This discussion gives a very simple explanation of the acknowledged fact that the seeds of the extremes are in the main the best for the propagation of the race. It does not include however, all the causes for this preferment. Some are of older date and due to previous influences.

A second point in our discussion is the appreciation of the fact that a single individual may be chosen to gather the seed from, and that these seeds, and the young plants they yield, are as a rule, numerous. Hence it follows that we are to compare their average and their extremes with the qualities of the parents. Both are of practical as well as of theoretical interest. The average of the progeny is to be considered as the chief result of the selection in the previous generation, while the extremes, at least those which depart in the same direction, are obviously the means of further improvement of the race.

Thus our discussion should be divided into [773] two heads. One of these comprises the relation of the average of the progeny to the exceptional qualities of the chosen parent, and the other the relation of exceptional offspring to the exceptional parents.

Let us consider the averages first. Are they to be expected to be equal to the unique quality of the parent, or perhaps to be the same as the average of the whole unselected race? Neither of these cases occur. Experience is clear and definite on this important point. Vilmorin, when making the first selections to improve the amount of sugar in beets, was struck with the fact that the average of the progeny lies between that of the original strain and the quality of the chosen parent. He expressed his observation by stating that the progeny are grouped around and diverge in all directions from some point, placed on the line which unites their parent with the type from which it sprang. All breeders agree on this point, and in scientific experiments it has often been confirmed. We shall take up some illustrative examples presently, but in order to make them clear, it is necessary to give a closer consideration to the results of Vilmorin.

From his experience it follows that the average of the progeny is higher than that of the race at large, but lower than the chosen parent. [774] In other words, there is a progression and a regression. A progression in relation to the whole race, and a regression in comparison with the parent. The significance of this becomes clear at once, if we recall the constancy of the variety which could be obtained from the selected extreme in the case of vegetative multiplication. The progression is what the breeder wants, the regression what he detests. Regression is the permanency of part of the mediocrity which the selection was invoked to overcome. Manifestly it is of the highest interest that the progression should be as large, and the regression as small as possible. In order to attain this goal the first question is to know the exact measure of progression and regression as they are exhibiting themselves in the given cases, and the second is to inquire into the influences, on which this proportion may be incumbent.

At present our notions concerning the first point are still very limited and those concerning the second extremely vague. Statistical inquiries have led to some definite ideas about the importance of regression, and these furnish a basis for experimental researches concerning the causes of the phenomenon. Very advantageous material for the study of progression and regression in the realm of fluctuating variability is afforded by the [775] ears of corn or maize. The kernels are arranged in longitudinal rows, and these rows are observed to occur in varying, but always even, numbers. This latter circumstance is due to the fact that each two neighboring rows contain the lateral branches of a single row of spikelets, the ages of which however, are included in the fleshy body of the ear. The variation of the number of the rows is easily seen to comply with Quetelet's law, and often 30 or 40 ears suffice to give a trustworthy curve. Fritz Muller made some experiments upon the inheritance of the number of the rows, in Brazil. He chose a race which averaged 12 rows, selected ears with 14, 16 and 18 rows, etc., and sowed their kernels separately. In each of-these cultures he counted the rows of the seeds on the ears of all the plants when ripe, and calculated their average. This average, of course, does not necessarily correspond to a whole number, and fractions should not be neglected.

According to Vilmorin's rule he always found some progression of the average and some regression. Both were the larger, the more the parent-ear differed from the general average, but the proportion between both remained the same, and seems independent of the amount of the deviation. Putting the deviation at 5, the progression calculated from his figures is [776] 2 and the regression 3. In other words the average of the progeny has gained over the average of the original variety slightly more than one-third, and slightly less than one-half of the parental deviation. I have repeated this experiment of Fritz Miller's and obtained nearly the same regression of three-fifths, though working with another variety, and under widely different climatic conditions.

The figures of Fritz Muller were, as given below, in one experiment. In the last column I put the improvement calculated for a proportion of two-fifths above the initial average of 12.

Rows on Average of rows 12 + 2/5 of parent ears of progeny Difference 14 12.6 12.8 16 14.1 13.6 18 15.2 14.4 20 15.8 15.2 22 16.1 16.0

Galton, in his work on natural inheritance, describes an experiment with the seeds of the sweet pea or Lathyrus odoratus. He determined the average size in a lot of purchased seeds, and selected groups of seeds of different, but for each group constant, sizes. These were sown, and the average of the seeds was determined anew in the subsequent harvest they yielded. These figures agreed with the rule of Vilmorin and were calculated in the manner [777] given for the test of the corn. The progression and regression were found to be proportionate to the amount of the deviation. The progression of the average was one-third, and the regression in consequence two-thirds of the total deviation. The amelioration is thus seen to be nearly, though not exactly, the same as in the previous case.

From the evidence of the other corresponding experiments, and from various statistical inquiries it seems that the value of the progression is nearly the same in most cases, irrespective of the species used and the quality considered. It may be said to be from one-third to one-half of the parental deviation, and in this form the statement is obviously of wide and easy applicability.

Our figures also demonstrate the great preeminence of vegetative varieties above the improved strains multiplied by seeds. They have a definite relation. Asexually multiplied strains may be said to be generally two times or even three times superior to the common offspring. This is a difference of great practical importance, and should never be lost sight of in theoretical considerations of the productive capacity of selection. Multiplication by seed however, has one great advantage over the asexual method; it may be repeated. The [778] selection is not limited to a single choice, but may be applied in two or more succeeding generations. Obviously such a repetition affords a better chance of increasing the progression of the average and of ameliorating the race to a greater degree than would be possible by a single choice. This principle of repeated selection is at present the prominent feature of race improvement. Next to variety-testing and hybridizing it is the great source of the steady progression of agricultural crops. From a practical standpoint the method is clear and as perfect as might be expected, but this is not the side of the problem with which we are concerned here. The theoretical analysis and explanation of the results obtained, however, is subject to much doubt, and to a great divergence of conceptions. So it is also with the application of the practical processes to those occurring in nature. Some assume that here repeated selection is only of subordinate importance, while others declare that the whole process of evolution is due to this agency. This very important point however, will be reserved for the next lecture, and only the facts available at present will be considered here.

As a first example we may take the ray-florets of the composites. On a former occasion we have dealt with their fluctuation in number and [779] found that it is highly variable and complies in the main with Quetelet's law. Madia elegans, a garden species, has on the average 21 rays on each head, fluctuating between 16 and 25 or more. I saved the seeds of a plant with only 17 rays on the terminal head, and got from them a culture which averaged 19 rays, which is the mean between 21 and 17. In this second generation I observed the extremes to be 22 and 12, and selected a plant with 13 rays as the parent for a continuation of the experiment. The plants, which I got from its seeds, averaged 18 and showed 22 and 13 as extremes. The total progression of the average was thus, in two generations, from 21 to 18, and the total regression from 13 to 18, and the proportion is thus seen to diminish by the repetition rather than to increase.

This experiment, however, is of course too imperfect upon which to found general conclusions. It only proves the important fact that the improved average of the second generation is not the starting-point for the further improvement. But the second generation allows a choice of an extreme, which diverges noticeably more from the mean than any individual of the first culture, and thereby gives a larger amount of absolute progression, even if the proportion between progression and regression remains [780] the same. The repetition is only an easy method of getting more widely deviating extremes; whether it has, besides this, another effect, remains doubtful. In order to be able to decide this question, it is necessary to repeat the selection during a series of generations. In this way the individual faults may be removed as far as possible. I chose an experiment of Fritz Muller, relating to the number of rows of grains on the ears exactly as in the case above referred to, and which I have repeated in my experimental garden at Amsterdam.

I started from a variety known to fructify fairly regularly in our climate, and exhibiting in the mean 12-14 rows, but varying between 8 and 20 as exceptional cases. I chose an ear with 16 rows and sowed its seeds in 1887. A number of plants were obtained, from each of which, one ear was chosen in order to count its rows. An average of 15 rows was found with variations complying with Quetelet's law. One ear reached 22 rows, but had not been fertilized, some others had 20 rows, and the best of these was chosen for the continuation of the experiment. I repeated the sowing during 6 subsequent generations in the same way, choosing each time the most beautiful ear from among those with the greatest number of rows. Unfortunately with the increase of the number the [781] size of the grains decreases, the total amount of nourishment available for all of them remaining about the same. Thus the kernels and consequently the new plants became smaller and weaker, and the chance of fertilization was diminished in the ears with the highest number of rows. Consequently the choice was limited, and after having twice chosen a spike with 20 and once one with 24 rows, I finally preferred those with the intermediate number of 22.

This repeated choice has brought the average of my race up from 13 to 20, and thus to the extreme limit of the original variety. Seven years were required to attain this result, or on an average the progression was one row in a year. This augmentation was accompanied by an accompanying movement of the whole group in the same direction. The extreme on the side of the small numbers came up from 8 to 12 rows, and cobs with 8 or 10 rows did not appear in my race later than the third generation. On the other side the extreme reached 28, a figure never reached by the original variety as cultivated with us, and ears with 24 and 26 rows have been seen during the four last generations in increasing numbers.

