The simpler brown seaweeds, so far as known, multiply only by means of zooespores, which may grow directly into new plants, or, as has been observed in some species, two zooespores will first unite. A few, like Ectocarpus (Fig. 28, A), are simple, branched filaments, but most are large plants with complex tissues. Of the latter, a familiar example is the common kelp, "devil's apron" (Laminaria), often three to four metres in length, with a stout stalk, provided with root-like organs, by which it is firmly fastened. Above, it expands into a broad, leaf-like frond, which in some species is divided into strips. Related to the kelps is the giant kelp of the Pacific (Macrocystis), which is said sometimes to reach a length of three hundred metres.



The highest of the class are the gulf weeds (Sargassum), plants of the warmer seas, but one species of which is found from Cape Cod southward (Fig. 28, D, E). These plants possess distinct stems and leaves, and there are stalked air bladders, looking like berries, giving the plant a striking resemblance to the higher land plants.



CHAPTER VII.

CLASS III.—THE RED ALGAE (Rhodophyceae).

These are among the most beautiful and interesting members of the plant kingdom, both on account of their beautiful colors and the exquisitely graceful forms exhibited by many of them. Unfortunately for inland students they are, with few exceptions, confined to salt water, and consequently fresh material is not available. Nevertheless, enough can be done with dried material to get a good idea of their general appearance, and the fruiting plants can be readily preserved in strong alcohol. Specimens, simply dried, may be kept for an indefinite period, and on being placed in water will assume perfectly the appearance of the living plants. Prolonged exposure, however, to the action of fresh water extracts the red pigment that gives them their characteristic color. This pigment is found in the chlorophyll bodies, and usually quite conceals the chlorophyll, which, however, becomes evident so soon as the red pigment is removed.

The red seaweeds differ much in the complexity of the plant body, but all agree in the presence of the red pigment, and, at least in the main, in their reproduction. The simpler ones consist of rows of cells, usually branching like Cladophora; others form cell plates comparable to Ulva (Fig. 30, C, D); while others, among which is the well-known Irish moss (Chondrus), form plants of considerable size, with pretty well differentiated tissues. In such forms the outer cells are smaller and firmer, constituting a sort of rind; while the inner portions are made up of larger and looser cells, and may be called the pith. Between these extremes are all intermediate forms.

They usually grow attached to rocks, shells, wood, or other plants, such as the kelps and even the larger red seaweeds. They are most abundant in the warmer seas, but still a considerable number may be found in all parts of the ocean, even extending into the Arctic regions.



The methods of reproduction may be best illustrated by a specific example, and preferably one of the simpler ones, as these are most readily studied microscopically.

The form here illustrated (Callithamnion) grows attached to wharves, etc., below low-water mark, and is extremely delicate, collapsing completely when removed from the water. The color is a bright rosy red, and with its graceful form and extreme delicacy it makes one of the most beautiful of the group.

If alcoholic material is used, it may be mounted for examination either in water or very dilute glycerine.

The plant is composed of much-branched, slender filaments, closely resembling Cladophora in structure, but with smaller cells (Fig. 29, B). The non-sexual reproduction is by means of special spores, which from being formed in groups of four, are known as tetraspores. In the species under consideration the mother cell of the tetraspores arises as a small bud near the upper end of one of the ordinary cells (Fig. 29, C i). This bud rapidly increases in size, assuming an oval form, and becoming cut off from the cell of the stem (Fig. 29, C ii). The contents now divide into four equal parts, arranged like the quadrants of a sphere. When ripe, the wall of the mother cell gives way, and the four spores escape into the water and give rise to new plants. These spores, it will be noticed, differ in one important particular from corresponding spores in most algae, in being unprovided with cilia, and incapable of spontaneous movement.

Occasionally in the same plant that bears tetraspores, but more commonly in special ones, there are produced the sexual organs, and subsequently the sporocarps, or fruits, developed from them. The plants that bear them are usually stouter that the non-sexual ones, and the masses of ripe carpospores are large enough to be readily seen with the naked eye.

If a plant bearing ripe spores is selected, the young stages of the female organ (procarp) may generally be found by examining the younger parts of the plant. The procarp arises from a single cell of the filament. This cell undergoes division by a series of longitudinal walls into a central cell and about four peripheral ones (Fig. 29, D i). One of the latter divides next into an upper and a lower cell, the former growing out into a long, colorless appendage known as a trichogyne (Fig. 29, D, tr.).

The antheridia (Fig. 29, E) are hemispherical masses of closely set colorless cells, each of which develops a single spermatozoid which, like the tetraspores, is destitute of cilia, and is dependent upon the movement of the water to convey it to the neighborhood of the procarp. Occasionally one of these spermatozoids may be found attached to the trichogyne, and in this way fertilization is effected. Curiously enough, neither the cell which is immediately fertilized, nor the one beneath it, undergo any further change; but two of the other peripheral cells on opposite sides of the filament grow rapidly and develop into large, irregular masses of spores (Fig. 29, D III, IV).

While the plant here described may be taken as a type of the group, it must be borne in mind that many of them differ widely, not only in the structure of the plant body, but in the complexity of the sexual organs and spores as well. The tetraspores are often imbedded in the tissues of the plant, or may be in special receptacles, nor are they always arranged in the same way as here described, and the same is true of the carpospores. These latter are in some of the higher forms, e.g. Polysiphonia (Fig. 29, F), contained in urn-shaped receptacles, or they may be buried within the tissues of the plant.



The fresh-water forms are not common, but may occasionally be met with in mill streams and other running water, attached to stones and woodwork, but are much inferior in size and beauty to the marine species. The red color is not so pronounced, and they are, as a rule, somewhat dull colored.



The commonest genera are Batrachospermum and Lemanea (Fig. 31).



CHAPTER VIII.

SUB-KINGDOM III.

FUNGI.

The name "Fungi" has been given to a vast assemblage of plants, varying much among themselves, but on the whole of about the same structural rank as the algae. Unlike the algae, however, they are entirely destitute of chlorophyll, and in consequence are dependent upon organic matter for food, some being parasites (growing upon living organisms), others saprophytes (feeding on dead matter). Some of them show close resemblances in structure to certain algae, and there is reason to believe that they are descended from forms that originally had chlorophyll; others are very different from any green plants, though more or less evidently related among themselves. Recognizing then these distinctions, we may make two divisions of the sub-kingdom: I. The Alga-Fungi (Phycomycetes), and II. The True Fungi (Mycomycetes).

CLASS I.—Phycomycetes.

These are fungi consisting of long, undivided, often branching tubular filaments, resembling quite closely those of Vaucheria or other Siphoneae, but always destitute of any trace of chlorophyll. The simplest of these include the common moulds (Mucorini), one of which will serve to illustrate the characteristics of the order.

If a bit of fresh bread, slightly moistened, is kept under a bell jar or tumbler in a warm room, in the course of twenty-four hours or so it will be covered with a film of fine white threads, and a little later will produce a crop of little globular bodies mounted on upright stalks. These are at first white, but soon become black, and the filaments bearing them also grow dark-colored.

These are moulds, and have grown from spores that are in the atmosphere falling on the bread, which offers the proper conditions for their growth and multiplication.

One of the commonest moulds is the one here figured (Fig. 32), and named Mucor stolonifer, from the runners, or "stolons," by which it spreads from one point to another. As it grows it sends out these runners along the surface of the bread, or even along the inner surface of the glass covering it. They fasten themselves at intervals to the substratum, and send up from these points clusters of short filaments, each one tipped with a spore case, or "sporangium."

For microscopical study they are best mounted in dilute glycerine (about one-quarter glycerine to three-quarters pure water). After carefully spreading out the specimens in this mixture, allow a drop of alcohol to fall upon the preparation, and then put on the cover glass. The alcohol drives out the air, which otherwise interferes badly with the examination.

The whole plant consists of a very long, much-branched, but undivided tubular filament. Where it is in contact with the substratum, root-like outgrowths are formed, not unlike those observed in Vaucheria. At first the walls are colorless, but later become dark smoky brown in color. A layer of colorless granular protoplasm lines the wall, becoming more abundant toward the growing tips of the branches. The spore cases, "sporangia," arise at the ends of upright branches (Fig. 32, C), which at first are cylindrical (a), but later enlarge at the end (b), and become cut off by a convex wall (c). This wall pushes up into the young sporangium, forming a structure called the "columella." When fully grown, the sporangium is globular, and appears quite opaque, owing to the numerous granules in the protoplasm filling the space between the columella and its outer wall. This protoplasm now divides into a great number of small oval cells (spores), which rapidly darken, owing to a thick, black wall formed about each one, and at the same time the columella and the stalk of the sporangium become dark-colored.

