementary species and varieties. It is an old rule in systematic botany, that no form is to be constituted a species upon the basis of a single character. All authors agree on this point; specific differences are derived from the totality of the attributes, not from one organ or one quality. This rule is intimately connected with the idea that varieties are derived from species. The species is the typical, really existing form from which the variety has originated by a definite change. In enumerating the different forms the species is distinguished by the term of genuine or typical, often only indicated as a or the first; then follow the varieties sometimes in order of their degree of difference, sometimes simply in alphabetical order. In the case of elementary species there is no real type; no one of them predominates because all are considered to be equal in rank, and the systematic species to which they [128] are referred is not a really existing form, but is the abstraction of the common type of all, just as it is in the case of a genus or of a family.

Summarizing the main points of this discussion, we find that elementary species are of equal rank and together build up the collective or systematic ideal species. Varieties on the other hand are derived from a real and commonly, still existing type.

I hope that I have succeeded in showing that the difference between elementary species, or, as they are often called, smaller or subspecies, on the one hand and varieties on the other, is quite a marked one. However, in order to recognize this principle it is necessary to limit the term variety, to those propagating themselves by seed and are of pure and not of hybrid origin.

But the principle as stated here, does not involve an absolute contrast between two groups of characters. It is more a difference in our knowledge and appreciation of them than a difference in the things themselves. The characters of elementary species are, as a rule, new to us, while those of varieties are old and familiar. It seems to me that this is the essential point.

And what is it that makes us familiar with them? Obviously the continuous recurrence of the same changes, because by a constant repetition they must of course lose their novelty.

[129] Presently we shall look into these characters more in detail and then we shall find that they are not so simple as might be supposed at first sight; but precisely because we are so familiar with them, we readily see that their different features really belong to a single character; while in elementary species everything is so new that it is impossible for us to discern the unities of the new attributes.

If we bear in mind all these difficulties we cannot wonder at the confusion on this question that seems to prevail everywhere. Some authors following Linnaeus simply call all the subdivisions of species, varieties; others follow Jordan and avoid the difficulty by designating all smaller forms directly as species. The ablest systematists prefer to consider the ordinary species as collective groups, calling their constituents "The elements of the species," as was done by A.P. De Candolle, Alph. De Candolle and Lindley.

By this method they clearly point out the difference between the subdivisions of wild species as they ordinarily occur, and the varieties in our gardens, which would be very rare, were they not singled out and preserved.

Our familiarity with a character and our grounds for calling it an old acquaintance may result from two causes, which in judging a new [130] variety are essentially different. The character in question may be present in the given species or it may be lacking, but present in the other group. In the first case a variety can only be formed by the loss of the character, in the second case it arises by the addition of a new one.

The first mode may be called a negative process, while the second is then to be designated as positive. And as it is more easy to lose what one has than to obtain something new, negative varieties are much more common than are positive ones.

Let us now take an instance of a character that is apt to vary in both ways, for this is obviously the best way of making clear what is meant by a negative and a positive change.

In the family of the composites we find a group of genera with two forms of florets on each flower-head. The hermaphrodite ones are tubular with 5, or rarely 4, equal teeth, and occupy the center of the head. These are often called the flosculous florets or disk-florets. Those of the circumference are ligulate and ordinarily unisexual, without stamens. In many cases they are sterile, having only an imperfect ovary. They are large and brightly colored and are generally designated as ray-florets. As instances we may cite the camomile (Anthemis nobilis), the wild camomile (Matricaria Chamomilla), [131] the yarrow (Achillea Millefolium), the daisies, the Dahlia and many others. Species occur in this group of plants from time to time that lack the ray-florets, as in the tansy (Tanacetum vulgare) and some artemisias. And the genus of the marigolds or Bidens is noted for containing both of these types. The smaller and the three-toothed marigold (B. cernua and B. tripartita) are very common plants of wet soil and swamps, ordinarily lacking the ray-florets, and in some countries they are very abundant and wholly constant in this respect, never forming radiate flower-heads. On the other hand the white-flowered and the purple marigold (B. leucantha and B. atropurpurea) are cultivated species of our gardens, prized for their showy flower-heads with large white or deeply colored, nearly black-purple florets.

Here we have opportunity to observe positive and negative varieties of the same character. The smaller, and the three-toothed marigold occur from time to time, provided with ray florets, showing a positive variation. And the white marigold has produced in our gardens a variety without rays. Such varieties are quite constant, never returning to the old species. Positive and negative varieties of this kind are by no means rare among the compositae.