This slow and gradual amelioration was partly due to the mode of pollination of the corn. [782] The pollen falls from the male spikes on the ears of the same plant, but also is easily blown on surrounding spikes. In order to get the required amount of seed it is necessary in our climate to encroach as little as possible upon free pollination, aiding the self-pollination, but taking no precautions against intercrossing. It is assumed that the choice of the best ears indicates the plants which have had the best pollen-parents as well as the best pistil parents, and that selection here, as in other cases, corrects the faults of free intercrossing. But it is granted that this correction is only a slow one, and accounts in a great degree for the slowness of the progression. Under better climatic conditions and with a more entire isolation of the individuals, it seems very probable that the same result could have been reached in fewer generations.

However this may be, the fact is that by repeated selection the strain can be ameliorated to a greater extent than by a single choice. This result completely agrees with the general experience of breeders and the example given is only an instance of a universal rule. It has the advantage of being capable of being recorded in a numerical way, and of allowing a detailed and definite description of all the succeeding generations. The entire harvest of all [783] of them has been counted and the figures combined into curves, which at once show the whole course of the pedigree-experiment. These curves have in the main taken the same shape, and have only gradually been moved in the chosen direction.

Three points are now to be considered in connection with this experiment. The first is the size of the cultures required for the resulting amelioration. In other words, would it have been possible to attain an average of 20 rows in a single experiment? This is a matter of calculation, and the calculation must be based upon the experience related above, that the progression in the case of maize is equal to two-fifths of the parental deviation. A cob with 20 rows means a deviation of 7 from the average of 13, the incipient value of my race. To reach such an average at once, an ear would be required with 7 x 5/2 = 17-1/2 rows above the average, or an ear with 30-32 rows. These never occur, but the rule given in a previous lecture gives a method of calculating the probability of their occurrence, or in other words, the number of ears required to give a chance of finding such an ear. It would take too long to give this calculation here, but I find that approximately 12,000 ears would be required to give one with 28 rows, which was the highest number attained in [784] my experiment, while 100,000 ears would afford a chance of one with 32 rows*. Had I been able to secure and inspect this number of ears, perhaps I would have needed only a year to get an average of 20 rows. This however, not being the case, I have worked for seven years, but on the other hand have cultivated all in all only about one thousand individuals for the entire experiment.

Obviously this reduction of the size of the experiment is of importance. One hundred thousand ears of corn could of course, be secured directly from trade or from some industrial culture, but corn is cultivated only to a small extent in Holland, and in most cases the requisite number of individuals would be larger than that afforded by any single plantation.

Repeated selection is thereby seen to be the means of reducing the size of the required cultures to possible measures, not only in the experimental-garden, but also for industrial purposes. A selection from among 60,000-100,000 individuals may be within reach of Burbank, but of few others. As a rule they prefer a longer time with a smaller lot of plants. This

* On about 200 ears the variability ranges from 8-22 rows, and this leads approximately to one row more by each doubling of the numbers of instances. One ear with 22 rows in 200 would thus lead to the expectation of one ear with 32 rows in 100,000 ears.

[785] is exactly what is gained by repeated selections. To my mind this reduction of the size of the cultures is probably the sole effect of the repetition. But experience is lacking on this point, and exact comparisons should be made whenever possible, between the descendants of a unique but extreme choice, and a repeated but smaller selection. The effect of the repetition on the nourishment of the chosen representatives should be studied, for it is clear that a plant with 22 rows, the parents and grandparents of which had the same number, indicates a better condition of internal qualities than one with the same number of rows, produced accidentally from the common race. In this way it may perhaps be possible to explain, why in my experiment an ear with 22 rows gave an average offspring with 20, while the calculation, founded on the regression alone would require a parental ear with 32 rows.

However, as already stated, this discussion is only intended to convey some general idea as to the reduction of the cultures by means of repeated selections, as the material at hand is wholly inadequate for any closer calculation. This important point of the reduction may be illustrated in still another manner.

The sowing of very large numbers is only required because it is impossible to tell from the [786] inspection of the seeds which of them will yield the desired individual. But what is impossible in the inspection of the seeds may be feasible, at least in important measure, in the inspection of the plants which bear the seeds. Whenever such an inspection demonstrates differences, in manifest connection with the quality under consideration, any one will readily grant that it would be useless to sow the seeds of the worst plants, and that even the whole average might be thrown over, if it were only possible to point out a number of the best. But it is clear that by this inspection of the parent plants the principle of repeated selection is introduced for two succeeding generations, and that its application to a larger series of generations is only a question of secondary importance.

Summing up our discussion of this first point we may assert that repeated selection is only selection on a small and practical scale, while a single choice would require numbers of individuals higher than are ordinarily available.

A second discussion in connection with our pedigree-culture of corn is the question whether the amelioration obtained was of a durable nature, or only temporary. In other words, whether the progeny of the race would remain constant, if cultivated after cessation of the selection. In order to ascertain this, [787] I continued the culture during several generations, choosing ears with less than the average number of rows. The excellence of the race at once disappeared, and the ordinary average of the variety from which I had started seven years before, returned within two or three seasons. This shows that the attained improvement is neither fixed nor assured and is dependent on continued selection. This result only confirms the universal experience of breeders, which teaches the general dependency of improved races on continued selection. Here a striking contrast with elementary species or true varieties is obvious. The strains which nature affords are true to their type; their average condition remains the same during all the succeeding generations, and even if it should be slightly altered by changes in the external conditions, it returns to the type, as soon as these changes come to an end. It is a real average, being the sum of the contribution of all the members of the strain. Improved races have only an apparent average, which is in fact biased by the exclusion of whole groups of individuals. If left to themselves, their appearance changes, and the real average soon returns. This is the common experience of breeders.

A third point is to be discussed in connection [788] with the detailed pedigree-cultures. It is the question as to what might be expected from a continuation of improvement selection. Would it be possible to obtain any imaginable deviation from the original type, and to reach independency from further selection? This point has not until now attracted any practical interest, and from a practical point of view and within the limits of ordinary cultures, it seems impossible to obtain a positive answer. But in the theoretical discussion of the problems of descent it has become of the highest importance, and therefore requires a separate treatment, which will be reserved for the next lecture.

Here we come upon another equally difficult problem. It relates to the proportion of embryonic or individual fluctuation, to partial variation as involved in the process of selection. Probably all qualities which may be subjected to selection vary according to both principles, the embryonic decision giving only a more definite average, around which the parts of the individual are still allowed to oscillate. It is so with the corn, and whenever two or more ears are ripening or even only flowering on the same plant, differences of a partial nature may be seen in the number of their rows. These fluctuations are only small however, ordinarily not exceeding two and rarely four [789] rows. Choosing always the principal ear, the figures may be taken to indicate the degree of personal deviation from the average of the race. But whenever we make a mistake, and perchance sow from an ear, the deviation of which was largely due to partial variation, the regression should be expected to become considerably larger. Hence it must be conceded that exact calculations of the phenomena of inheritance are subject to much uncertainty, resulting from our very imperfect knowledge concerning the real proportion of the contributing factors, and the difficulty of ascertaining their influence in any given case. Here also we encounter more doubts than real facts, and much remains to be done before exact calculations may become of real scientific value.

Returning to the question of the effects of selection in the long run, two essentially different cases are to be considered. Extremes may be selected from among the variants of ordinary fluctuating variability, or from ever-sporting varieties. These last we have shown to be double races. Their peculiar and wide range of variability is due to the substitution of two characters, which exclude one another, or if combined, are diminished in various degrees. Striped flowers and stocks, "five-leaved" clover, pistilloid opium-poppies and numerous other [790] monstrosities have been dealt with as instances of such ever-sporting varieties.

Now the question may be put, what would be the effect of selection if in long series of years one of the two characters of such a double race were preferred continuously, to the complete exclusion of the other. Would the race become changed thereby? Could it be affected to such a degree as to gradually lose the inactive quality, and cease to be a double race?

Here manifestly we have a means by which to determine what selection is able to accomplish. Physiologic experiments may be said to be too short to give any definite evidence. But cases may be cited where nature has selected during long centuries and with absolute constancy in her choice. Moreover unconscious selections by man have often worked in an analogous manner, and many cultivated plants may be put to the test concerning the evidence they might give on this point. Stating beforehand the result of this inquiry, we may assert that long-continued selection has absolutely no appreciable effect. Of course I do not deny the splendid results of selection during the first few years, nor the necessity of continued selection to keep the improved races to the height of their ameliorated qualities. I only wish to state that the work [791] of selection here finds its limit and that centuries and perhaps geologic periods of continued effort in the same direction are not capable of adding anything more to the initial effect. Some illustrative examples may suffice to prove the validity of this assertion. Every botanist who has studied the agricultural practice of plant-breeding, or the causes of the geographic distribution of plants, will easily recall to his mind numerous similar cases. Perhaps the most striking instance is afforded by cultivated biennial plants. The most important of them are forage-beets and sugar-beets. They are, of course, cultivated only as biennials, but some annual specimens may be seen each year and in nearly every field. They arise from the same seed as the normal individuals, and their number is obviously dependent on external conditions, and especially on the time of sowing. Ordinary cultures often show as much as 1% of these useless plants, but the exigencies of time and available labor often compel the cultivator to have a large part of his fields sown before spring. In central Europe, where the climate is unfavorable at this season, the beets respond by the production of far larger proportions of annual specimens, their number coming often up to 20% or more, thus constituting noticeable losses in the product [792] of the whole field. Rimpau, who has made a thorough study of this evil and has shown its dependency on various external conditions, has also tried to find methods of selection with the aim of overcoming it, or at least of reducing it to uninjurious proportions. But in these efforts he has reached no practical result. The annuals are simply inexterminable.

