Fig. 33.Fig. 33.—A, leaf of pig-weed (Amarantus), with spots of white rust (c), one-half natural size.B, non-sexual spores (conidia).C, the same germinating.D, zoöspores.E, germinating zoöspores.sp.the spore.F, young.G, mature sexual organs. InG, the tube may be seen connecting the antheridium (an.), with the egg cell (o).H, a ripe resting spore still surrounded by the wall of the oögonium.I, a part of a filament of the fungus, showing its irregular form. All × 300.
Fig. 33.—A, leaf of pig-weed (Amarantus), with spots of white rust (c), one-half natural size.B, non-sexual spores (conidia).C, the same germinating.D, zoöspores.E, germinating zoöspores.sp.the spore.F, young.G, mature sexual organs. InG, the tube may be seen connecting the antheridium (an.), with the egg cell (o).H, a ripe resting spore still surrounded by the wall of the oögonium.I, a part of a filament of the fungus, showing its irregular form. All × 300.
Under normal conditions the spores probably germinate when the leaves are wet, and the filaments enter the plant through the breathing pores onthe 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 (oöspores) 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 oögonium, and differs in no essential respect from that ofVaucheria.Frequently a smaller cell (antheridium), arising from a neighboring filament, and in close contact with the oögonium, 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.
Under normal conditions the spores probably germinate when the leaves are wet, and the filaments enter the plant through the breathing pores onthe 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 (oöspores) 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 oögonium, and differs in no essential respect from that ofVaucheria.
Frequently a smaller cell (antheridium), arising from a neighboring filament, and in close contact with the oögonium, 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.
Fig. 34.Fig. 34.—Fragment of a filament of the white rust of the shepherd’s-purse, showing the suckers (h), × 300.
Fig. 34.—Fragment of a filament of the white rust of the shepherd’s-purse, showing the suckers (h), × 300.
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.
Fig. 35.Fig. 35.—Non-sexual spores of the vine mildew (Peronospora viticola), × 150.
Fig. 35.—Non-sexual spores of the vine mildew (Peronospora viticola), × 150.
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).
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).
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.
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). Somewhatlater, if carefully examined with a lens, little round, white bodies may be seen scattered among the filaments.
Fig. 36.Fig. 36.—A, an insect that has decayed in water, and become attacked by a water mould (Saprolegnia), natural size.B, a ripe zoösporangium, × 100.C, the same discharging the spores.D, active.E, germinating zoöspores, × 300.F, a second sporangium forming below the empty one.Gi–iv, development of the oögonium, × 100.H, ripe oögonium filled with resting spores, × 100.
Fig. 36.—A, an insect that has decayed in water, and become attacked by a water mould (Saprolegnia), natural size.B, a ripe zoösporangium, × 100.C, the same discharging the spores.D, active.E, germinating zoöspores, × 300.F, a second sporangium forming below the empty one.Gi–iv, development of the oögonium, × 100.H, ripe oögonium filled with resting spores, × 100.
On carefully removing a bit of the younger growth and examining it microscopically, it is found to consist of long filaments much like those ofVaucheria, 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 zoöspores, produced in great numbers in sporangia at the ends of the branches. The protoplasm collects here much as we saw inV. 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 appearancein 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 zoöspores 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 zoöspore, like those already described. By killing the zoöspores 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 zoöspores there are also resting spores developed. Oögonia like those ofVaucheriaor thePeronosporeæare formed usually after the formation of zoöspores 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]The oögonia (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).
On carefully removing a bit of the younger growth and examining it microscopically, it is found to consist of long filaments much like those ofVaucheria, 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 zoöspores, produced in great numbers in sporangia at the ends of the branches. The protoplasm collects here much as we saw inV. 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 appearancein 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 zoöspores 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 zoöspore, like those already described. By killing the zoöspores 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 zoöspores there are also resting spores developed. Oögonia like those ofVaucheriaor thePeronosporeæare formed usually after the formation of zoöspores 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]
The oögonia (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).