[132] In systematic works the positive ones are as a rule called "radiate," and the negative ones "discoid." Discoid forms of the ordinary camomile, of the daisy, of some asters (Aster Tripolium), and of some centauries have been described. Radiate forms have been observed in the tansy (Tanacetum vulgare), the common horse-weed or Canada fleabane (Erigeron canadensis) and the common groundsel (Senecio vulgaris). Taken broadly the negative varieties seem to be somewhat more numerous than the positive ones, but it is very difficult to come to a definite conclusion on this point.

Quite the contrary is the case with regard to the color-varieties of red and blue flowers. Here the loss of color is so common that every one could give long lists of examples of it. Linnaeus himself supposed that no blue or red-colored wild species would be without a white variety. It is well known that he founded his often criticized prescript never to trust to color in recognizing or describing a species, on this belief.

On the other hand there are some red varieties of white-flowered species. But they are very rare, and little is known about their characters or constancy. Blue varieties of white species are not found. The yarrow (Achillea Millefolium) has a red-flowered form, which occurs [133] from time to time in sunny and sandy localities. I have isolated it and cultivated it during a series of years and during many generations. It is quite true to its character, but the degree of its coloring fluctuates between pink and white and is extremely variable. Perhaps it can be considered as an inconstant variety. A redflowered form of the common Begonia semperflorens is cultivated under the name of "Vernon," the white hawthorn (Crataegus Oxyacantha) is often seen with red flowers, and a pink-flowered variety of the "Silverchain" or "Bastard acacia" (Robinia Pseud-Acacia) is not rarely cultivated. The "Crown" variety of the yellow wall-flower and the black varieties, are also to be considered as positive color variations, the black being due in the latter cases to a very great amount of the red pigment.

Among fruits there are also some positive red varieties of greenish or yellowish species, as for instance the red gooseberry (Ribes Grossularia) and the red oranges. The red hue is far more common in leaves, as seen among herbs, in cultivated varieties of Coleus and in the brown leaved form of the ordinary white clover, among trees and shrubs in the hazelnut (Corylus), the beech (Fagus), the birch (Betula), the barberry (Berberis) and many others. But though most of these forms are very ornamental and abundant [134] in parks and gardens, little is as yet known concerning the origin of their varietal attributes and their constancy, when propagated by seeds. Besides the ray-florets and the colors, there are of course a great many other characters in which varieties may differ from their species. In most of the cases it is easy to discern whether the new character is a positive or a negative one. And it is not at all necessary to scrutinize very narrowly the list of forms to become convinced that the negative form is the one which prevails nearly everywhere, and that positive aberrations are in a general sense so rare that they might even be taken for exceptions to the rule.

Many organs and many qualities may be lost in the origination of a variety. In some instances the petals may disappear, as in Nigella, or the stamens, as in the Guelder-rose (Viburnum Opulus) and the Hortensia and in some bulbs even the whole flowers may be wanting, as in the beautiful "Plumosa" form of the cultivated grape-hyacinth or Muscari comosum. Fruits of the pineapples and bananas without seeds are on record as well as some varieties of apples and pears, of raisins and oranges. And some years ago Mr. Riviere of Algeria described a date growing in his garden that forms fruit without pits. The stoneless plum of Mr. [135] Burbank of Santa Rosa, California, is also a very curious variety, the kernel of which is fully developed but naked, no hard substance intervening between it and the pulp.

More curious still are the unbranched varieties consisting of a single stem, as may be seen sometimes in the corn or maize and in the fir. Fir-trees of some three or four meters in height without a single branch, wholly naked and bearing leaves only on the shoots of the last year's growth at the apex of the tree, may be seen. Of course they cannot bear seed, and so it is with the sterile maize, which never produces any seed-spikes or staminate flowers. Other seedless varieties can be propagated by buds; their origin is in most cases unknown, and we are not sure as to whether they should be classified with the constant or with the inconstant varieties.

A very curious loss is that of starch in the grains of the sugar-corn and the sugar-peas. It is replaced by sugar or some allied substance (dextrine). Equally remarkable is the loss of the runners in the so-called "Gaillon" strawberries.