Coming to the alternative side of the problem it is clear that annuals have always been excluded in the selection. Their seeds cannot be mixed with the good harvest, not even accidentally, since they have ripened in a previous year. In order to bear seeds in the second year beets must be taken from the field, and kept free from frost through the winter. The following spring they are planted out, and it is obvious that even the most careless farmer is not liable to mix them with annual specimens. Hence we may conclude that a strict and unexcelled process of selection has been applied to the destruction of this tendency, not only for sugar-beets, since Vilmorin's time, when selection had become a well understood process, but also for forage-beets since the beginning of beet culture. Although unconscious, the selection of biennials must have been uninterrupted and strict throughout many centuries.

It has had no effect at all. Annuals are seen [793] to return every year. They are ineradicable. Every individual is in the possession of this latent quality and liable to convert it into activity as soon as the circumstances provoke its appearance, as proved by the increase of annuals in the early sowings. Hence the conclusion that selection in the long run is not adequate to deliver plants from injurious qualities. Other proofs could be given by other biennials, and among them the stray annual plants of common carrots are perhaps the most notorious. In my own cultures of evening-primroses I have preferred the annuals and excluded the biennials, but without being able to produce a pure annual race. As soon as circumstances are favorable, the biennials return in large numbers. Cereals give analogous proofs. Summer and winter varieties have been cultivated separately for centuries, but in trials it is often easy to convert the one into the other. No real and definite isolation has resulted from the effect of the long continued unconscious selection.

Striped flowers, striped fruits, and especially striped radishes afford further examples. It would be quite superfluous to dwell upon them. Selection always tends to exclude the monochromatic specimens, but does not prevent their return in every generation. Numerous [794] rare monstrosities are in the same category, especially when they are of so rare occurrence as not to give any noticeable contribution to the seed-production, or even if they render their bearers incapable of reproduction. In such cases the selection of normal plants is very severe or even absolute, but the anomalies are by no means exterminated. Any favorable circumstances, or experimental selection in their behalf shows them to be still capable of full development. Numerous cases of such subordinate hereditary characters constitute the greater part of the science of vegetable teratology.

If it should be objected that all these cases cover too short a time to be decisive, or at least fail in giving evidence relative to former times, alpine plants afford a proof which one can hardly expect to be surpassed. During the whole present geologic epoch they have been subjected to the never failing selection of their climate and other external conditions. They exhibit a full and striking adaptation to these conditions, but also possess the latent capacity for assuming lowland characters as soon as they are transported into such environment. Obviously this capacity never becomes active on the mountains, and is always counteracted by selection. This agency is evidently without any effect, for as we have seen when dealing [795] with the experiments of Nageli, Bonnier and others, each single individual may change its habits and its aspect in response to transplantation. The climate has an exceedingly great influence on each individual, but the continuance of this influence is without permanent result.

So much concerning ever-sporting varieties and double adaptations. We now come to the effects of a continuous selection of simple characters.

Here the sugar-beets stand preeminent. Since Vilmorin's time they have been selected according to the amount of sugar in their roots, and the result has been the most striking that has ever been attained, if considered from the standpoint of practice. But if critically examined, with no other aim than a scientific appreciation of the improvement in comparison with other processes of selection, the support of the evidence for the theory of accumulative influence proves to be very small.

The amount of sugar is expressed by percentage-figures. These however, are dependent on various causes, besides the real quantity of sugar produced. One of these causes is the quantity of watery fluid in the tissues, and this in its turn is dependent on the culture in dryer or moister soil, and on the amount of moisture in the air, and the same variety of sugar-beets [796] yields higher percentage-figures in a dry region than in a wet one. This is seen when comparing, for instance, the results of the analyses from the sandy provinces of Holland with those from the clay-meadows, and it is very well known that Californian beets average as high as 26% or more, while the best European beets remain at about 20%. As far as I have been able to ascertain, these figures however, are not indicative of any difference of race, but simply direct responses to the conditions of climate and of soil.

Apart from these considerations the improvement reached in half a century or in about twenty to thirty generations is not suggestive of anything absolute. Everything is fluctuating now, even as it was at the outset, and equally dependent on continual care. Vilmorin has given some figures for the beets of the first generations from which he started his race. He quotes 14% as a recommendable amount, and 7 and 21 as the extreme instances of his analyses. However incorrect these figures may be, they coincide to a striking degree with the present condition of the best European races. Of course minor values are excluded each year by the selection, and in consequence the average value has increased. For the year 1874 we find a standard of 10-14% considered as normal, [797] bad years giving 10%, good years from 12% to 14% in the average. Extreme instances exceeded 17%. From that time the practice of the polarization of the juice for the estimate of the sugar has rapidly spread throughout Europe, and a definite increase of the average value soon resulted. This however, often does not exceed 14%, and beets selected in the field for the purpose of polarization come up to an average of 15 to 16%, varying downward to less than 10% and upward to 20 and 21%. In the main the figures are the same as those of Vilmorin, the range of variability has not been reduced, and higher extremes are not reached. An average increase of 1% is of great practical importance, and nothing can excel the industry and care displayed in the improvement of the beet-races. Notwithstanding this a lasting influence has not been exercised; the methods of selection have been improved, and the number of polarized beets has been brought up to some hundreds of thousands in single factories, but the improvement is still as dependent upon continuous selection as it was half a century ago.

The process is practically very successful, but the support afforded by it to the selection theory vanishes on critical examination.

[798]

LECTURE XXVIII

ARTIFICIAL AND NATURAL SELECTION

The comparison of artificial and natural selection has furnished material support for the theory of descent, and in turn been the object of constant criticism since the time of Darwin. The criticisms, in greater part, have arisen chiefly from an imperfect knowledge of both processes. By the aid of distinctions recently made possible, the contrast between elementary species and improved races has become much more vivid, and promises to yield better results on which to base comparisons of artificial and natural selection.

Elementary species, as we have seen in earlier lectures, occur in wild and in cultivated plants. In older genera and systematic species they are often present in small numbers only, but many of the more recent wild types and also many of the cultivated forms are very rich in this respect. In agriculture the choice of the most adequate elementary forms for any special purpose is acknowledged [799] as the first step in the way of selection, and is designated by the name of variety-testing, applying the term variety to all the subdivisions of systematic species indiscriminately. In natural processes it bears the title of survival of species. The fact that recent types show large numbers, and in some instances even hundreds of minor constant forms, while the older genera are considerably reduced in this respect, is commonly explained by the assumption of extinction of species on a correspondingly large scale. This extinction is considered to affect the unfit in a higher measure than the fit. Consequently the former vanish, often without leaving any trace of their existence, and only those that prove to be sufficiently adapted to the surrounding external conditions, resist and survive.

This selection exhibits far-reaching analogies between the artificial and the natural processes, and is in both cases of the very highest importance. In nature the dying out of unfit mutations is the result of the great struggle for life. In a previous lecture we have compared its agency with that of a sieve. All elements which are too small or too weak fall through, and only those are preserved which resist the sifting process. Reduced in number they thrive and multiply and are thus enabled to [800] strike out new mutative changes. These are again submitted to the sifting tests, and the frequent repetition of this process is considered to give a good explanation of the manifold, highly complicated, and admirable structures which strike the beginner as the only real adaptations in nature.

Exactly in the same way artificial selection isolates and preserves some elementary species, while it destroys others. Of course the time is not sufficient to secure new mutations, or at least these are only rare at present, and their occurrence is doubtful in historic periods. Apart from this unavoidable difference the analogy between natural and artificial selection appears to me to be very striking.

This form of selection may be termed selection between species. Opposed to it stands the selection within the elementary species or variety. It has of late, alone come to be known as selection, though in reality it does not deserve this distinction. I have already detailed the historical evidence which gives preference to selection between species. The process can best be designated by the name of intraspecific selection, if it is understood that the term intraspecific is meant to apply to the conception of small or elementary species.

I do not wish to propose new terms, but [801] I think that the principal differences might better become understood by the introduction of the word election into the discussion of questions of heredity. Election meant formerly the preferential choice of single individuals, while the derivation of the word selection points to a segregation of assemblies into their larger parts. Or to state it in a shorter way, individual selection is exactly what is usually termed election. Choosing one man from among thousands is to elect him, but a select party is a group of chosen persons. There would be no great difficulty in the introduction of the word election, as breeders are already in the habit of calling their choice individuals "elite," at least in the case of beets and of cereals.