When ripe, the wall of the sporangium dissolves, and the spores (Fig. 32, E) are set free. The columella remains unchanged, and some of the spores often remain sticking to it (Fig. 32, D).



Spores formed in a manner strongly recalling those of the pond scums are also known, but only occur after the plants have grown for a long time, and hence are rarely met with (Fig. 32, I).

Another common mould (M. mucedo), often growing in company with the one described, differs from it mainly in the longer stalk of the sporangium, which is also smaller, and in not forming runners. This species sometimes bears clusters of very small sporangia attached to the middle of the ordinary sporangial filament (Fig. 32, F, H). These small sporangia have no columella.

Other moulds are sometimes met with, parasitic upon the larger species of Mucor.

Related to the black moulds are the insect moulds (Entomopthoreae), which attack and destroy insects. The commonest of these attacks the house flies in autumn, when the flies, thus infested, may often be found sticking to window panes, and surrounded by a whitish halo of the spores that have been thrown off by the fungus.

ORDER II.—WHITE RUSTS AND MILDEWS (Peronosporeae)

These are exclusively parasitic fungi, and grow within the tissues of various flowering plants, sometimes entirely destroying them.

As a type of this group we will select a very common one (Cystopus bliti), that is always to be found in late summer and autumn growing on pig weed (Amarantus). It forms whitish, blister-like blotches about the size of a pin head on the leaves and stems, being commonest on the under side of the leaves (Fig. 33, A). In the earlier stages the leaf does not appear much affected, but later becomes brown and withered about the blotches caused by the fungus.

If a thin vertical section of the leaf is made through one of these blotches, and mounted as described for Mucor, the latter is found to be composed of a mass of spores that have been produced below the epidermis of the leaf, and have pushed it up by their growth. If the section is a very thin one, we may be able to make out the structure of the fungus, and then find it to be composed of irregular, tubular, much-branched filaments, which, however, are not divided by cross-walls. These filaments run through the intercellular spaces of the leaf, and send into the cells little globular suckers, by means of which the fungus feeds.

The spores already mentioned are formed at the ends of crowded filaments, that push up, and finally rupture the epidermis (Fig. 33, B). They are formed by the ends of the filaments swelling up and becoming constricted, so as to form an oval spore, which is then cut off by a wall. The portion of the filament immediately below acts in the same way, and the process is repeated until a chain of half a dozen or more may be produced, the lowest one being always the last formed. When ripe, the spores are separated by a thin neck, and become very easily broken off.

In order to follow their germination it is only necessary to place a few leaves with fresh patches of the fungus under a bell jar or tumbler, inverted over a dish full of water, so as to keep the air within saturated with moisture, but taking care to keep the leaves out of the water. After about twenty-four hours, if some of the spores are scraped off and mounted in water, they will germinate in the course of an hour or so. The contents divide into about eight parts, which escape from the top of the spore, which at this time projects as a little papilla. On escaping, each mass of protoplasm swims away as a zooespore, with two extremely delicate cilia. After a short time it comes to rest, and, after developing a thin cell wall, germinates by sending out one or two filaments (Fig. 33, C, E).



Under normal conditions the spores probably germinate when the leaves are wet, and the filaments enter the plant through the breathing pores on the lower surface of the leaves, and spread rapidly through the intercellular spaces.

Later on, spores of a very different kind are produced. Unlike those already studied, they are formed some distance below the epidermis, and in order to study them satisfactorily, the fungus must be freed from the host plant. In order to do this, small pieces of the leaf should be boiled for about a minute in strong caustic potash, and then treated with acetic or hydrochloric acid. By this means the tissues of the leaf become so soft as to be readily removed, while the fungus is but little affected. The preparation should now be washed and mounted in dilute glycerine.

The spores (ooespores) are much larger than those first formed, and possess an outer coat of a dark brown color (Fig. 33, H). Each spore is contained in a large cell, which arises as a swelling of one of the filaments, and becomes shut off by a wall. At first (Fig. 33, F) its contents are granular, and fill it completely, but later contract to form a globular mass of protoplasm (G. o), the germ cell or egg cell. The whole is an ooegonium, and differs in no essential respect from that of Vaucheria.

Frequently a smaller cell (antheridium), arising from a neighboring filament, and in close contact with the ooegonium, may be detected (Fig. 33, F, G, an.), and in exceptionally favorable cases a tube is to be seen connecting it with the germ cell, and by means of which fertilization is effected.

After being fertilized, the germ cell secretes a wall, at first thin and colorless, but later becoming thick and dark-colored on the outside, and showing a division into several layers, the outermost of which is dark brown, and covered with irregular reticulate markings. These spores do not germinate at once, but remain over winter unchanged.



It is by no means impossible that sometimes the germ cell may develop into a spore without being fertilized, as is the case in many of the water moulds.

Closely related to the species above described is another one (C. candidus), which attacks shepherd's-purse, radish, and others of the mustard family, upon which it forms chalky white blotches, and distorts the diseased parts of the plant very greatly.

For some reasons this is the best species for study, longitudinal sections through the stem showing very beautifully the structure of the fungus, and the penetration of the cells of the host[4] by the suckers (Fig. 34).

[4] "Host," the plant or animal upon which a parasite lives.



Very similar to the white rusts in most respects, but differing in the arrangement of the non-sexual spores, are the mildews (Peronospora, Phytophthora). These plants form mouldy-looking patches on the leaves and stems of many plants, and are often very destructive. Among them are the vine mildew (Peronospora viticola) (Fig. 35), the potato fungus (Phytophthora infestans), and many others.

ORDER III.—Saprolegniaceae (WATER MOULDS).

These plants resemble quite closely the white rusts, and are probably related to them. They grow on decaying organic matter in water, or sometimes on living water animals, fish, crustaceans, etc. They may usually be had for study by throwing into water taken from a stagnant pond or aquarium, a dead fly or some other insect. After a few days it will probably be found covered with a dense growth of fine, white filaments, standing out from it in all directions (Fig. 36, A). Somewhat later, if carefully examined with a lens, little round, white bodies may be seen scattered among the filaments.



On carefully removing a bit of the younger growth and examining it microscopically, it is found to consist of long filaments much like those of Vaucheria, but entirely destitute of chlorophyll. In places these filaments are filled with densely granular protoplasm, which when highly magnified exhibits streaming movements. The protoplasm contains a large amount of oil in the form of small, shining drops.

In the early stages of its growth the plant multiplies by zooespores, produced in great numbers in sporangia at the ends of the branches. The protoplasm collects here much as we saw in V. sessilis, the end of the filament becoming club-shaped and ending in a short protuberance (Fig. 36, B). This end becomes separated by a wall, and the contents divide into numerous small cells that sometimes are naked, and sometimes have a delicate membrane about them. The first sign of division is the appearance in the protoplasm of delicate lines dividing it into numerous polygonal areas which soon become more distinct, and are seen to be distinct cells whose outlines remain more or less angular on account of the mutual pressure. When ripe, the end of the sporangium opens, and the contained cells are discharged (Fig. 36, C). In case they have no membrane, they swim away at once, each being provided with two cilia, and resembling almost exactly the zooespores of the white rust (Fig. 36, D, E). When the cells are surrounded by a membrane they remain for some time at rest, but finally the contents escape as a zooespore, like those already described. By killing the zooespores with a little iodine the granular nature of the protoplasm is made more evident, and the cilia may be seen. They soon come to rest, and germinate in the same way as those of the white rusts and mildews.

As soon as the sporangium is emptied, a new one is formed, either by the filament growing up through it (Fig. 36, F) and the end being again cut off, or else by a branch budding out just below the base of the empty sporangium, and growing up by the side of it.

Besides zooespores there are also resting spores developed. Ooegonia like those of Vaucheria or the Peronosporeae are formed usually after the formation of zooespores has ceased; but in many cases, perhaps all, these develop without being fertilized. Antheridia are often wanting, and even when they are present, it is very doubtful whether fertilization takes place.[5]

[5] The antheridia, when present, arise as branches just below the ooegonium, and become closely applied to it, sometimes sending tubes through its wall, but there has been no satisfactory demonstration of an actual transfer of the contents of the antheridium to the egg cell.