Thegreat majority of the plants ordinarily known asfungiare embraced under this head. While some of the lower forms show affinities with thePhycomycetes, and through them with the algæ, 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 theMycomycetes, 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 colorlesscell 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).
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 colorlesscell 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).
Fig. 37.Fig. 37.—A, single cells of yeast.B,C, similar cells, showing the process of budding, × 750.
Fig. 37.—A, single cells of yeast.B,C, similar cells, showing the process of budding, × 750.
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 theSmuts), which through cultivation have lost the power of developing further.
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.
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.
Fig. 38.Fig. 38.—A, “tassel” of corn attacked by smut (Ustillago).B, filaments of the fungus from a thin section of a diseased grain, showing the beginning of the formation of the spores, × 300.C, ripe spores, × 300.
Fig. 38.—A, “tassel” of corn attacked by smut (Ustillago).B, filaments of the fungus from a thin section of a diseased grain, showing the beginning of the formation of the spores, × 300.C, ripe spores, × 300.
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 remainingMycomycetesare pretty readily divisible into two great classes, based upon the arrangement of the spores. The first of these is known as theAscomycetes(Sac fungi), the other theBasidiomycetes(mushrooms, puff-balls, etc.).
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 commonAscomycetesbelong 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 (Perisporiaceæ), 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 (Podosphæra) 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 specimenswill show numerous brown or blackish specks scattered over the patches. These are the spore fruits.
Fig. 39.Fig. 39.—A, spore-bearing filaments of the dandelion mildew (Podosphæra), × 150.B, a germinating spore, × 150.C–F, development of the spore fruit, × 300.ar.archicarp.G, a ripe spore fruit, × 150.H, the spore sac removed from the spore fruit, × 150.I, spore-bearing filament attacked by another fungus (Cicinnobulus), causing the enlargement of the basal cell, × 150.J, a more advanced stage, × 300.K, spores, × 300.
Fig. 39.—A, spore-bearing filaments of the dandelion mildew (Podosphæra), × 150.B, a germinating spore, × 150.C–F, development of the spore fruit, × 300.ar.archicarp.G, a ripe spore fruit, × 150.H, the spore sac removed from the spore fruit, × 150.I, spore-bearing filament attacked by another fungus (Cicinnobulus), causing the enlargement of the basal cell, × 150.J, a more advanced stage, × 300.K, spores, × 300.
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 ofmuch-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).
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 ofmuch-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).
Fig. 40.Fig. 40.—Chrysanthemum mildew (Erysiphe), showing the suckers (h) by which the filaments are attached to the leaf.A, surface view.B, vertical section of the leaf, × 300.
Fig. 40.—Chrysanthemum mildew (Erysiphe), showing the suckers (h) by which the filaments are attached to the leaf.A, surface view.B, vertical section of the leaf, × 300.
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 fruitappears 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.
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 fruitappears 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.
Fig. 41.Fig. 41.—Forms of mildews (Erysiphe).A,Microsphæra, a spore fruit, × 150.B, cluster of spore sacs of the same, × 150.C, a single appendage, × 300.D, end of an appendage ofUncinula, × 300.E, appendage ofPhyllactinia, × 150.
Fig. 41.—Forms of mildews (Erysiphe).A,Microsphæra, a spore fruit, × 150.B, cluster of spore sacs of the same, × 150.C, a single appendage, × 300.D, end of an appendage ofUncinula, × 300.E, appendage ofPhyllactinia, × 150.
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 youngconidia, 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.
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 youngconidia, 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:Podosphæra, with a single ascus in the spore fruit; andErysiphe, 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).
Fig. 42.Fig. 42.—A, spore bearing filament of the herbarium mould (Eurotium), × 150.B,C, another species showing the way in which the spores are borne—optical section—× 150.D, spore fruit of the herbarium mould, × 150.E, spore sac.F, spores, × 300.G, spore-bearing filament of the common blue mould (Penicillium), × 300.sp.the spores.