This intraspecific selection affords a second point for the comparison between natural and artificial processes. This case is readily granted to be more difficult than the first, but there can be no doubt that the similarity is due to strictly comparable causes. In practice this process is scarcely second in importance to the selection between species, and in numerous cases it rests upon it, and crowns it, bringing the isolated forms up to their highest possible degree of usefulness. In nature it does quite the same, adapting strains of individuals to the local conditions of their environment. Improved [802] races do not generally last very long in practice; sooner or later they are surpassed by new selections. Exactly so we may imagine the agency of natural intraspecific selection. It produces the local races, the marks of which disappear as soon as the special external conditions cease to act. It is responsible only for the smallest lateral branches of the pedigree, but has nothing in common with the evolution on the main stems. It is of very subordinate importance.

These assertions of course, are directly opposed to the current run of scientific belief, but they are supported by facts. A considerable part of the evidence has already been dealt with and for our closing discussion only an exact comparison remains to be made between the two detailed types of intraspecific selection. In coming to this I will first dwell upon some intermediate types and conclude with a critical discussion of the features of artificial selection, which to my mind prove the invalidity of the conclusions drawn from it in behalf of an explanation of the processes of nature.

Natural selection occurs not only in the wild state, but is also active in cultivated fields. Here it regulates the struggle of the selected varieties and improved races with the older types, and even with the wild species. In a previous [803] lecture I have detailed the rapid increase of the wild oats in certain years, and described the experiments of Risler and Rimpau in the running out of select varieties. The agency is always the same. The preferred forms, which give a larger harvest, are generally more sensitive to injurious influences, more dependent on rich manure and on adequate treatment. The native varieties have therefore the advantage, when climatic or cultural conditions are unfavorable for the fields at large. They suffer in a minor degree, and are thereby enabled to propagate themselves afterwards more rapidly and to defeat the finer types. This struggle for life is a constant one, and can easily be followed, whenever the composition of a strain is noted in successive years. It is well appreciated by breeders and farmers, because it is always liable to counteract their endeavors and to claim their utmost efforts to keep their races pure. There can be no doubt that exactly the same struggle exempt from man's intrusion is fought out in the wild state.

Local races of wild plants have not been the object for field observations recently. Some facts however, are known concerning them. On the East Friesian Islands in the North Sea the flowers are strikingly larger and brighter colored than those of the same species on the [804] neighboring continent. This local difference is ascribed by Behrens to a more severe selection by the pollinating insects in consequence of their lesser frequency on these very windy isles. Seeds of the pines from the Himalayas yield cold-resisting young plants if gathered from trees in a high altitude, while the seeds of the same species from lower regions yield more sensitive seedlings. Similar instances are afforded by Rhododendron and other mountain species. According to Cieslar corresponding differences are shown by seeds of firs and larches from alpine and lowland provinces.

Such changes are directly dependent on external influences. This is especially manifest in experiments extending the cultures in higher or in more northern regions. The shorter summer is a natural agent of selection; it excludes all individuals which cannot ripen their seeds during so short a period. Only the short lived ones survive. Schubeler made very striking experiments with corn and other different cereals, and has succeeded in making their culture possible in regions of Norway where it formerly failed. In the district of Christiania, corn had within some few years reduced its lifetime from 123 to 90 days, yielding smaller stems and fewer kernels, but still sufficient to make its culture profitable under the existing conditions. [805] This change was not permanent, but was observed to diminish rapidly and to disappear entirely, whenever the Norwegian strain was cultivated in the southern part of Germany. It was a typical improved race, dependent on continual selection by the short summers which had produced it. Similar results have been reached by Von Wettstein in the comparison of kinds of flax from different countries. The analogy between such cultivated local races and the local races of nature is quite striking. The practice of seed exchange rests for a large part on the experience that the characters, acquired under the definite climatic and cultural conditions of some select regions, hold good for one or two, and sometimes even more generations, before they decrease to practical uselessness. The Probstei, the Hanna and other districts owe their wealth to this temporary superiority of their wheat and other cereals.

Leaving these intermediate forms of selection, we now come to our principal point. It has already been discussed at some length in the previous lecture, but needs further consideration. It is the question whether intraspecific selection may be regarded as a cause of lasting and ever-increasing improvement. This is assumed by biologists who consider fluctuating variability as the main source of progression [806] in the organic world. But the experience of the breeders does not support this view, since the results of practice prove that selection according to a constant standard soon reaches a limit which it is not capable of transgressing. In order to attain further improvements the method of selection itself must be improved. A better and sharper method assures the choice of more valuable representatives of the race, even if these must be sought for in far larger numbers of individuals, as is indicated by the law of Quetelet.

Continuous or even prolonged improvement of a cultivated race is not the result of frequently repeated selection, but of the improvement of the standard of appreciation. Nature, as far as we know, changes her standard from time to time only in consequence of the migrations of the species, or of local changes of climate. Afterwards the new standard remains unchanged for centuries.

Selection, according to a constant standard, reaches its results in few generations. The experience of Van Mons and other breeders of apples shows that the limit of size and lusciousness may be soon attained. Vilmorin's experiments with wild carrots and those of Carriere with radishes lead to the same conclusion as regards roots. Improvements of flowers in [807] size and color are usually easy and rapid in the beginning, but an impassable limit is soon reached. Numerous other instances could be given.

Contrasted with these simple cases is the method of selecting sugar beets. More than once I have alluded to this splendid example of the influence of man upon domestic races, and tried to point out how little support it affords to the current scientific opinion concerning the power of natural selection. For this reason it is interesting to see how a gradual development of the methods of selection has been, from the very outset, one of the chief aims of the breeders. None of them doubts that an improvement of the method alone is adequate to obtain results. This result, in the main, is the securing of a few percent more of sugar, a change hardly comparable with that progress in evolution, which our theories are destined to explain.

Vilmorin's original method was a very simple one. Polarization was still undiscovered in his time. He determined the specific weight of his beets, either by weighing them as a whole, or by using a piece cut from the base of the roots and deprived of its bark, in order to test only the sugar tissues. The pieces were floated in solutions of salt, which were diluted until the pieces [808] began to sink. Their specific weight at that moment was determined and considered to be a measure of the corresponding value of the beet. This principle was afterwards improved in two ways. The first was a selection after the salt solution method, but performed on a large scale. After some few determinations, a solution was made of such strength as to allow the greater number of the beets to float, and only the best to sink down. In large vessels thousands of beets could be tested in this way, to select a few of the very heaviest. The other improvement was the determination of the specific weight of the sap, pressed out from the tissue. It was more tedious and more expensive, but more direct, as the influence of the air cavities of the tissue was excluded. It prepared the way for polarization.

This was introduced about the year 1874 in Germany, and soon became generally accepted. It allowed the amount of sugar to be measured directly, and with but slight trouble. Thousands of beets could be tested yearly by this method, and the best selected for the production of seed. In some factories a standard percentage is determined by previous inquiries, and the mass of the beets is tested only by it. In others the methods of taking samples and clearing the sap have been improved so far as to allow the [809] exact determination of three hundred thousand polarization values of beets within a few weeks. Such figures give the richest material for statistical studies, and at once indicate the best roots, while they enable the breeder to change his standard in accordance with the results at any time. Furthermore they allow the mass of the beets to be divided into groups of different quality, and to produce, besides the seeds for the continuation of the race, a first class and second-class product and so on. In the factory of Messrs. Kuhn & Co., at Naarden, Holland, the grinding machine has been markedly improved, so as to tear all cell walls asunder, open all cells, and secure the whole of the sap within less than a minute, and without heating.

It would take too long to go into further details, or to describe the simultaneous changes that have been applied to the culture of the elite strains. The detailed features suffice to show that the chief care of the breeder in this case is a continuous amelioration of the method of selecting. It is manifest that the progression of the race is in the main due to great technical improvements, and not solely to the repetition of the selection.

Similar facts may be seen on all the great lines of industrial selection. An increasing appreciation [810] of all the qualities of the selected plants is the common feature. Morphological characters, and the capacity of yielding the desired products, are the first points that strike the breeder. The relation to climate and the dependence on manure soon follow; but the physiological and chemical sides of the problem are usually slow of recognition in the methods of selection. When visiting Mr. de Vilmorin at Paris some years ago, I inspected his laboratory for the selection of potatoes. In the method in use, the tubers were rubbed to pulp and the starch was extracted and measured. A starch percentage figure was determined for each plant, and the selection of the tubers for planting was founded upon this result. In the same way wheat has been selected by Dippe at Quedlinburg, first by a determination of its nitrogenous contents in general, and secondly by the amount of the substances which determine its value for baking purposes.