The ooegonia (Fig. 36, G, H) arise at the end of the main filaments, or of short side branches, very much as do the sporangia, from which they differ at this stage in being of globular form. The contents contract to form one or several egg cells, naked at first, but later becoming thick-walled resting spores (H).



CHAPTER IX.

THE TRUE FUNGI (Mycomycetes).

The great majority of the plants ordinarily known as fungi are embraced under this head. While some of the lower forms show affinities with the Phycomycetes, and through them with the algae, the greater number differ very strongly from all green plants both in their habits and in their structure and reproduction. It is a much-disputed point whether sexual reproduction occurs in any of them, and it is highly probable that in the great majority, at any rate, the reproduction is purely non-sexual.

Probably to be reckoned with the Mycomycetes, but of doubtful affinities, are the small unicellular fungi that are the main causes of alcoholic fermentation; these are the yeast fungi (Saccharomycetes). They cause the fermentation of beer and wine, as well as the incipient fermentation in bread, causing it to "rise" by the giving off of bubbles of carbonic acid gas during the process.

If a little common yeast is put into water containing starch or sugar, and kept in a warm place, in a short time bubbles of gas will make their appearance, and after a little longer time alcohol may be detected by proper tests; in short, alcoholic fermentation is taking place in the solution.

If a little of the fermenting liquid is examined microscopically, it will be found to contain great numbers of very small, oval cells, with thin cell walls and colorless contents. A careful examination with a strong lens (magnifying from 500-1000 diameters) shows that the protoplasm, in which are granules of varying size, does not fill the cell completely, but that there are one or more large vacuoles or spaces filled with colorless cell sap. No nucleus is visible in the living cell, but it has been shown that a nucleus is present.

If growth is active, many of the cells will be seen dividing. The process is somewhat different from ordinary fission and is called budding (Fig. 37, B). A small protuberance appears at the bud or at the side of the cell, and enlarges rapidly, assuming the form of the mother cell, from which it becomes completely separated by the constriction of the base, and may fall off at once, or, as is more frequently the case, may remain attached for a time, giving rise itself to other buds, so that not infrequently groups of half a dozen or more cells are met with (Fig. 37, B, C).



That the yeast cells are the principal agents of alcoholic fermentation may be shown in much the same way that bacteria are shown to cause ordinary decomposition. Liquids from which they are excluded will remain unfermented for an indefinite time.

There has been much controversy as to the systematic position of the yeast fungi, which has not yet been satisfactorily settled, the question being whether they are to be regarded as independent plants or only one stage in the life history of some higher fungi (possibly the Smuts), which through cultivation have lost the power of developing further.

CLASS I.—THE SMUTS (Ustillagineae).

The smuts are common and often very destructive parasitic fungi, living entirely within the tissues of the higher plants. Owing to this, as well as to the excessively small spores and difficulty in germinating them, the plants are very difficult of study, except in a general way, and we will content ourselves with a glance at one of the common forms, the corn smut (Ustillago maydis). This familiar fungus attacks Indian corn, forming its spores in enormous quantities in various parts of the diseased plant, but particularly in the flowers ("tassel" and young ear).

The filaments, which resemble somewhat those of the white rusts, penetrate all parts of the plant, and as the time approaches for the formation of the spores, these branch extensively, and at the same time become soft and mucilaginous (Fig. 38, B). The ends of these short branches enlarge rapidly and become shut off by partitions, and in each a globular spore (Fig. 38, C) is produced. The outer wall is very dark-colored and provided with short spines. To study the filaments and spore formation, very thin sections should be made through the young kernels or other parts in the vicinity, before they are noticeably distorted by the growth of the spore-bearing filaments.



As the spores are forming, an abnormal growth is set up in the cells of the part attacked, which in consequence becomes enormously enlarged (Fig. 38, A), single grains sometimes growing as large as a walnut. As the spores ripen, the affected parts, which are at first white, become a livid gray, due to the black spores shining through the overlying white tissues. Finally the masses of spores burst through the overlying cells, appearing like masses of soot, whence the popular name for the plant.

The remaining Mycomycetes are pretty readily divisible into two great classes, based upon the arrangement of the spores. The first of these is known as the Ascomycetes (Sac fungi), the other the Basidiomycetes (mushrooms, puff-balls, etc.).

CLASS II.—Ascomycetes (SAC FUNGI).

This class includes a very great number of common plants, all resembling each other in producing spores in sacs (asci, sing. ascus) that are usually oblong in shape, and each containing eight spores, although the number is not always the same. Besides the spores formed in these sacs (ascospores), there are other forms produced in various ways.

There are two main divisions of the class, the first including only a few forms, most of which are not likely to be met with by the student. In these the spore sacs are borne directly upon the filaments without any protective covering. The only form that is at all common is a parasitic fungus (Exoascus) that attacks peach-trees, causing the disease of the leaves known as "curl."

All of the common Ascomycetes belong to the second division, and have the spore sacs contained in special structures called spore fruits, that may reach a diameter of several centimetres in a few cases, though ordinarily much smaller.

Among the simpler members of this group are the mildews (Perisporiaceae), mostly parasitic forms, living upon the leaves and stems of flowering plants, sometimes causing serious injury by their depredations. They form white or grayish downy films on the surface of the plant, in certain stages looking like hoar-frost. Being very common, they may be readily obtained, and are easily studied. One of the best species for study (Podosphaera) grows abundantly on the leaves of the dandelion, especially when the plants are growing under unfavorable conditions. The same species is also found on other plants of the same family. It may be found at almost any time during the summer; but for studying, the spore fruits material should be collected in late summer or early autumn. It at first appears as white, frost-like patches, growing dingier as it becomes older, and careful scrutiny of the older specimens will show numerous brown or blackish specks scattered over the patches. These are the spore fruits.



For microscopical study, fresh material may be used, or, if necessary, dried specimens. The latter, before mounting, should be soaked for a short time in water, to which has been added a few drops of caustic-potash solution. This will remove the brittleness, and swell up the dried filaments to their original proportions. A portion of the plant should be carefully scraped off the leaf on which it is growing, thoroughly washed in pure water, and transferred to a drop of water or very dilute glycerine, in which it should be carefully spread out with needles. If air bubbles interfere with the examination, they may be driven off with alcohol, and then the cover glass put on. If the specimen is mounted in glycerine, it will keep indefinitely, if care is taken to seal it up. The plant consists of much-interlaced filaments, divided at intervals by cross-walls.[6] They are nearly colorless, and the contents are not conspicuous. These filaments send up vertical branches (Fig. 39, A), that become divided into a series of short cells by means of cross-walls. The cells thus formed are at first cylindrical, but later bulge out at the sides, becoming broadly oval, and finally become detached as spores (conidia). It is these spores that give the frosty appearance to the early stages of the fungus when seen with the naked eye. The spores fall off very easily when ripe, and germinate quickly in water, sending out two or more tubes that grow into filaments like those of the parent plant (Fig. 39, B).

[6] The filaments are attached to the surface of the leaf by suckers, which are not so readily seen in this species as in some others. A mildew growing abundantly in autumn on the garden chrysanthemum, however, shows them very satisfactorily if a bit of the epidermis of a leaf on which the fungus is just beginning to grow is sliced off with a sharp razor and mounted in dilute glycerine, or water, removing the air with alcohol. These suckers are then seen to be globular bodies, penetrating the outer wall of the cell (Fig. 40).



The spore fruits, as already observed, are formed toward the end of the season, and, in the species under consideration at least, appear to be the result of a sexual process. The sexual organs (if they are really such) are extremely simple, and, owing to their very small size, are not easily found. They arise as short branches at a point where two filaments cross; one of them (Fig. 39, C, ar.), the female cell, or "archicarp," is somewhat larger than the other and nearly oval in form, and soon becomes separated by a partition from the filament that bears it. The other branch (antheridium) grows up in close contact with the archicarp, and like it is shut off by a partition from its filament. It is more slender than the archicarp, but otherwise differs little from it. No actual communication can be shown to be present between the two cells, and it is therefore still doubtful whether fertilization really takes place. Shortly after these organs are full-grown, several short branches grow up about them, and soon completely envelop them (D, E). These branches soon grow together, and cross-walls are formed in them, so that the young spore fruit appears surrounded by a single layer of cells, sufficiently transparent, however, to allow a view of the interior.