Fig. 42.—A, spore bearing filament of the herbarium mould (Eurotium), × 150.B,C, another species showing the way in which the spores are borne—optical section—× 150.D, spore fruit of the herbarium mould, × 150.E, spore sac.F, spores, × 300.G, spore-bearing filament of the common blue mould (Penicillium), × 300.sp.the spores.
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.
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 ofEurotium, 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.
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 largerAscomycetes, 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 youngspore sacs colored a beautiful blue, so that they are readily distinguishable.
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 youngspore sacs colored a beautiful blue, so that they are readily distinguishable.
Fig. 43.Fig. 43.—A, a small cup fungus (Ascobolus), × 5.B, young spore fruit, × 300.ar.archicarp.C, an older one, × 150.ar.archicarp.sp.young spore sacs.D, section through a full-grown spore fruit (partly diagrammatic), × 25.sp.spore sacs.E, development of spore sacs and spores:i–iii, × 300;iv, × 150.F, ripe spores.G, a sterile filament (paraphysis), × 300.H, large scarlet cup fungus (Peziza), natural size.
Fig. 43.—A, a small cup fungus (Ascobolus), × 5.B, young spore fruit, × 300.ar.archicarp.C, an older one, × 150.ar.archicarp.sp.young spore sacs.D, section through a full-grown spore fruit (partly diagrammatic), × 25.sp.spore sacs.E, development of spore sacs and spores:i–iii, × 300;iv, × 150.F, ripe spores.G, a sterile filament (paraphysis), × 300.H, large scarlet cup fungus (Peziza), natural size.
The development of the spore sacs may be traced by carefully crushing the young spore fruits in water. The young spore sacs (Fig. 43,Ei) 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, andspreads out so as to expose the spore sacs as they discharge their contents (Fig. 43,D).
The development of the spore sacs may be traced by carefully crushing the young spore fruits in water. The young spore sacs (Fig. 43,Ei) 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, andspreads 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 genusPeziza(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.
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 algæ, 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 genusParmelia(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.
Fig. 44.Fig. 44.—A, a common lichen (Parmelia), of the natural size.ap.spore fruit.B, section through one of the spore fruits, × 5.C, section through the body of a gelatinous lichen (Collema), showing theNostocindividuals surrounded by the fungus filaments, × 300.D, a spermagonium ofCollema, × 25.E, a singleNostocthread.F, spore sacs and paraphyses ofUsnea, × 300.G,Protococcuscells and fungus filaments ofUsnea.
Fig. 44.—A, a common lichen (Parmelia), of the natural size.ap.spore fruit.B, section through one of the spore fruits, × 5.C, section through the body of a gelatinous lichen (Collema), showing theNostocindividuals surrounded by the fungus filaments, × 300.D, a spermagonium ofCollema, × 25.E, a singleNostocthread.F, spore sacs and paraphyses ofUsnea, × 300.G,Protococcuscells and fungus filaments ofUsnea.
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. Theyare 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 ofProtococcus, or some similar green algæ, 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.InFigure 45,H, is shown one of the so-called “Soredia,”[7]a group of the algæ, upon which the lichen is parasitic, surrounded by some of thefilaments, the whole separating spontaneously from the plant and giving rise to a new one.
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 ofProtococcus, or some similar green algæ, 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.
InFigure 45,H, is shown one of the so-called “Soredia,”[7]a group of the algæ, upon which the lichen is parasitic, surrounded by some of thefilaments, the whole separating spontaneously from the plant and giving rise to a new one.
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.
Fig. 45.Fig. 45.—Forms of lichens.A, a branch with lichens growing upon it, one-half natural size.B,Usnea, natural size.ap.spore fruit.C,Sticta, one-half natural size.D,Peltigera, one-half natural size.ap.spore fruit.E, a single spore fruit, × 2.F,Cladonia, natural size.G, a piece of bark from a beech, with a crustaceous lichen (Graphis) growing upon it, × 2.ap.spore fruit.H,Sorediumof a lichen, × 300.