The celebrated rye of Schlanstedt was produced by the late Mr. Rimpau in a similar manner and was put on the market between 1880 and 1890 and was received with great favor throughout central Europe, especially in Germany and in France. It is a tall variety, with vigorous stems and very long heads, the kernels of which are nearly double the size of those of the [811] ordinary rye, and are seen protruding, when ripe, from between the scales of the spikelets. It is unfit for poor soils, but is one of the very best varieties for soils of medium fertility in a temperate climate. It is equal in the production of grain to the best French sorts, but far surpassing them in its amount of straw. It was perfected at the farm of Schlanstedt very slowly, according to the current conceptions of the period. The experiment was started in the year 1866, at which time Rimpau collected the most beautiful heads from among his fields, and sowed their kernels in his experiment garden. From this first culture the whole race was derived. Every year the best ears of the strain were chosen for repeated culture, under experimental care, while the remainder was multiplied in a field to furnish the seeds for large and continually increasing areas of his farms.

Two or three years were required to produce the quantity of seed of each kind required for all the fields of Schlanstedt. The experiment garden, which through the kindness of Mr. Rimpau I had the good fortune of visiting more than once between 1875 and 1878, was situated in the middle of his farm, at some distance from the dwellings. Of course it was treated with more care, and especially kept [812] in better conditions of fertility than was possible for the fields at large. A continued study of the qualities and exigencies of the elite plants accompanied this selection, and gave the means of gradually increasing the standard. Resistance against disease was observed and other qualities were ameliorated in the same manner. Mr. Rimpau repeatedly told me that he was most anxious not to overlook any single character, because he feared that if any of them might become selected in the wrong way, perchance unconsciously, the whole strain might suffer to such a degree as to make all the other ameliorations quite useless. With this purpose the number of plants per acre was kept nearly the same as those in the fields, and the size of the culture was large enough every year to include the best kernels of quite a number of heads. These were never separated, and exact individual pedigrees were not included in the plan. This mixture seemed to have the advantage of keeping up an average value of the larger number of the characters, which either from their nature or from their apparent unimportance had necessarily to be neglected.

After ten years of continuous labor, the rye of Rimpau caught the attention of his neighbors, being manifestly better than that of ordinary [813] sowings. Originally he had made his cultures for the improvement of his own fields only. Gradually however, he began to sell his product as seed to others, though he found the difference still very slight. After ten years more, about 1886, he was able to sell all his rye as seed, thereby making of course large profits. It is now acknowledged as one of the best sorts, though in his last letter Mr. Rimpau announced to me that the profits began to decline as other selected varieties of rye became known. The limit of productiveness was reached, and to surmount this, selection had to be begun again from some new and better starting point.

This new starting point invokes quite another principle of selection, a principle which threatens to make the contrast between artificial and natural selection still greater. In fact it is nothing new, being in use formerly in the selection of domestic animals, and having been applied by Vilmorin to his sugar beets more than half a century ago. Why it should ever have been overlooked and neglected in the selection of sugar beets now is not clear.

The principle in itself is very simple. It agrees that the visible characters of an animal or a plant are only an imperfect measure for its hereditary qualities, instead of being the real criterion to be relied upon, as is the current belief. [814] It further reasons that a direct appreciation of the capacity of inheritance can only be derived from the observation of the inheritance itself. Hence it concludes that the average value of the offspring is the only real standard by which to judge the representatives of a race and to found selection upon.

These statements are so directly opposed to views prevalent among plant breeders, that it seems necessary to deal with them from the theoretical and experimental, as well as from the practical side.

The theoretical arguments rest on the division of the fluctuating variability into the two large classes of individual or embryonic, and of partial deviations. We have dealt with this division at some length in the previous lecture. It will be apparent at once, if we choose a definite example. Let us ask what is the real significance of the percentage figure of a single plant in sugar beets. This value depends in the first place, on the strain or family from which the beet has been derived, but this primary point may be neglected here, because it is the same for all the beets of any lot, and determines the average, around which all are fluctuating.

The deviation of the percentage figure of a single beet depends on two main groups of external [815] causes. First come those that have influenced the young germs of the plant during its most sensitive period, when still an embryo within the ripening seed. They give a new limitation to the average condition, which once and forever becomes fixed for this special individual. In the second place the young seedling is affected during the development of its crown of leaves, and of its roots, by numerous factors, which cannot change this average, but may induce deviations from it, increasing or decreasing the amount of sugar, which will eventually be laid down in the root. The best young beet may be injured in many ways during periods of its lifetime, and produce less sugar than could reasonably be expected from it. It may be surpassed by beets of inferior constitution, but growing under more favorable circumstances.

Considered from this point of view the result of the polarization test is not a single value, but consists of at least two different factors. It may be equal to the algebraic sum of these, or to their difference, according to whether the external conditions on the field were locally and individually favorable or unfavorable. A large amount of sugar may be due to high individual value, with slight subsequent deviation from it, [816] or to a less prominent character combined with an extreme subordinate deviation.

Hence it is manifest that even the results of such a highly improved technical method do not deserve the confidence usually put in them. They are open to doubt, and the highest figures do not really indicate the best representatives of the race. In order to convey this conception to you in a still stronger manner, let us consider the partial variability as it usually shows itself. The various leaves of a plant may noticeably vary in size, the flowers in color, the fruits in flavor. They fluctuate around an average, which is assumed to represent the approximate value of the whole plant. But if we were allowed to measure only one leaf, or to estimate only one flower or fruit, and be compelled to conclude from it the worth of the whole plant, what mistakes we could make! We might indeed hit upon an average case, but we might as easily get an extreme, either in the way of increase or of decrease. In both cases our judgment would be badly founded. Now who can assure us that the single root of a given beet is an average representative of the partial variability? The fact that there is only one main root does not prove anything. An annual plant has only one stem, but a perennial species has many. The average height of the last is a [817] reliable character, but the casual height of the former is very uncertain.

So it is with the beets. A beet may be divided by its buds and give quite a number of roots, belonging to the same individual. These secondary roots have been tested for the amount of sugar, and found to exhibit a manifest degree of variability. If the first root corresponded to their average, it might be considered as reliable, but if not anyone will grant that an average is more reliable than a single determination. Deviations have as a fact been observed, proving the validity of our assertion. These considerations at once explain the disappointment so often experienced by breeders. Some facts may be quoted from the Belgian professor of agriculture at Gembloux, the late Mr. Laurent. He selected two beets, from a strain, with the exceptional amount of 23% sugar, but kept their offspring separate and analyzed some 60 of each. In both groups the average was only 11-12%, the extremes not surpassing 14-15%. Evidently the choice was a bad one, notwithstanding the high polarization value of the parent. Analogous cases are often observed, and my countrymen, Messrs. Kuhn & Co., go so far as to doubt all excessive variants, and to prefer beets with high, but less extraordinary percentages. Such are to be had in larger numbers [818] and their average has a good chance of exemption from a considerable portion of the doubts adhering to single excessive cases.

It is curious to note here what Louis de Vilmorin taught concerning this point in the year 1850. I quote his own words: "I have observed that in experiments on heredity it is necessary to individualize as much as possible. So I have taken to the habit of saving and sowing separately the seeds of every individual beet, and I have always found that among the chosen parent plants some had an offspring with a better average yield than others. At the end I have come to consider this character only, as a standard for amelioration."

The words are clear and their author is the originator of the whole method of plant breeding selection. Yet the principle has been abandoned, and nearly forgotten under the impression that polarization alone was the supreme guide to be relied upon. However, if I understand the signs rightly, the time is soon coming when Vilmorin's experience will become once more the foundation for progress in breeding.

Leaving the theoretical and historical aspects of the problem, we will now recall the experimental evidence, given in a former lecture, dealing with the inheritance of monstrosities. I have shown that in many instances monstrosities [819] constitute double races, consisting of monstrous and of normal individuals. At first sight one might be induced to surmise that the monstrous ones are the true representatives of the race, and that their seeds should be exclusively sown, in order to keep the strain up to its normal standard. One might even suppose that the normal individuals, or the so-called atavists, had really reverted to the original type of the species and that their progeny would remain true to this.

My experiments, however, have shown that quite the contrary is the case. No doubt, the seeds of the monstrous specimens are trustworthy, but the seeds of the atavists are not less so. Fasciated hawkweeds and twisted teasels gave the same average constitution of the offspring from highly monstrous, and from apparently wholly normal individuals. In other words the fullest development of the visible characteristic was not in the slightest degree an indication of better hereditary tendencies. In unfavorable years a whole generation of a fasciated race may exhibit exclusively normal plants, without transmitting a trace of this deficiency to the following generation. As soon as the suitable conditions return, the monstrosity reassumes its full development. The accordance of these facts with the experience [820] of breeders of domestic animals, and of Louis de Vilmorin, and with the result of the theoretical considerations concerning the factors of fluctuation has led me to suggest the method of selecting, which I have made use of in my experiments with tricotyls and syncotyls.

Seedling variations afford a means of counting many hundreds of individuals in a single germinating pan. If seed from one parent plant is sown only in each pan, a percentage figure for the amount of deviating seedlings may be obtained. These figures we have called the hereditary percentages. I have been able to select the parent plants after their death on the sole ground of these values. And the result has been that from varieties which, on an average, exhibited 50-55% deviating seedlings, after one or two years of selection this proportion in the offspring was brought up to about 90% in most of the cases. Phacelia and mercury with tricotylous seedlings, and the Russian sunflower with connate seed leaves, may be cited as instances.