The antheridium undergoes no further change, but the archicarp soon divides into two cells,—a small basal one and a larger upper cell. There next grow from the inner surface of the covering cells, short filaments, that almost completely fill the space between the archicarp and the wall. An optical section of such a stage (Fig. 39, F) shows a double wall and the two cells of the archicarp. The spore fruit now enlarges rapidly, and the outer cells become first yellow and then dark brown, the walls becoming thicker and harder as they change color. Sometimes special filaments or appendages grow out from their outer surfaces, and these are also dark-colored. Shortly before the fruit is ripe, the upper cell of the archicarp, which has increased many times in size, shows a division of its contents into eight parts, each of which develops a wall and becomes an oval spore. By crushing the ripe spore fruit, these spores still enclosed in the mother cell (ascus) may be forced out (Fig. 39, H). These spores do not germinate at once, but remain dormant until the next year.



Frequently other structures, resembling somewhat the spore fruits, are found associated with them (Fig. 39, I, K), and were for a long time supposed to be a special form of reproductive organ; but they are now known to belong to another fungus (Cicinnobulus), parasitic upon the mildew. They usually appear at the base of the chains of conidia, causing the basal cell to enlarge to many times its original size, and finally kill the young conidia, which shrivel up. A careful examination reveals the presence of very fine filaments within those of the mildew, which may be traced up to the base of the conidial branch, where the receptacle of the parasite is forming. The spores contained in these receptacles are very small (Fig. 39, K), and when ripe exude in long, worm-shaped masses, if the receptacle is placed in water.

The mildews may be divided into two genera: Podosphaera, with a single ascus in the spore fruit; and Erysiphe, with two or more. In the latter the archicarp branches, each branch bearing a spore sac (Fig. 41, B).

The appendages growing out from the wall of the spore fruit are often very beautiful in form, and the two genera given above are often subdivided according to the form of these appendages.

A common mould closely allied to the mildews is found on various articles of food when allowed to remain damp, and is also very common on botanical specimens that have been poorly dried, and hence is often called "herbarium mould" (Eurotium herbariorum).



The conidia are of a greenish color, and produced on the ends of upright branches which are enlarged at the end, and from which grow out little prominences, which give rise to the conidia in the same way as we have seen in the mildews (Fig. 42, A).

Spore fruits much like those of the mildews are formed later, and are visible to the naked eye as little yellow grains (Fig. 42, D). These contain numerous very small spore sacs (E), each with eight spores.

There are numerous common species of Eurotium, differing in color and size, some being yellow or black, and larger than the ordinary green form.

Another form, common everywhere on mouldy food of all kinds, as well as in other situations, is the blue mould (Penicillium). This, in general appearance, resembles almost exactly the herbarium mould, but is immediately distinguishable by a microscopic examination (Fig. 42, G).

In studying all of these forms, they may be mounted, as directed for the black moulds, in dilute glycerine; but must be handled with great care, as the spores become shaken off with the slightest jar.

Of the larger Ascomycetes, the cup fungi (Discomycetes) may be taken as types. The spore fruit in these forms is often of considerable size, and, as their name indicates, is open, having the form of a flat disc or cup. A brief description of a common one will suffice to give an idea of their structure and development.

Ascobolus (Fig. 43) is a small, disc-shaped fungus, growing on horse dung. By keeping some of this covered with a bell jar for a week or two, so as to retain the moisture, at the end of this time a large crop of the fungus will probably have made its appearance. The part visible is the spore fruit (Fig. 43, A), of a light brownish color, and about as big as a pin-head.

Its development may be readily followed by teasing out in water the youngest specimens that can be found, taking care to take up a little of the substratum with it, as the earliest stages are too small to be visible to the naked eye. The spore fruits arise from filaments not unlike those of the mildews, and are preceded by the formation of an archicarp composed of several cells, and readily seen through the walls of the young fruit (Fig. 43, B). In the study of the early stages, a potash solution will be found useful in rendering them transparent.

The young fruit has much the same structure as that of the mildews, but the spore sacs are much more numerous, and there are special sterile filaments developed between them. If the young spore fruit is treated with chlor-iodide of zinc, it is rendered quite transparent, and the young spore sacs colored a beautiful blue, so that they are readily distinguishable.



The development of the spore sacs may be traced by carefully crushing the young spore fruits in water. The young spore sacs (Fig. 43, E i) are colorless, with granular protoplasm, in which a nucleus can often be easily seen. The nucleus subsequently divides repeatedly, until there are eight nuclei, about which the protoplasm collects to form as many oval masses, each of which develops a wall and becomes a spore (Figs. ii-iv). These are imbedded in protoplasm, which is at first granular, but afterwards becomes almost transparent. As the spores ripen, the wall acquires a beautiful violet-purple color, changing later to a dark purple-brown, and marked with irregular longitudinal ridges (Fig. 43, F). The full-grown spore sacs (Fig. 43, E, W) are oblong in shape, and attached by a short stalk. The sterile filaments between them often become curiously enlarged at the end (G). As the spore fruit ripens, it opens at the top, and spreads out so as to expose the spore sacs as they discharge their contents (Fig. 43, D).

Of the larger cup fungi, those belonging to the genus Peziza (Fig. 43, H) are common, growing on bits of rotten wood on the ground in woods. They are sometimes bright scarlet or orange-red, and very showy. Another curious form is the morel (Morchella), common in the spring in dry woods. It is stalked like a mushroom, but the surface of the conical cap is honeycombed with shallow depressions, lined with the spore sacs.

ORDER Lichenes.

Under the name of lichens are comprised a large number of fungi, differing a good deal in structure, but most of them not unlike the cup fungi. They are, with few exceptions, parasitic upon various forms of algae, with which they are so intimately associated as to form apparently a single plant. They grow everywhere on exposed rocks, on the ground, trunks of trees, fences, etc., and are found pretty much the world over. Among the commonest of plants are the lichens of the genus Parmelia (Fig. 44, A), growing everywhere on tree trunks, wooden fences, etc., forming gray, flattened expansions, with much indented and curled margins. When dry, the plant is quite brittle, but on moistening becomes flexible, and at the same time more or less decidedly green in color. The lower surface is white or brown, and often develops root-like processes by which it is fastened to the substratum. Sometimes small fragments of the plant become detached in such numbers as to form a grayish powder over certain portions of it. These, when supplied with sufficient moisture, will quickly produce new individuals.

Not infrequently the spore fruits are to be met with flat discs of a reddish brown color, two or three millimetres in diameter, and closely resembling a small cup fungus. They are at first almost closed, but expand as they mature (Fig. 44, A, ap.).



If a thin vertical section of the plant is made and sufficiently magnified, it is found to be made up of somewhat irregular, thick-walled, colorless filaments, divided by cross-walls as in the other sac-fungi. In the central parts of the plant these are rather loose, but toward the outside become very closely interwoven and often grown together, so as to form a tough rind. Among the filaments of the outer portion are numerous small green cells, that closer examination shows to be individuals of Protococcus, or some similar green algae, upon which the lichen is parasitic. These are sufficiently abundant to form a green line just inside the rind if the section is examined with a simple lens (Fig. 44, B).

The spore fruits of the lichens resemble in all essential respects those of the cup fungi, and the spore sacs (Fig. 44, F) are much the same, usually, though not always, containing eight spores, which are sometimes two-celled. The sterile filaments between the spore sacs usually have thickened ends, which are dark-colored, and give the color to the inner surface of the spore fruit.

In Figure 45, H, is shown one of the so-called "Soredia,"[7] a group of the algae, upon which the lichen is parasitic, surrounded by some of the filaments, the whole separating spontaneously from the plant and giving rise to a new one.

[7] Sing. soredium.

Owing to the toughness of the filaments, the finer structure of the lichens is often difficult to study, and free use of caustic potash is necessary to soften and make them manageable.



According to their form, lichens are sometimes divided into the bushy (fruticose), leafy (frondose), incrusting (crustaceous), and gelatinous. Of the first, the long gray Usnea (Fig. 45, A, B), which drapes the branches of trees in swamps, is a familiar example; of the second, Parmelia, Sticta (Fig. 45, C) and Peltigera (D) are types; of the third, Graphis (G), common on the trunks of beech-trees, to which it closely adheres; and of the last, Collema (Fig. 44, C, D, E), a dark greenish, gelatinous form, growing on mossy tree trunks, and looking like a colony of Nostoc, which indeed it is, but differing from an ordinary colony in being penetrated everywhere by the filaments of the fungus growing upon it.

Not infrequently in this form, as well as in other lichens, special cavities, known as spermogonia (Fig. 44, D), are found, in which excessively small spores are produced, which have been claimed to be male reproductive cells, but the latest investigations do not support this theory.



