M. C. Cooke

A great number of very interesting facts have during late years been brought to light of the different forms which fungi assume in the course of their development. At the same time, we fear that a great many assumptions have been accepted for fact, and supposed connections and relations between two or three or more so-called species, belonging to different genera, have upon insufficient data been regarded as so many states or conditions of one and the same plant. Had the very pertinent suggestions of Professor de Bary been more generally acted upon, these suspicions would have been baseless. His observations are so valuable as a caution, that we cannot forbear prefacing our own remarks on this subject by quoting them.[A] In order to determine, he says, whether an organic form, an organ, or an organism, belongs to the same series of development as another, or that which is the same is developed from it, or vice versÂ, there is only one way, viz., to observe how the second grows out of the first. We see the commencement of the second begin as a part of the first, perfect itself in connection with it, and at last it often becomes independent; but be it through spontaneous dismembering from the first, or that the latter be destroyed and the second remains, both their disunited bodies are always connected together in organic continuity, as parts of a whole (single one) that can cease earlier or later.

By observing the organic continuity, we know that the apple is the product of development of an apple-tree, and not hung on it by chance, that the pip of an apple is a product of the development of the apple, and that from the pip an apple-tree can at last be developed, that therewith all these bodies are members of a sphere of development or form. It is the same with every similar experience of our daily life, that where an apple-tree stands, many apples lie on the ground, or that in the place where apple-pips are sown seedlings, little apple-trees, grow out of the ground, is not important to our view of the course of development. Every one recognizes that in his daily life, because he laughs at a person who thinks a plum which lies under an apple-tree has grown on it, or that the weeds which appear among the apple seedlings come from apple-pips. If the apple-tree with its fruit and seed were microscopically small, it would not make the difference of a hair’s breadth in the form of the question or the method of answering it, as the size of the object can be of no importance to the latter, and the questions which apply to microscopical fungi are to be treated in the same manner.

If it then be asserted that two or several forms belong to a series of development of one kind, it can only be based on the fact of their organic continuity. The proof is more difficult than in large plants, partly because of the delicacy, minuteness, and fragility of the single parts, particularly the greater part of the mycelia, partly because of the resemblance of the latter in different species, and therefore follows the danger of confusing them with different kinds, and finally, partly in consequence of the presence of different kinds in the same substratum, and therefore the mixture not only of different sorts of mycelia, but also that different kinds of spores are sown. With some care and patience, these difficulties are in no way insurmountable, and they must at any rate be overcome; the organic continuity or non-continuity must be cleared up, unless the question respecting the course of development, and the series of forms of special kinds, be laid on one side as insolvable.

Simple and intelligible as these principles are, they have not always been acted upon, but partly neglected, partly expressly rejected, not because they were considered false, but because the difficulties of their application were looked upon as insurmountable. Therefore another method of examination was adopted; the spores of a certain form were sown, and sooner or later they were looked after to see what the seed had produced—not every single spore—but the seed en masse, that is, in other words, what had grown on that place where the seed had been sown. As far as it relates to those forms which are so widely spread, and above all grow in conjunction with one another—and that is always the case in the specimens of which we speak—we can never be sure that the spores of the form which we mean to test are not mingled with those of another species. He who has made an attentive and minute examination of this kind knows that we may be sure to find such a mixture, and that such an one was there can be afterwards decidedly proved. From the seed which is sown, these spores, for which the substratum was most suitable, will more easily germinate, and their development will follow the more quickly. The favoured germs will suppress the less favoured, and grow up at their expense. The same relation exists between them as between the seeds, germs, and seedlings of a sown summer plant, and the seeds which have been undesignedly sown with it, only in a still more striking manner, in consequence of the relatively quick development of the mildew fungus.

Therefore, that from the latter a decided form, or a mixture of several forms, is to be found sown on one spot, is no proof of their generic connection with one which has been sown for the purpose of experiments; and the matter will only be more confused if we call imagination to our aid, and place the forms which are found near one another, according to a real or fancied resemblance, in a certain series of development. All those statements on the sphere of form and connection, which have for their basis such a superficial work, and are not based on the clear exposition of the continuity of development, as by the origin of the connection of the Mucor with Penicillium, Oidium lactis and Mucor, Oidium and Penicillium, are rejected as unfounded.