Besides these tests, others were performed, based only on the visible characters of the seedlings. The result was that this characteristic was almost useless as a criterion. The atavists gave, in the main, nearly the same hereditary percentages as the tricotyls and syncotyls, and [821] their extremes were in each case far better constituted than the average of the chosen type. Hence, for selection purposes, the atavists must be considered to be in no way inferior to the typical specimens.

If it had been possible to apply this principle to twisted and fasciated plants, and perhaps even to other monstrosities, I think that it will readily be granted that the chance of bringing even these races up to a percentage of 90% would have been large enough. But the large size of the cultures required for the counting of numerous groups of offspring in the adult state has deterred me from making such trials. Recently however, I have discovered a species, Viscaria oculata which allows of counting twisted specimens in the pans, and I may soon be able to obtain proofs of this assertion. The validity of the hereditary percentage as a standard of selection has, within the last few years, been recognized and defended by two eminent breeders, W.A. Hays in this country and Von Lochow in Germany. Both of them have started from the experience of breeders of domestic animals. Von Lochow applied the principle to rye. He first showed how fallacious the visible characters often are. For instance the size of the kernels is often dependent on their number in the head, and if this number is [822] reduced by the injurious varietal mark of lacunae (Luckigkeit), the whole harvest will rapidly deteriorate by the selection of the largest kernels from varieties which are not quite free from this hereditary deficiency.

In order to estimate the value of his rye plants, he gathers the seed of each one separately and sows them in rows. Each row corresponds to a parent plant and receives 200 or 150 seeds, according to the available quantity. In this way from 700 to 800 parent plants are tested yearly. Each row is harvested separately. The number of plants gives the average measure of resistance to frost, this being the only important cause of loss. Then the yield in grain and straw is determined and calculated, and other qualities are taken into consideration. Finally one or more groups stand prominent above all others and are chosen for the continuation of the race. All other groups are wholly excluded from the "elite," but among them the best groups and the very best individuals from lesser groups are considered adequate for further cultivation, in order to produce the commercial product of the race.

As a matter of fact the rye of Von Lochow is now one of the best varieties, and even surpasses the celebrated variety of Schlanstedt. It was only after obtaining proof of the validity [823] of his method that Von Lochow decided to give it to the public.

W.M. Hays has made experiments with wheat at the Minnesota Agricultural Experiment Station. He chose a hundred grains as a proper number for the appreciation of each parent plant, and hence has adopted the name of "centgener power" for the hereditary percentage.

The average of the hundred offspring is the standard to judge the parent by. Experience shows at once that this average is not at all proportional to the visible qualities of the parent. Hence the conclusion that the yield of the parent plant is a very uncertain indication of its value as a parent for the succeeding generation. Only the parents with the largest power in the centgener of offspring are chosen, while all others are wholly discarded. Afterwards the seeds of the chosen groups are propagated in the field until the required quantities of seed are obtained.

This centgener power, or breeding ability, is tested and compared for the various parent plants as to yield, grade, and percentage of nitrogenous content in the grain, and as to the ability of the plant to stand erect, resist rust, and other important qualities. It is evident that by this test of a hundred specimens a far better [824] and much more reliable determination can be made than on the ground of the minutest examination of one single plant. From this point of view the method of Hays commands attention. But the chief advantage lies in the fact that it is a direct proof of that which it is desired to prove, while the visible marks give only very indirect information.

Thus the results of the men of practice are in full accordance with those of theory and scientific experiment, and there can be little doubt that they open the way for a rapid and important improvement. Once attained, progress however, will be dependent on the selection principle, and the hereditary percentage, or centgener power or breeding ability, must be determined in each generation anew. Without this the race would soon regress to its former condition.

To return to our starting point, the comparison of artificial and natural selection. Here we are at once struck by the fact that it is hardly imaginable, how nature can make use of this principle. In some measure the members of the best centgener will manifestly be at an advantage, because they contain more fit specimens than the other groups. But the struggle for existence goes on between individuals, and not between groups of brethren against groups of [825] cousins. In every group the best adapted individuals will survive, and soon the breeding differences between the parents must vanish altogether. Manifestly they can, as a rule, have no lasting result on the issue of the struggle far existence.

If now we remember that in Darwin's time this principle, breeding ability, enjoyed a far more general appreciation than at present, and that Darwin must have given it full consideration, it becomes at once clear that this old, but recently revived principle, is not adequate to support the current comparison between artificial and natural selection.

In conclusion, summing up all our arguments, we may state that there is a broad analogy between breeding selection in the widest sense of the word, including variety testing, race improvement and the trial of the breeding ability on one side, and natural selection on the other. This analogy however, points to the importance of the selection between elementary species, and the very subordinate role of intraspecific selection in nature. It strongly supports our view of the origin of species by mutation instead of continuous selection. Or, to put it in the terms chosen lately by Mr. Arthur Harris in a friendly criticism of my views: "Natural selection may explain the survival [826] of the fittest, but it cannot explain the arrival of the fittest."



A

_Abies concolor fastigiata_, 618 _Acacia_, 176, 196, 217, 458, 697 bastard, 343, 617, 618, 664, 665, 666 _Acer compestre nanum_, 612 _Achillea millefolium_, 131, 132, 441 Adaptation, 702 double, 430, 451, 452, 454, 455, 457, 458, 642 _Aegilops ovata_, 265 _speltaeformis_, 265 _Agave vivipara_, 684 _Ageratum coeruleum_, 612 _Agrostemma Coronaries bicolor_, 125 _Githago_, 282 _nicaeensis_, 162 _Agrotis_, 204 Alder, cut-leaved, 147, 596 Alfalfa, 264 Algae, 699 Allen, Grant, 237 _Alliaria_, 638 _Alnus glutinosa laciniata_, 615 Alpine plants, 437, 695, 794 _Althaea_, 490 Amaranth, 282, 452 _Amaranthus caudatus_, 282 _Amaryllis_, 272, 275, 762 brasiliensis_, 275 leopoldi_, 275 pardina_, 275 psittacina_, 275 vittata_, 275 Amen-Hotep, 697 _Ampelopsis_, 239 _Amygdalus persica laevis_, 126 _Anagallis arvensis_, 162 _Androsace_, 634 _Anemone_, 266, 331 _coronaria_, 241, 491 var. "Bride," 510 _magellanica_, 266 _sylvestris_, 266 _Anemone_, garden, 241 Annee, 760 Anomalies, taxonomic, 658, 685 _Anthemis_, 236 _nobilis_, 130 _Anthurium scherzerianum_, 639 _Antirrhinum majus_, 315 _luteum rubro-striatum_, 315 Apetalous flowers, 622 Apples, 134, 240, 328, 454, 806 elementary species, 75 method of cultivating, 76 origin of cultivated varieties, 73 use by the Romans, 74 "Wealthy," 78, 79 wild, 73, 74, 75, 76 _Aquilegia chrysantha_, 161 _Arabis ciliata glabrata_ _hirsuta glaberrima_, 126 _Aralia crassifolia_, 662 Arbres fruitiers ou Pomonomie belge, 76 _Aralia papyrifera_, 662 Arctic flora, 695 _Arnica_, 494 _montana_, 236 Aroids, 222, 631, 639 Artemisias, 131 Artificial selection, 18, 71, 77, 93, 95, 743, 744, 798, 826 first employed, 72, 92 nature of, 19 _Arum maculatum immaculatum_, 125 Ascidia, 310, 366, 367, 427, 428, 669, 670, 671, 672, 673, 674, 675 Ash, 135, 341 one-bladed, 666, 667 weeping, 196, 596 Ashe, 343 Aster, 132, 152, 242 seashore, 200, 282 _Aster Tripolium_, 132, 200, 236, 282, 410 _Astragalus alpinus_, 696 Atavism, 154, 170, 172, 175, 176, 178, 182, 185, 187, 188, 198, 220, 222, 226, 235, 344, 354, 399, 405, 411, 660, 661 bud, 183, 226 definition of, 170, 631 false, 185, 187 negative, 344 positive, 344 seed, 176 systematic, 174, 222, 630-657 Atavists, 156, 201 heredity of, 412 _Atropa Belladonna lutea_, 592 _Aubretia_, 241 _Avena fatua_, 100, 207 _Azalea_, 178, 322 _Azolla caroliniana_, 239