The last group of the Ascomycetes are the "black fungi," Pyrenomycetes, represented by the black knot of cherry and plum trees, shown in Figure 46. They are mainly distinguished from the cup fungi by producing their spore sacs in closed cavities. Some are parasites; others live on dead wood, leaves, etc., forming very hard masses, generally black in color, giving them their common name. Owing to the hardness of the masses, they are very difficult to manipulate; and, as the structure is not essentially different from that of the Discomycetes, the details will not be entered into here.

Of the parasitic forms, one of the best known is the "ergot" of rye, more or less used in medicine. Other forms are known that attack insects, particularly caterpillars, which are killed by their attacks.



CHAPTER X.

FUNGI—Continued.

CLASS Basidiomycetes.

The Basidiomycetes include the largest and most highly developed of the fungi, among which are many familiar forms, such as the mushrooms, toadstools, puff-balls, etc. Besides these large and familiar forms, there are other simpler and smaller ones that, according to the latest investigations, are probably related to them, though formerly regarded as constituting a distinct group. The most generally known of these lower Basidiomycetes are the so-called rusts. The larger Basidiomycetes are for the most part saprophytes, living in decaying vegetable matter, but a few are true parasites upon trees and others of the flowering plants.

All of the group are characterized by the production of spores at the top of special cells known as basidia,[8] the number produced upon a single basidium varying from a single one to several.

[8] Sing. basidium.

Of the lower Basidiomycetes, the rusts (Uredineae) offer common and easily procurable forms for study. They are exclusively parasitic in their habits, growing within the tissues of the higher land plants, which they often injure seriously. They receive their popular name from the reddish color of the masses of spores that, when ripe, burst through the epidermis of the host plant. Like many other fungi, the rusts have several kinds of spores, which are often produced on different hosts; thus one kind of wheat rust lives during part of its life within the leaves of the barberry, where it produces spores quite different from those upon the wheat; the cedar rust, in the same way, is found at one time attacking the leaves of the wild crab-apple and thorn.

[Illustration: FIG. 47.—A, a branch of red cedar attacked by a rust (Gymnosporangium), causing a so-called "cedar apple," x 1/2. B, spores of the same, one beginning to germinate, x 300. C, a spore that has germinated, each cell producing a short, divided filament (basidium), which in turn gives rise to secondary spores (sp.), x 300. D, part of the leaf of a hawthorn attacked by the cluster cup stage of the same fungus, upper side showing spermogonia, natural size. E, cluster cups (Roestelia) of the same fungus, natural size. F, tip of a leaf of the Indian turnip (Arisaema), bearing the cluster cup (AEcidium) stage of a rust, x 2. G, vertical section through a young cluster cup. H, similar section through a mature one, x 50. I, germinating spores of H, x 300. J, part of a corn leaf, with black rust, natural size. K, red rust spore of the wheat rust (Puccinia graminis), x 300. L, forms of black-rust spores: i, Uromyces; ii, Puccinia; iii, Phragmidium.]

The first form met with in most rusts is sometimes called the "cluster-cup" stage, and in many species is the only stage known. In Figure 47, F, is shown a bit of the leaf of the Indian turnip (Arisaema) affected by one of these "cluster-cup" forms. To the naked eye, or when slightly magnified, the masses of spores appear as bright orange spots, mostly upon the lower surface. The affected leaves are more or less checked in their growth, and the upper surface shows lighter blotches, corresponding to the areas below that bear the cluster cups. These at first appear as little elevations of a yellowish color, and covered with the epidermis; but as the spores ripen they break through the epidermis, which is turned back around the opening, the whole forming a little cup filled with a bright orange red powder, composed of the loose masses of spores.

Putting a piece of the affected leaf between two pieces of pith so as to hold it firmly, with a little care thin vertical sections of the leaf, including one of the cups, may be made, and mounted, either in water or glycerine, removing the air with alcohol. We find that the leaf is thickened at this point owing to a diseased growth of the cells of the leaf, induced by the action of the fungus. The mass of spores (Fig. 47, G) is surrounded by a closely woven mass of filaments, forming a nearly globular cavity. Occupying the bottom of the cup are closely set, upright filaments, each bearing a row of spores, arranged like those of the white rusts, but so closely crowded as to be flattened at the sides. The outer rows have thickened walls, and are grown together so as to form the wall of the cup.

The spores are filled with granular protoplasm, in which are numerous drops of orange-yellow oil, to which is principally due their color. As the spores grow, they finally break the overlying epidermis, and then become rounded as the pressure from the sides is relieved. They germinate within a few hours if placed in water, sending out a tube, into which pass the contents of the spore (Fig. 47, I).

One of the most noticeable of the rusts is the cedar rust (Gymnosporangium), forming the growths known as "cedar apples," often met with on the red cedar. These are rounded masses, sometimes as large as a walnut, growing upon the small twigs of the cedar (Fig. 47, A). This is a morbid growth of the same nature as those produced by the white rusts and smuts. If one of these cedar apples is examined in the late autumn or winter, it will be found to have the surface dotted with little elevations covered by the epidermis, and on removing this we find masses of forming spores. These rupture the epidermis early in the spring, and appear then as little spikes of a rusty red color. If they are kept wet for a few hours, they enlarge rapidly by the absorption of water, and may reach a length of four or five centimetres, becoming gelatinous in consistence, and sometimes almost entirely hiding the surface of the "apple." In this stage the fungus is extremely conspicuous, and may frequently be met with after rainy weather in the spring.

This orange jelly, as shown by the microscope, is made up of elongated two-celled spores (teleuto spores), attached to long gelatinous stalks (Fig. 47, B). They are thick-walled, and the contents resemble those of the cluster-cup spores described above.

To study the earlier stages of germination it is best to choose specimens in which the masses of spores have not been moistened. By thoroughly wetting these, and keeping moist, the process of germination may be readily followed. Many usually begin to grow within twenty-four hours or less. Each cell of the spore sends out a tube (Fig. 47, C), through an opening in the outer wall, and this tube rapidly elongates, the spore contents passing into it, until a short filament (basidium) is formed, which then divides into several short cells. Each cell develops next a short, pointed process, which swells up at the end, gradually taking up all the contents of the cell, until a large oval spore (sp.) is formed at the tip, containing all the protoplasm of the cell.

Experiments have been made showing that these spores do not germinate upon the cedar, but upon the hawthorn or crab-apple, where they produce the cluster-cup stage often met with late in the summer. The affected leaves show bright orange-yellow spots about a centimetre in diameter (Fig. 47, D), and considerably thicker than the other parts of the leaf. On the upper side of these spots may be seen little black specks, which microscopic examination shows to be spermogonia, resembling those of the lichens. Later, on the lower surface, appear the cluster cups, whose walls are prolonged so that they form little tubular processes of considerable length (Fig. 47, E).

In most rusts the teleuto spores are produced late in the summer or autumn, and remain until the following spring before they germinate. They are very thick-walled, the walls being dark-colored, so that in mass they appear black, and constitute the "black-rust" stage (Fig. 47, J). Associated with these, but formed earlier, and germinating immediately, are often to be found large single-celled spores, borne on long stalks. They are usually oval in form, rather thin-walled, but the outer surface sometimes provided with little points. The contents are reddish, so that in mass they appear of the color of iron rust, and cause the "red rust" of wheat and other plants, upon which they are growing.

The classification of the rusts is based mainly upon the size and shape of the teleuto spores where they are known, as the cluster-cup and red-rust stages are pretty much the same in all. Of the commoner genera Melampsora, and Uromyces (Fig. 47, L i), have unicellular teleuto spores; Puccinia (ii) and Gymnosporangium, two-celled spores; Triphragmium, three-celled; and Phragmidium (iii), four or more.

The rusts are so abundant that a little search can scarcely fail to find some or all of the stages. The cluster-cup stages are best examined fresh, or from alcoholic material; the teleuto spores may be dried without affecting them.

Probably the best-known member of the group is the wheat rust (Puccinia graminis), which causes so much damage to wheat and sometimes to other grains. The red-rust stage may be found in early summer; the black-rust spores in the stubble and dead leaves in the autumn or spring, forming black lines rupturing the epidermis.

Probably to be associated with the lower Basidiomycetes are the large fungi of which Tremella (Fig. 51, A) is an example. They are jelly-like forms, horny and somewhat brittle when dry, but becoming soft when moistened. They are common, growing on dead twigs, logs, etc., and are usually brown or orange-yellow in color.