Among trees the pendulous or weeping, and the broomlike or fastigiate forms are very marked varieties, which occur in species belonging to quite different orders. The ash, the beach, some willows, many other trees and some [136] finer species of garden-plants, as Sophora japonica, have given rise to weeping varieties, and the yew-tree or Taxus has a fastigiate form which is much valued because of its ascending branches and pyramidal habit. So it is with the pyramidal varieties of oaks, elms, the bastard-acacia and some others.

It is generally acknowledged that these forms are to be considered as varieties on the ground of their occurrence in so wide a range of species, and because they always bear the same attributes. The pendulous forms owe their peculiarity to a lengthening of the branches and a loss of their habit of growing upwards; they are too weak to retain a vertical position and the response to gravity, which is ordinarily the cause of the upright growth, is lacking in them. As far as we know, the cause of this weeping habit is the same in all instances. The fastigiate trees and shrubs are a counterpart of the weeping forms. Here the tendency to grow in a horizontal direction is lacking, and with it the bilateral and symmetric structure of the branches has disappeared. In the ordinary yew-tree the upright stem bears its needles equally distributed around its circumference, but on the branches the needles are inserted in two rows, one to the left and one to the right. All the needles turn their upper surfaces upwards, [137] and their lower surfaces downwards, and all of them are by this means placed in a single horizontal plane, and branching takes place in the same plane. Evidently this general arrangement is another response to gravity, and it is the failure of this reaction which induces the branches to grow upwards and to behave like stems.

Both weeping and fastigiate characters are therefore to be regarded as steps in a negative direction, and it is highly important that even such marked departures occur without transitions or intermediate forms. If these should occur, though ever so rarely, they would probably have been brought to notice, on account of the great prospect the numerous instances would offer. The fact that they are lacking, proves that the steps, though apparently great, are in reality to be considered as covering single units, that cannot be divided into smaller parts. Unfortunately we are still in the dark as to the question of the inheritance of these forms, since in most cases it is difficult to obtain pure seed.

We now consider the cases of the loss of superficial organs, of which the nectarines are example. These are smooth peaches, lacking the soft hairy down, that is a marked peculiarity of the true peaches. They occur in different [138] races of the peach. As early as the beginning of the past century, Gallesio described no less than eight subvarieties of nectarines, each related to a definite race of peach. Most of them reproduce themselves truly from seed, as is well known in this country concerning the clingstones, freestones and some other types. Nectarines have often varied, giving rise to new sorts, as in the case of the white nectarine and many others differing greatly in appearance and flavor. On the other hand it is to be remarked, that the trees do not differ in other respects and cannot be distinguished while young, the varietal mark being limited to the loss of the down on the fruit. Peaches have been known to produce nectarines, and nectarines to yield true peaches. Here we have another instance of positive and negative steps with reference to the same character, but I cannot withhold an expression of some doubt as to the possibility of crossing and subsequently splitting up of the hybrids as a more probable explanation of at least some of the cases quoted by various writers.

Smooth or glabrous varieties often occur, and some of them have already been cited as instances of the multiplication of varietal names. Positive aberrations are rather rare, and are mostly restricted to a greater density of the [139] pubescence in some hairy species, as in Galeopsis Ladanum canescens, Lotus corniculatus hirsutus and so on. But Veronica scutellata is smooth and has a pubescent variety, and Cytisus prostratus and C. spinescens are each recorded to have a ciliate form.

Comparable with the occurrence and the lack of hairs, is the existence or deficiency of the glaucous effect in leaves, as is well known in the common Ricinus. Here the glaucous appearance is due to wax distributed in fine particles over the surface of the leaves, and in the green variety this wax is lacking. Other instances could be given as in the green varieties of Papaver alpinum and Rumex scutatus. No positive instances are recorded in this case.

Spines and prickles may often disappear and give rise to unarmed and defenceless types. Of the thorn-apples both species, the whiteflowered Datura Stramonium and the purple D. Tatula have such varieties. Spinach has a variety called the "Dutch," which lacks the prickles of the fruit; it is a very old form and absolutely constant, as are also the thornless thorn-apples. Last year a very curious instance of a partial loss of prickles was discovered by Mr. Cockerell of East Las Vegas in New Mexico. It is a variety of the American cocklebur, often called sea-burdock, or the [140] hedgehog-burweed, a stout and common weed of the western states. Its Latin name is Xanthium canadense or X. commune and the form referred to is named by Mr. Cockerell, X. Wootoni, in honor of Professor E.o. Wooton who described the first collected specimens.