B

Babington, Manual of British Botany, 36, Bailey, 78, 306, 684 Balsams, 334 Bananas, 90, 134 Banyan, 244 Barberry, 133, 180 European, 270 purple, 596 Barbarea vulgaris, 427 Barley, 98, 105, 133, 203, 678, 679 "Nepaul," 203, 676, 677, 679, 681, 682 Bastard-acacia, 133, 136, 140 Bateson, 250 Bauhin, Caspar, 72, 610 Baumann, 618 Beans, 90, 152, 327, 727, 735 Bedstraw, 648 Beech, 133, 135, 242 cut-leaved, 179, 196, 616 laciniated, 196 oak-leaved, 595 purple, 196, 593, 595 Beeches, 427 fern-leaved, 147 Beets, 68, 72, 92, 93, 792, 796, 801, 815, 817, 818 Californian, 796 European, 796 forage, 71, 72, 791 salad, 71 Beet-sugar, 67, 68, 69, 70, 71, 109, 165, 717, 791, 807, 813, 814 Begonia, 218, 366, 509, 765 ever-flowering, 148 tuberous, 272 clarkii, 272 davisii, 272 rosiflora, 272 sedeni, 273 semperflorens, 133, 148, 620 Begonia bulbous, 372 veitchi, 272 Behrens, 804 Belladonna, 145 Bellis perennis, 236 perennis plena, 195 Bentham, 237 Bentham & Hooker, Handbook of British Flora, 36 Berberis, 133, 180, 455 ilicifolia, 270 vulgaris, 270 Bertin, 596 Berula angustifolia, 457 Bessey, 660 Beta maritima, 69 patula, 69, 70 vulgaris, 69, 70 Betula, 132 Between-race, 358 Bewirkung, Theorie der directen (Nageli), 448 Biastrepsis, 402 Bidens, 131 atropurpurea, 131 cernua, 131, 158 leucantha, 131 tripartite, 131 Bilberries, 577 Bindweed, 41924 Binomium, of Newton, 767 Birch, 133, 243 cut-leaved, 596, 616 fastigiate, 618 fern-leaved, 179 Bisoutella, 282 laevigata glabra, 125 Bitter-sweet, 125 Blackberry, 268, 768 "Paradox," 769 Blue-bells, variation in, 54, 491, 577 Blueberries, 769 Blue-bottle, 499, 507, 509, 510 Blueflag, atavism of, 172 Boehmeria, 675 bilboa, 685 Bonnier, 439, 441, 442, 444, 451, 795 Boreau, 663 Brambles, 126, 127, 147, 239, 244, 245, 268, 740, 769, 663 Brassica, 244 Braun, 738 Braun and Schimper, 494 Bread-fruits, 90 Briot, 618 Britton and Brown's Flora, 162 Brooks, 711 Broom, 140 prickly, 217 Broom-rape, 220 Broussonetia papyifera dissecta, 616 Brunella, 146, 268 vulgaris, 577 vulgaris alba, 201 Bryophyllum calycinum, 218 Buckwheat, 452 Bud-variation, 750 Buds, adventitious, 218 Burbank, Luther, 57, 79, 116, 134, 268, 758, 768, 769, 784 Buttercup, 331, 357, 410, 725, 740 Asiatic, 241

C

Cabbages, 428, 684 atavism in, 638 origin of varieties, 621 Cactuses, 444 Cactus-dahlia, 625 Calamintha Acinos, 437, 452 Calamus root, 222 Calendula officinalis, 502 Calliopsis tinctoria, 195 Calluna, 146 vulgaris, 437, 577 Caltha, 490 palustris, 331 Camelina, 684 Camellia, 178, 323 japonica, 368 Camellias, 331 Camomile, 130, 132, 156, 366, 494, 503, 509, 512 Campanula persicifolia, 151, 234 rotundifolia, 437 Campion, 283, 302, 304 evening, 281 red, 238 Canna, 751, 759, 761 indica, 760 "Madame Crozy," 760, 761 nepalensis, 760 warczewiczii, 760 Capsella Bursa-pastoris apetala, 585 heegeri, 22, 582, 583, 684 Carex, 53 Carnation, 178, 241, 491 wheat-ear, 227 Carpinus Betulus heterophylla, 180 Carriere, 491, 596, 612, 806 Carrots, 806 Catch-fly, 419 Carboniferous period, 699 Casuarina quadrivalvis, 649 Cauliflowers, origin of, 621 Caumzet, 614 Causation, theory of direct, (Nageli), 448 Cedar, pyramidal, 618 Celandine, 147, 245, 280, 365 oak-leaved, 603, 610, 611 Celosia, 621 Celosia cristata, 327, 411 Centaurea, 242 Centgener power, 20, 822 Centranthus macrosiphon, 424 Cephalotaxus, 170, 226 pedunculata fastigiata, 169 Cereals, 105, 106, 107, 119, 801, 804 origin of cultivation, 104 Character-units, 632 Charlock, 424 Cheiranthus, 490 Cheiri, 370 Cheiri gynantherus, 371 Chelidonium laciniatum, 22, 609 majus, 147, 365, 600, 610, 611 majus foliis quernis, 610 Cherries, 79 Cherry, bird's, 617 Chestnuts, 427 Chromosomes, 306 Chrysanthemum, 178, 274 corn, 739 Chrysanthemum carinatum, 494 coronarium, 161, 202, 510 grandiflorum, 739 imbricatum, 494 indicum, 490 inodorum, 503 inodorum plenissimum, 336 new double, 501 segetum, 202, 493, 504, 729 segetum, var. grandiflorum, 43, 495, 498, 504, 504 Chrysopogon montanus, 450 Cieslar, 804 Cineraria cruenta, 514 Cinquefoil, 52 Clarkia, 420 elegans, 198 pulchella, 282 pulchella carnea, 162 Clematis Vitalba, 662 Viticella nana, 612 Clover, 80, 102, 674 crimson (Italian), 353, 358, 359, 360 five-leaved, 340, 362, 374, 431, 509, 789 four-leaved, 340, 346, 352 red, 235, 281 white, 133, 366 Clusius, 610 Cochlearia anglica, 52 danica, 52 officinalis, 52 Coconut, 67, 82, 83, 87, 88, 89 dispersal of, 85, 89 geographic origin of, 88,89 Coconut-palm, 84, 88 Cockerell, T.D.A., 139, 140, 591 Cocklebur, 139 Cockscomb, 165, 327, 356, 411, 621 Cocos nucifera stupposa, 83, 84 cupuliformis, 82 rutila, 82 Codiaeum appendicularum, 673 Colchicum, 490 Coleus, 132 Columbine, 725 yellow, 161 Columbus, 89, 118 Columella, 106 Composites, 130, 131, 336, 723, 778 Conifers, 168, 226, 239, 455 weeping, 617 Connation, of petals, 660, 661 "Conquests," 242 Contra-selection, 425 Cook, 84, 86, 88, 89 Corn, 81, 90, 118, 119, 135, 283, 287, 288, 775, 786, 788, 804 American, 205 Corn-cockle, 162 Corn-chrysanthemum, 739 Corn-flowers, 491, 92 Corn, "Forty-day," 118 "Harlequin," 327 sterile variety of, 622 sugar, 135, 158 "Tuscarora," 205 Corn-marigold, 493, 494 Cornel berry, yellow, 196 Cornaceae, 675 Cornu, 338 Cornus Mas, 196 Correlation, 142 Corylus, 133 Avellana, 181 tubulosa, 181 Cotton, 725 Cotyledon, 674 variation in, 416 Crambe maritima, 621 Cranesbill, 599 European, 628 meadow, 322 Crataegus, 196 oxyacantha, 132 Crowfoot, 331 corn, 283 Crepis biennis, 410, 411 Cress, Indian, 192 Crosses bisexual, 255, 276, 294, 298 reciprocal, 279 unisexual, 255, 261 varietal (see Hybrids) Croton, 673, 674 Crozy, 760, 762 Crucifers, 222, 635 Cryptomeria, 169, 226 japonica, 239 Cucumbers, 118 Cucumis, 52 Cucurbita, 52 Cultivated plants, 65, 66 elementary species of, 62 improvement of, 92 mixed nature of, 96, 118 origin of, 91 Currants, 79 Californian, 270 flowering, 166 "Gordon's," 270 Missouri, 270 white, 158 white-flowered, 167 Cuttings, 721 Cyclamen, 323, 355, 627, 684 Butterfly, 627 vernum, 619 Cypripedium caudatum, 487 Cytisus adami, 271 candicans Attleyanus, 367 Laburnum, 271 prostratus, 139 prostratus ciliata, 125 purpureus, 271 spinescens, 139

D

_Dahlia_, 131, 241, 272, 625 cactus, 625 "Jules Chretien," 628 purple-leaved, 626 "surprise," 230 tubular, 627 [sic] 274, 490, 764 first double ones, 490 green, 227, 229, 230 Daisies, 131, 132, 494 double, 195 hen-and-chicken, 514 ox-eye, 202 Shasta, 769 yellow, 202 Dandelion, 411 parthenogenesis, 61 variations in, 60 Daphne Mezereum, 146 Darwin, 1, 2, 3, 4, 5, 6, 7, 18, 76, 85, 93, 109, 110, 180, 196, 205, 206, 242, 306, 324, 338, 448, 571, 604, 612, 689, 702, 710, 715, 743, 798, 825 Darwin, George, 711 Darwinian theory, 461 basis of, 5 Date, 134 _Datura Stramonium_, 139, 142 _Stramonium inermis_, 300 _Tatula_, 139, 142, 300 Dead-nettle, 237 De Bary, 38, 47, 49 De Candolle, 76, 84, 85, 89, 228, 370, 403, 621 Alphonse, 74, 129, 226 A.P., 129 Casimir, 659, 676 De Graaff, 275 _Delphinium Ajacis_, 192 Deniau, 617 Descent, theory of, 690, 694, 702, 707, 716, 798 De Serres, Olivier, 72 _Desmodium gyrans_, 655, 656, 663, 664, 65 Dewberry, California, 269 _Dianthus barbatus_, 322, 648 twisted variety, 408 Diatoms, 699 Dictoyledons ancestors of monocotyledons, 15 _Digitalis parviflora_, 161, 640 _purpurea_, 483 pelorism of, 482 Dimorphism, 445, 447, 454, 457, 458 Dippe, 810 _Dipsacus fullonum_, 402 sylvestris_, 402, 402 Dominant character, 280 Double flowers poppies 490 production of, 489 types of, 330 Double races (see also ever-sporting varieties), 419, 427, 428 Dubois, Eugene, 712 Duchesne, 185, 188, 596 Duckweed, 222 _Draba_, 692, 693 verna, 47, 50, 51, 53, 125, 126, 518, 533, 546, 547, 561 _Dracocephalum moldavicum_, 419 Dragon-head, 419 _Drosera anglica_, 268 _filiformis_, 268 _intermedia_, 268 _obovata_, 267 _rotundifolia_, 268