Of the higher Basidiomycetes, the toadstools, mushrooms, etc., are the highest, and any common form will serve for study. One of the most accessible and easily studied forms is Coprinus, of which there are several species growing on the excrement of various herbivorous animals. They not infrequently appear on horse manure that has been kept covered with a glass for some time, as described for Ascobolus. After two or three weeks some of these fungi are very likely to make their appearance, and new ones continue to develop for a long time.



The first trace of the plant, visible to the naked eye, is a little downy, white speck, just large enough to be seen. This rapidly increases in size, becoming oblong in shape, and growing finally somewhat darker in color; and by the time it reaches a height of a few millimetres a short stalk becomes perceptible, and presently the whole assumes the form of a closed umbrella. The top is covered with little prominences, that diminish in number and size toward the bottom. After the cap reaches its full size, the stalk begins to grow, slowly at first, but finally with great rapidity, reaching a height of several centimetres within a few hours. At the same time that the stalk is elongating, the cap spreads out, radial clefts appearing on its upper surface, which flatten out very much as the folds of an umbrella are stretched as it opens, and the spaces between the clefts appear as ridges, comparable to the ribs of the umbrella (Fig. 48, B). The under side of the cap has a number of ridges running from the centre to the margin, and of a black color, due to the innumerable spores covering their surface (C). Almost as soon as the umbrella opens, the spores are shed, and the whole structure shrivels up and dissolves, leaving almost no trace behind.

If we examine microscopically the youngest specimens procurable, freeing from air with alcohol, and mounting in water or dilute glycerine, we find it to be a little, nearly globular mass of colorless filaments, with numerous cross-walls, the whole arising from similar looser filaments imbedded in the substratum (Fig. 48, G). If the specimen is not too young, a denser central portion can be made out, and in still older ones (Fig. 48, H) this central mass has assumed the form of a short, thick stalk, crowned by a flat cap, the whole invested by a loose mass of filaments that merge more or less gradually into the central portion. By the time the spore fruit (for this structure corresponds to the spore fruit of the Ascomycetes) reaches a height of two or three millimetres, and is plainly visible to the naked eye, the cap grows downward at the margins, so as to almost entirely conceal the stalk. A longitudinal section of such a stage shows the stalk to be composed of a small-celled, close tissue becoming looser in the cap, on whose inner surface the spore-bearing ridges ("gills" or Lamellae) have begun to develop. Some of these run completely to the edge of the cap, others only part way. To study their structure, make cross-sections of the cap of a nearly full-grown, but unopened, specimen, and this will give numerous sections of the young gills. We find them to be flat plates, composed within of loosely interwoven filaments, whose ends stand out at right angles to the surface of the gills, forming a layer of closely-set upright cells (basidia) (Fig. 48, D). These are at first all alike, but later some of them become club-shaped, and develop at the end several (usually four) little points, at the end of which spores are formed in exactly the same way as we saw in the germinating teleuto spores of the cedar rust, all the protoplasm of the basidium passing into the growing spores (Fig. 48, E, F). The ripe spores (E, sp.) are oval, and possess a firm, dark outer wall. Occasionally some of the basidia develop into very large sterile cells (E, x), projecting far beyond the others, and often reaching the neighboring gill.

Similar in structure and development to Coprinus are all the large and common forms; but they differ much in the position of the spore-bearing tissue, as well as in the form and size of the whole spore fruit. They are sometimes divided, according to the position of the spores, into three orders: the closed-fruited (Angiocarpous) forms, the half-closed (Hemi-angiocarpous), and the open or naked-fruited forms (Gymnocarpous).



Of the first, the puff-balls (Fig. 49) are common examples. One species, the giant puff-ball (Lycoperdon giganteum), often reaches a diameter of thirty to forty centimetres. The earth stars (Geaster) have a double covering to the spore fruit, the outer one splitting at maturity into strips (Fig. 49, B). Another pretty and common form is the little birds'-nest fungus (Cyathus), growing on rotten wood or soil containing much decaying vegetable matter (Fig. 50).



In the second order the spores are at first protected, as we have seen in Coprinus, which belongs to this order, but finally become exposed. Here belong the toadstools and mushrooms (Fig. 51, B), the large shelf-shaped fungi (Polyporus), so common on tree trunks and rotten logs (Fig. 51, C, D, E), and the prickly fungus (Hydnum) (Fig. 51, G).



Of the last, or naked-fruited forms, the commonest belong to the genus Clavaria (Fig. 51, F), smooth-branching forms, usually of a brownish color, bearing the spores directly upon the surface of the branches.



CHAPTER XI.

SUB-KINGDOM IV.

BRYOPHYTA.

The Bryophytes, or mosses, are for the most part land plants, though a few are aquatic, and with very few exceptions are richly supplied with chlorophyll. They are for the most part small plants, few of them being over a few centimetres in height; but, nevertheless, compared with the plants that we have heretofore studied, quite complex in their structure. The lowest members of the group are flattened, creeping plants, or a few of them floating aquatics, without distinct stem and leaves; but the higher ones have a pretty well-developed central axis or stem, with simple leaves attached.

There are two classes—I. Liverworts (Hepaticae), and II. Mosses (Musci).

CLASS I.—THE LIVERWORTS.

One of the commonest of this class, and to be had at any time, is named Madotheca. It is one of the highest of the class, having distinct stem and leaves. It grows most commonly on the shady side of tree trunks, being most luxuriant near the ground, where the supply of moisture is most constant. It also occurs on stones and rocks in moist places. It closely resembles a true moss in general appearance, and from the scale-like arrangement of its leaves is sometimes called "scale moss."

The leaves (Fig. 52, A, B) are rounded in outline unequally, two-lobed, and arranged in two rows on the upper side of the stem, so closely overlapping as to conceal it entirely. On the under side are similar but smaller leaves, less regularly disposed. The stems branch at intervals, the branches spreading out laterally so that the whole plant is decidedly flattened. On the under side are fine, whitish hairs, that fasten it to the substratum. If we examine a number of specimens, especially early in the spring, a difference will be observed in the plants. Some of them will be found to bear peculiar structures (Fig. 52, C, D), in which the spores are produced. These are called "sporogonia." They are at first globular, but when ripe open by means of four valves, and discharge a greenish brown mass of spores. An examination of the younger parts of the same plants will probably show small buds (Fig. 54, H), which contain the female reproductive organs, from which the sporogonia arise.



On other plants may be found numerous short side branches (Fig. 53, B), with very closely set leaves. If these are carefully separated, the antheridia can just be seen as minute whitish globules, barely visible to the naked eye. Plants that, like this one, have the male and female reproductive organs on distinct plants, are said to be "dioecious."

A microscopical examination of the stem and leaves shows their structure to be very simple. The former is cylindrical, and composed of nearly uniform elongated cells, with straight cross-walls. The leaves consist of a single layer of small, roundish cells, which, like those of the stem, contain numerous rounded chloroplasts, to which is due their dark green color.

The tissues are developed from a single apical cell, but it is difficult to obtain good sections through it.

The antheridia are borne singly at the bases of the leaves on the special branches already described (Fig. 53, A, an.). By carefully dissecting with needles such a branch in a drop of water, some of the antheridia will usually be detached uninjured, and may be readily studied, the full-grown ones being just large enough to be seen with the naked eye. They are globular bodies, attached by a stalk composed of two rows of cells. The globular portion consists of a wall of chlorophyll-bearing cells, composed of two layers below, but single above (Fig. 53, C). Within is a mass of excessively small cells, each of which contains a spermatozoid. In the young antheridium (A, an.) the wall is single throughout, and the central cells few in number. To study them in their natural position, thin longitudinal sections of the antheridial branch should be made.



When ripe, if brought into water, the antheridium bursts at the top into a number of irregular lobes that curl back and allow the mass of sperm cells to escape. The spermatozoids, which are derived principally from the nucleus of the sperm cells (53, D) are so small as to make a satisfactory examination possible only with very powerful lenses. The ripe spermatozoid is coiled in a flat spiral (53, E), and has two excessively delicate cilia, visible only under the most favorable circumstances.

The female organ in the bryophytes is called an "archegonium," and differs considerably from anything we have yet studied, but recalls somewhat the structure of the ooegonium of Chara. They are found in groups, contained in little bud-like branches (54, H). In order to study them, a plant should be chosen that has numbers of such buds, and the smallest that can be found should be used. Those containing the young archegonia are very small; but after one has been fertilized, the leaves enclosing it grow much larger, and the bud becomes quite conspicuous, being surrounded by two or three comparatively large leaves. By dissecting the young buds, archegonia in all stages of growth may be found.