Fig. 45.—Forms of lichens.A, a branch with lichens growing upon it, one-half natural size.B,Usnea, natural size.ap.spore fruit.C,Sticta, one-half natural size.D,Peltigera, one-half natural size.ap.spore fruit.E, a single spore fruit, × 2.F,Cladonia, natural size.G, a piece of bark from a beech, with a crustaceous lichen (Graphis) growing upon it, × 2.ap.spore fruit.H,Sorediumof a lichen, × 300.
According to their form, lichens are sometimes divided into the bushy (fruticose), leafy (frondose), incrusting (crustaceous), and gelatinous. Of the first, the long grayUsnea(Fig. 45,A,B), which drapes the branches of trees in swamps, is a familiar example; of the second,Parmelia,Sticta(Fig. 45,C) andPeltigera(D) are types; of the third,Graphis(G), common on the trunks of beech-trees, to which it closely adheres; andof the last,Collema(Fig. 44,C,D,E), a dark greenish, gelatinous form, growing on mossy tree trunks, and looking like a colony ofNostoc, which indeed it is, but differing from an ordinary colony in being penetrated everywhere by the filaments of the fungus growing upon it.
Fig. 46.Fig. 46.—Branch of a plum-tree attacked by black knot. Natural size.
Fig. 46.—Branch of a plum-tree attacked by black knot. Natural size.
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.
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 theAscomycetesare the “black fungi,”Pyrenomycetes, represented by the black knot of cherry and plum trees, shown inFigure 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 theDiscomycetes, 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.
TheBasidiomycetesinclude 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 lowerBasidiomycetesare the so-called rusts. The largerBasidiomycetesare 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.
Of the lowerBasidiomycetes, the rusts (Uredineæ) 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 withinthe 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.
Fig. 47.Fig. 47.—A, a branch of red cedar attacked by a rust (Gymnosporangium), causing a so-called “cedar apple,” × ½.B, spores of the same, one beginning to germinate, × 300.C, a spore that has germinated, each cell producing a short, divided filament (basidium), which in turn gives rise to secondary spores (sp.), × 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 (Arisæma), bearing the cluster cup (Æcidium) stage of a rust, × 2.G, vertical section through a young cluster cup.H, similar section through a mature one, × 50.I, germinating spores ofH, × 300.J, part of a corn leaf, with black rust, natural size.K, red rust spore of the wheat rust (Puccinia graminis), × 300.L, forms of black-rust spores:i,Uromyces;ii,Puccinia;iii,Phragmidium.
Fig. 47.—A, a branch of red cedar attacked by a rust (Gymnosporangium), causing a so-called “cedar apple,” × ½.B, spores of the same, one beginning to germinate, × 300.C, a spore that has germinated, each cell producing a short, divided filament (basidium), which in turn gives rise to secondary spores (sp.), × 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 (Arisæma), bearing the cluster cup (Æcidium) stage of a rust, × 2.G, vertical section through a young cluster cup.H, similar section through a mature one, × 50.I, germinating spores ofH, × 300.J, part of a corn leaf, with black rust, natural size.K, red rust spore of the wheat rust (Puccinia graminis), × 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. InFigure 47,F, is shown a bit of the leaf of the Indian turnip (Arisæma) 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).
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 theepidermis 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.
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.
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 generaMelampsora, andUromyces(Fig. 47,Li), have unicellular teleuto spores;Puccinia(ii) andGymnosporangium, two-celled spores;Triphragmium, three-celled; andPhragmidium(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 lowerBasidiomycetesare the large fungi of whichTremella(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 higherBasidiomycetes, the toadstools, mushrooms, etc., are the highest, and any common form will serve for study. One of the most accessible and easily studied forms isCoprinus, of which there are several species growing on the excrement of various herbivorous animals. They not infrequently appear onhorse manure that has been kept covered with a glass for some time, as described forAscobolus. 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.