E

Earth, age of, 710 Edelweiss, 438 Eichler, 660 Election, 801 Electric light, growth in, 442 Elementary species, 11, 13, 32, 67, 74, 76, 77, 78, 79, 91, 95, 116, 119, 124, 126, 128, 129, 207, 238, 252, 256, 307, 430, 435, 695, 696, 698, 702, 715, 787, 798, 800, 825 apples, 75 coconut, 82 corn, 81 cultivated plants, 62 definition of, 12, 35, 127 flax, 80 how produced, 16, 248 hybrids of, 253, 255 mutation of, 141 origin of, 459, 603 origin of, how studied, 463 selection of, 92 varieties vs., 14, 15, 141, 152, 224, 243, 247, 251, 495 Elm, 136, 219, 239, 427 _Epilobium_, 268 _hirsutum_, 683 _hirsutum cruciatum_, 588 _montanum_, 269 _tetragonum_, 269 _Equisetum Telmateja_, 642, 649 _Erica Tetralix_, 577, 661 Ericaceae, 146, 660 _Erigeron _Asteroides_, 450 _canadensis_, 132, 236, 453, 600, 695 _Erodium_, 146 _cicutarium album_, 161 _Erucastrum_, 630, 638, 639 _pollichii_, 222, 637 _Eryngium campestre_, 674 _maritimum_, 674 _Erysimum cheiranthoides_, 638 _Erythraea pulchella_, 452 _Erythrina_, 621 _Crista-galli_, 620 Eschcholtzias, 59 Esimpler, 337 _Eucalyptus citriodora_, 669 _Globulus_, 217 _Euphorbia Ipecacuanha_, 55 Evening-primrose, 62, 204, 256, 424, 686, 687, 688, 690, 691, 694, 695, 699, 702, 703, 705, 707, 708, 713, 747, 793 Evolution, 93, 685, 686, 689, 704, 707, 709, 710, 713, 718 degressive, 222, 223, 249 progression in, 630 progressive, 221, 222, 223, 248 regression in, 630 regressive, 221, 222; 223, 24 retrograde, 221, 631 Extremes, asexual multiplication of, 742, 769

F

Fabre, 265 Fagus, 133 Fagus sylvatica pectinata, 179 Fan, genealogical, 700 Fasciated stems, 409, 412 Ferns, 63 cristate, 427 plumose, 427 Ficaria, 53 Ficus radicans, 436 religiosus, 244 repens, 436 stipulata, 436 ulmifolia, 436 Figs, 436 Filago, 52 Fir, 134, 804 Fittest, survival of, 826 Flax, 80, 805 springing, 80 threshing, 80 white-flowered, 158, 160 Fleabane, Canada, 132, 236 Flowers, gamopetalous, 660 Fluctuability embryonic, see Fluctuation, individual Fluctuation, 708, 715, 716, 718, 719, 724, 737, 741 curves of, 729, 794 defined, 191 individual, 718, 723, 732, 741, 745, 749, 788 mutation vs. 7, 16, 719 partial, 718, 723, 732, 741, 745, 748, 749, 771 inadequate for evolution, in elementary species, 19 nature of, 18 specific and varietal characters vs. 17 Forget-me-not, 368 Fothergill, John, 521 Foxglove, 163 peloric, 164, 356, 367 yellow, 161, 640 Fraxinus excelsior monophylla, 667 exheterophylla, 667 simplici folio, 667 French flora (Grenier and Godron), 433 Fries on Hieracium, 60 Frostweed, 440 species of, 52 Fuchsia, 272, 355 Fuchsias, 491

G

Gaertner, 279 Galeopsis Ladanum canescens, 139 Galium, 648 Aparine, 409, 648 elatum, 52 erectum, 52 Mollugo, 62 verum, 648 Gallesio, 138 Galton, 736, 776 Gamopetaly, 662 Garden-pansy, origin of, 38 Garlic, 638 Gauchery, 452 Geikie, 711 Genera artificial character of, 36 polymorphous, 692 Gentiana punctata concolor, 125 Gentians, 577 Georgics (Vergil), 106 Geranium pratense, 323, 628 album, 628 pyreniacum, 599 German flora (Koth), 432 Geum, 282 Gherkins, 118 Gideon, Peter M., 78 Glacial period, 696 Gladiolus, 241, 272, 274, 368, 765 cardinalis, 275 gandavensis, 275 psittacinus, 275 purpureo-auratus, 275 Glaucium, 241 Gleditschia sinensis, 614 triacanthos pendula, 617 Gloxinia, 282, 485 erect, 626 Gloxinia erecta, 485 peloric variety, 485 Gnaphalium Leontopodium, 438 Godetia amoena, 161 Godetias, 59, 232 Godron, 265, 432 Goeppert, 370 Gooseberry, 79, 140, 626 red, 133, 165, 241 Grapes, 90, 158, 328 Grape-hyacinth, plumosa, 134 Grasses, 102, 631, 681 Grenier, 433 Groundsel, 132 Growth, nutrition and, 714, 720, 722 Guelder-rose, 134, 239 Gum-tree, Australian, 217 Gypsophila paniculata twisted variety, 409

H

Haeckel, 707 Half-races, 358, 372, 409, 419, 424, 427, 428 Hall, 444 Hallet, F.F., 109 Harebell, 232 peach-leaved, 234 Harris, Arthur, 825 Harshberger, John W., 591 on _Euphorbia_ in New Jersey, 55 Hawksbeard, 410, 411, 412 Hawkweed, 411, 439, 443, 819 Hawkweeds seeding without fertilization, 61 Hawthorn, white, 132 Hays, W.M. on individual selection, 20, 94, 95, 117, 821, 823, 824 Hazelnut, 133, 181, 242 Hazels, cut-leaved, 596,-616 Heath family, 146, 222, 660 Heaths, origin of, 662 Heather, 577 _Hedera Helix arborea_, 437 Hedgehog burweed, 140 _Hedys_Arum_, 664 Heeger, 582 Heer, Oswald, 74, 105 Heinricher, 172, 173, 174 _Helianthemum_, 53, 125, 126, 561 _apenninum_, 52 _pilosum_, 52 _polifolium_, 52 _pulverulentum_, 52 _vulgare_, 440 _Helichrysum_, 420 _Helwingia_, 678, 678, 682 _rusciflora_, 675 Hemp, 419 Henbane, 282 _Hepatica_, 322, 490 Heredity, 731, 734, 818 bearers of, 632 in teasels, 642 _Hesperis_, 241, 322 _matronalis_, 323, 411 _Heylandia latebrosa_, 450 _Hibiscus Moscheutos_, 591 _Hieracium_, 59, 439 _alpinum_, 696 Hildebrand, 160, 240, 241 Hoffman, 160, 662 Hofmeister, 160, 370, 480 Holbein, 164, 596 Holly, 140, 196 Holtermann, 449, 451 Hollyhock, 427 Honeysuckle, 674 ground, 443 _Hordeum distichum_, 677 _hexastichum_, 677, 678 _tetrastichum_, 677 _trifurcatum_, 676, 678 _vulgare trifurcatum_, 203 Hornbeam, European, 180 Horse-chestnut, 219 thornless, 234 Horsetail, Canadian, 695 European, 649 Horsetail, family, 641 Horse-weed, 132 Canadian, 452 _Hortensia_, 134, 181 Horticulture, mutations in, 604 Houseleek, 370, 371 Hunneman, John, 521 Hyacinths, 178, 322 white, 160 Hybrids, 58, 201, 202, 206, 250, 575 between elementary species, 253 constant, 263, 264, 265, 266, 267, 268, 269 law of varietal, 716 Mendelian, 324 nature of, 20 species, 256, 260 splitting of, 210 varietal, 208, 209, 247, 277, 278, 279, 281, 285, 293, 294 Hybridization, 706, 751, 752, 758, 759, 764 _Hydrocotyle_, 668 _Hyoscyamus niger_, 282 _pallidus_, 283 _Hypericum perforatum_, 725 _Hyssopus officinalis_, 161