When very young the archegonium is composed of an axial row of three cells, surrounded by a single outer layer of cells, the upper ones forming five or six regular rows, which are somewhat twisted (Fig. 54, A, B). As it becomes older, the lower part enlarges slightly, the whole looking something like a long-necked flask (C, D). The centre of the neck is occupied by a single row of cells (canal cells), with more granular contents than the outer cells, the lowest cell of the row being somewhat larger than the others (Fig. 54, C, o). When nearly ripe, the division walls of the canal cells are absorbed, and the protoplasm of the lowest cell contracts and forms a globular naked cell, the egg cell (D, o). If a ripe archegonium is placed in water, it soon opens at the top, and the contents of the canal cells are forced out, leaving a clear channel down to the egg cell. If the latter is not fertilized, the inner walls of the neck cells turn brown, and the egg cell dies; but if a spermatozoid penetrates to the egg cell, the latter develops a wall and begins to grow, forming the embryo or young sporogonium.



The first division wall to be formed in the embryo is transverse, and is followed by vertical ones (Fig. 54, E, em.). As the embryo enlarges, the walls of the basal part of the archegonium grow rapidly, so that the embryo remains enclosed in the archegonium until it is nearly full-grown (Fig. 55). As it increases in size, it becomes differentiated into three parts: a wedge-shaped base or "foot" penetrating downward into the upper part of the plant, and serving to supply the embryo with nourishment; second, a stalk supporting the third part, the capsule or spore-bearing portion of the fruit. The capsule is further differentiated into a wall, which later becomes dark colored, and a central cavity, in which are developed special cells, some of which by further division into four parts produce the spores, while the others, elongating enormously, give rise to special cells, called elaters (Fig. 56, B).



The ripe spores are nearly globular, contain chlorophyll and drops of oil, and the outer wall is brown and covered with fine points (Fig. 56, A). The elaters are long-pointed cells, having on the inner surface of the wall a single or double dark brown spiral band. These bands are susceptible to changes in moisture, and by their movements probably assist in scattering the spores after the sporogonium opens.

Just before the spores are ripe, the stalk of the sporogonium elongates rapidly, carrying up the capsule, which breaks through the archegonium wall, and finally splits into four valves, and discharges the spores.

There are four orders of the liverworts represented in the United States, three of which differ from the one we have studied in being flattened plants, without distinct stems and leaves,—at least, the leaves when present are reduced to little scales upon the lower surface.

The first order (Ricciaceae) are small aquatic forms, or grow on damp ground or rotten logs. They are not common forms, and not likely to be encountered by the student. One of the floating species is shown in figure 57, A.

The second order, the horned liverworts (Anthoceroteae), are sometimes to be met with in late summer and autumn, forms growing mostly on damp ground, and at once recognizable by their long-pointed sporogonia, which open when ripe by two valves, like a bean pod (Fig. 57, B).

The third order (Marchantiaceae) includes the most conspicuous members of the whole class. Some of them, like the common liverwort (Marchantia), shown in Figure 57, F, K, and the giant liverwort (Fig. 57, D), are large and common forms, growing on the ground in shady places, the former being often found also in greenhouses. They are fastened to the ground by numerous fine, silky hairs, and the tissues are well differentiated, the upper surface of the plant having a well-marked epidermis, with peculiar breathing pores, large enough to be seen with the naked eye (Fig. 57, E, J, K) Each of these is situated in the centre of a little area (Fig. 57, E), and beneath it is a large air space, into which the chlorophyll-bearing cells (cl.) of the plant project (J).

The sexual organs are often produced in these forms upon special branches (G), or the antheridia may be sunk in discs on the upper side of the stem (D, an.).

[Illustration: FIG. 57.—Forms of liverworts. A, Riccia, natural size. B, Anthoceros (horned liverwort), natural size. sp. sporogonia. C, Lunularia, natural size, x, buds. D, giant liverwort (Conocephalus), natural size. an. antheridial disc. E, small piece of the epidermis, showing the breathing pores, x 2. F, common liverwort (Marchantia), x 2. x, cups containing buds. G, archegonial branch of common liverwort, natural size. H, two young buds from the common liverwort, x 150. I, a full-grown bud, x 25. J, vertical section through the body of Marchantia, cutting through a breathing pore (s), x 50. K, surface view of a breathing pore, x 150. L, a leafy liverwort (Jungermannia). sp. sporogonium, x 2.]

Some forms, like Marchantia and Lunularia (Fig. 57, C), produce little cups (x), circular in the first, semicircular in the second, in which special buds (H, I) are formed that fall off and produce new plants.

The highest of the liverworts (Jungermanniaceae) are, for the most part, leafy forms like Madotheca, and represented by a great many common forms, growing usually on tree trunks, etc. They are much like Madotheca in general appearance, but usually very small and inconspicuous, so as to be easily overlooked, especially as their color is apt to be brownish, and not unlike that of the bark on which they grow (Fig. 57, L).

CLASS II.—THE TRUE MOSSES.

The true mosses (Musci) resemble in many respects the higher liverworts, such as Madotheca or Jungermannia, all of them having well-marked stems and leaves. The spore fruit is more highly developed than in the liverworts, but never contains elaters.

A good idea of the general structure of the higher mosses may be had from a study of almost any common species. One of the most convenient, as well as common, forms (Funaria) is to be had almost the year round, and fruits at almost all seasons, except midwinter. It grows in close patches on the ground in fields, at the bases of walls, sometimes in the crevices between the bricks of sidewalks, etc. If fruiting, it may be recognized by the nodding capsule on a long stalk, that is often more or less twisted, being sensitive to changes in the moisture of the atmosphere. The plant (Fig. 58, A, B) has a short stem, thickly set with relatively large leaves. These are oblong and pointed, and the centre is traversed by a delicate midrib. The base of the stem is attached to the ground by numerous fine brown hairs.

The mature capsule is broadly oval in form (Fig. 58, C), and provided with a lid that falls off when the spores are ripe. While the capsule is young it is covered by a pointed membranous cap (B, cal.) that finally falls off. When the lid is removed, a fine fringe is seen surrounding the opening of the capsule, and serving the same purpose as the elaters of the liverworts (Fig. 58, E).



If the lower part of the stem is carefully examined with a lens, we may detect a number of fine green filaments growing from it, looking like the root hairs, except for their color. Sometimes the ground about young patches of the moss is quite covered by a fine film of such threads, and looking carefully over it probably very small moss plants may be seen growing up here and there from it.



This moss is dioecious. The male plants are smaller than the female, and may be recognized by the bright red antheridia which are formed at the end of the stem in considerable numbers, and surrounded by a circle of leaves so that the whole looks something like a flower. (This is still more evident in some other mosses. See Figure 65, E, F.)

The leaves when magnified are seen to be composed of a single layer of cells, except the midrib, which is made up of several thicknesses of elongated cells. Where the leaf is one cell thick, the cells are oblong in form, becoming narrower as they approach the midrib and the margin. They contain numerous chloroplasts imbedded in the layer of protoplasm that lines the wall. The nucleus (Fig. 63, C, n) may usually be seen without difficulty, especially if the leaf is treated with iodine. This plant is one of the best for studying the division of the chloroplasts, which may usually be found in all stages of division (Fig. 63, D). In the chloroplasts, especially if the plant has been exposed to light for several hours, will be found numerous small granules, that assume a bluish tint on the application of iodine, showing them to be starch grains. If the plant is kept in the dark for a day or two, these will be absent, having been used up; but if exposed to the light again, new ones will be formed, showing that they are formed only under the action of light.



Starch is composed of carbon, hydrogen, and oxygen, and so far as is known is only produced by chlorophyll-bearing cells, under the influence of light. The carbon used in the manufacture of starch is taken from the atmosphere in the form of carbonic acid, so that green plants serve to purify the atmosphere by the removal of this substance, which is deleterious to animal life, while at the same time the carbon, an essential part of all living matter, is combined in such form as to make it available for the food of other organisms.

The marginal cells of the leaf are narrow, and some of them prolonged into teeth.

A cross-section of the stem (63, E) shows on the outside a single row of epidermal cells, then larger chlorophyll-bearing cells, and in the centre a group of very delicate, small, colorless cells, which in longitudinal section are seen to be elongated, and similar to those forming the midrib of the leaf. These cells probably serve for conducting fluids, much as the similar but more perfectly developed bundles of cells (fibro-vascular bundles) found in the stems and leaves of the higher plants.

The root hairs, fastening the plant to the ground, are rows of cells with brown walls and oblique partitions. They often merge insensibly into the green filaments (protonema) already noticed. These latter have usually colorless walls, and more numerous chloroplasts, looking very much like a delicate specimen of Cladophora or some similar alga. If a sufficient number of these filaments is examined, some of them will probably show young moss plants growing from them (Fig. 63, A, k), and with a little patience the leafy plant can be traced back to a little bud originating as a branch of the filament. Its diameter is at first scarcely greater than that of the filament, but a series of walls, close together, are formed, so placed as to cut off a pyramidal cell at the top, forming the apical cell of the young moss plant. This apical cell has the form of a three-sided pyramid with the base upward. From it are developed three series of cells, cut off in succession from the three sides, and from these cells are derived all the tissues of the plant which soon becomes of sufficient size to be easily recognizable.

The protonemal filaments may be made to grow from almost any part of the plant by keeping it moist, but grow most abundantly from the base of the stem.

The sexual organs are much like those of the liverworts and are borne at the apex of the stems.

The antheridia (Figs. 59, 60) are club-shaped bodies with a short stalk. The upper part consists of a single layer of large chlorophyll-bearing cells, enclosing a mass of very small, nearly cubical, colorless, sperm cells each of which contains an excessively small spermatozoid.

The young antheridium has an apical cell giving rise to two series of segments (Fig. 60, A), which in the earlier stages are very plainly marked.

When ripe the chlorophyll in the outer cells changes color, becoming red, and if a few such antheridia from a plant that has been kept rather dry for a day or two, are teased out in a drop of water, they will quickly open at the apex, the whole mass of sperm cells being discharged at once.

Among the antheridia are borne peculiar hairs (Fig. 59, p) tipped by a large globular cell.



Owing to their small size the spermatozoids are difficult to see satisfactorily and other mosses (e.g. peat mosses, Figure 64, the hairy cap moss, Figure 65, I), are preferable where obtainable. The spermatozoids of a peat moss are shown in Figure 60, D. Like all of the bryophytes they have but two cilia.

The archegonia (Fig. 61) should be looked for in the younger plants in the neighborhood of those that bear capsules. Like the antheridia they occur in groups. They closely resemble those of the liverworts, but the neck is longer and twisted and the base more massive. Usually but a single one of the group is fertilized.



To study the first division of the embryo, it is usually necessary to render the archegonium transparent, which may be done by using a little caustic potash; or letting it lie for a few hours in dilute glycerine will sometimes suffice. If potash is used it must be thoroughly washed away, by drawing pure water under the cover glass with a bit of blotting paper, until every trace of the potash is removed. The first wall in the embryo is nearly at right angles to the axis of the archegonium and divides the egg cell into nearly equal parts. This is followed by nearly vertical walls in each cell (Fig. 62, A). Very soon a two-sided apical cell (Fig. 62, B, a) is formed in the upper half of the embryo, which persists until the embryo has reached a considerable size. As in the liverworts the young embryo is completely covered by the growing archegonium wall.

The embryo may be readily removed from the archegonium by adding a little potash to the water in which it is lying, allowing it to remain for a few moments and pressing gently upon the cover glass with a needle. In this way it can be easily forced out of the archegonium, and then by thoroughly washing away the potash, neutralizing if necessary with a little acetic acid, very beautiful preparations may be made. If desired, these may be mounted permanently in glycerine which, however, must be added very gradually to avoid shrinking the cells.



For some time the embryo has a nearly cylindrical form, but as it approaches maturity the differentiation into stalk and capsule becomes apparent. The latter increases rapidly in diameter, assuming gradually the oval shape of the full-grown capsule. A longitudinal section of the nearly ripe capsule (Fig. 58, G) shows two distinct portions; an outer wall of two layers of cells, and an inner mass of cells in some of which the spores are produced. This inner mass of cells is continuous with the upper part of the capsule, but connected with the side walls and bottom by means of slender, branching filaments of chlorophyll-bearing cells.

The spores arise from a single layer of cells near the outside of the inner mass of cells (G, sp.). These cells (H, sp.) are filled with glistening, granular protoplasm; have a large and distinct nucleus, and no chlorophyll. They finally become entirely separated and each one gives rise to four spores which closely resemble those of the liverworts but are smaller.

Near the base of the capsule, on the outside, are formed breathing pores (Fig. 58, F) quite similar to those of the higher plants.

If the spores are kept in water for a few days they will germinate, bursting the outer brown coat, and the contents protruding through the opening surrounded by the colorless inner spore membrane. The protuberance grows rapidly in length and soon becomes separated from the body of the spore by a wall, and lengthening, more and more, gives rise to a green filament like those we found attached to the base of the full-grown plant, and like those giving rise to buds that develop into leafy plants.

CLASSIFICATION OF THE MOSSES.

The mosses may be divided into four orders: I. The peat mosses (Sphagnaceae); II. Andreaeaceae; III. Phascaceae; IV. The common mosses (Bryaceae).



The peat mosses (Fig. 64) are large pale-green mosses, growing often in enormous masses, forming the foundation of peat-bogs. They are of a peculiar spongy texture, very light when dry, and capable of absorbing a great amount of water. They branch (Fig. 64, A), the branches being closely crowded at the top, where the stems continue to grow, dying away below.



The sexual organs are rarely met with, but should be looked for late in autumn or early spring. The antheridial branches are often bright-colored, red or yellow, so as to be very conspicuous. The capsules, which are not often found, are larger than in most of the common mosses, and quite destitute of a stalk, the apparent stalk being a prolongation of the axis of the plant in the top of which the base of the sporogonium is imbedded. The capsule is nearly globular, opening by a lid at the top (Fig. 64, B).

A microscopical examination of the leaves, which are quite destitute of a midrib, shows them to be composed of a network of narrow chlorophyll-bearing cells surrounding much larger empty ones whose walls are marked with transverse thickenings, and perforated here and there with large, round holes (Fig. 64, C). It is to the presence of these empty cells that the plant owes its peculiar spongy texture, the growing plants being fairly saturated with water.

The Andreaeaceae are very small, and not at all common. The capsule splits into four valves, something like a liverwort.

The Phascaceae are small mosses growing on the ground or low down on the trunks of trees, etc. They differ principally from the common mosses in having the capsule open irregularly and not by a lid. The commonest forms belong to the genus Phascum (Fig. 65, A).

The vast majority of the mosses the student is likely to meet with belong to the last order, and agree in the main with the one described. Some of the commoner forms are shown in Figure 65.



CHAPTER XII.

SUB-KINGDOM V.

PTERIDOPHYTES.

If we compare the structure of the sporogonium of a moss or liverwort with the plant bearing the sexual organs, we find that its tissues are better differentiated, and that it is on the whole a more complex structure than the plant that bears it. It, however, remains attached to the parent plant, deriving its nourishment in part through the "foot" by means of which it is attached to the plant.

In the Pteridophytes, however, we find that the sporogonium becomes very much more developed, and finally becomes entirely detached from the sexual plant, developing in most cases roots that fasten it to the ground, after which it may live for many years, and reach a very large size.

The sexual plant, which is here called the "prothallium," is of very simple structure, resembling the lower liverworts usually, and never reaches more than about a centimetre in diameter, and is often much smaller than this.

The common ferns are the types of the sub-kingdom, and a careful study of any of these will illustrate the principal peculiarities of the group. The whole plant, as we know it, is really nothing but the sporogonium, originating from the egg cell in exactly the same way as the moss sporogonium, and like it gives rise to spores which are formed upon the leaves.

The spores may be collected by placing the spore-bearing leaves on sheets of paper and letting them dry, when the ripe spores will be discharged covering the paper as a fine, brown powder. If these are sown on fine, rather closely packed earth, and kept moist and covered with glass so as to prevent evaporation, within a week or two a fine, green, moss-like growth will make its appearance, and by the end of five or six weeks, if the weather is warm, little, flat, heart-shaped plants of a dark-green color may be seen. These look like small liverworts, and are the sexual plants (prothallia) of our ferns (Fig. 66, F). Removing one of these carefully, we find on the lower side numerous fine hairs like those on the lower surface of the liverworts, which fasten it firmly to the ground. By and by, if our culture has been successful, we may find attached to some of the larger of these, little fern plants growing from the under side of the prothallia, and attached to the ground by a delicate root. As the little plant becomes larger the prothallium dies, leaving it attached to the ground as an independent plant, which after a time bears the spores.