A source of error, which can also interfere in the last-named superficial method of cultivation for experiments, is, viz., that heterogeneous unwished-for spores intrude themselves from without, among the seed which is sown, but that has been until now quite disregarded. It is of great importance in practice, but in truth, for our present purpose, synonymous with what we have already written. Those learned in the science of this kind of culture lay great stress on its importance, and many apparatuses have been constructed, called “purely cultivating machines,” for the purpose of destroying the spores which are contained in the substratum, and preventing the intrusion of those from without. The mixture in the seed which is sown has of course not been obviated. These machines may, perhaps, in every other respect, fulfil their purpose, but they cannot change the form of the question, and the most ingeniously constructed apparatus cannot replace the attention and intellect of the observer.[B]

Two distinct kinds of phenomena have been grouped under the term “polymorphy.” In one series two or more forms of fruit occur consecutively or simultaneously on the same individual, and in the other two or more forms appear on a different mycelium, on a different part of the same plant, or on a matrix wholly distinct and different; in the latter case the connection being attested or suspected circumstantially, in the former proved by the method suggested by De Bary. It will at once be conceded that in cases where actual growth and development substantiate the facts the polymorphy is undoubted, whilst in the other series it can at best be little more than suspected. We will endeavour to illustrate both these series by examples.

One of the first and earliest suspected cases of dualism, which long puzzled the older mycologists, was observed amongst the Uredines, and many years ago it was held that there must be some mysterious association between the “red rust” (Trichobasis ruligo vera) of wheat and grasses and the “corn mildew” (Puccinia graminis) which succeeded it. The simple spored rust first makes its appearance, and later the bilocular “mildew.” It is by no means uncommon to find the two forms in the same pustule. Some have held, without good reason, that the simple cells became afterwards divided and converted into Puccinia, but this is not the case; the uredo-spores are always simple, and remain so except in Uredo linearis, where every intermediate stage has been observed. Both are also perfect in their kind, and capable of germination.

What the precise relations between the two forms may be has as yet never been revealed to observers, but that the two forms belong to one species is not now doubted. Very many species of Puccinia have already been found associated with a corresponding Trichobasis, and of Phragmidium with a relative Lecythea, but it may be open to grave doubt whether some of the very many species associated by authors are not so classed upon suspicion rather than observation. We are ready to admit that the evidence is strong in favour of the dimorphism of a large number of species—it may be in all, but this awaits proof, or substantial presumption on good grounds. Up to the present we know that there are species of Trichobasis which have never been traced to association with a Puccinia, and doubtless there will be species of Puccinia for which no corresponding Uredo or Trichobasis can be found.

Tulasne remarks, in reference to Puccinia sonchi, in one of his memoirs, that this curious species exhibits, in effect, that a Puccinia may unite three sorts of reproductive bodies, which, taking part, constitute for the mycologists of the day three entirely different plants—a Trichobasis, a Uromyces, and a Puccinia. The Uredines are not less rich, he adds, in reproductive bodies of divers sorts than the Pyrenomycetes and the Discomycetes; and we should not be surprised at this, since it seems to be a law, almost constant in the general harmony of nature, that the smaller the organized beings are, the more their races are prolific.

In Puccinia variabilis, Grev., it is common to find a unicellular form, species of Trichobasis, in the same pustules. A like circumstance occurs with Puccinia violarum, Link., and Trichobasis violarum, B.; with Puccinia fallens, C., and Trichobasis fallens, Desm.; also with Puccinia menthÆ, P., and Trichobasis Labiatarum, D. C. In Melampsora, again, the prismatic pseudospores of Melampsora salicina, Lev., are the winter fruits of Lecythea caprearum, Lev., as those of Melampsora populina, Lev., are of Lecythea populina, Lev. In the species of Lecythea themselves will be found, as De Bary[C] has shown, hyaline cysts of a larger size, which surround the pseudospores in the pustules in which they are developed.

A good illustration of dimorphism in one of the commonest of moulds is given by De Bary in a paper from which we have already quoted.[D] He writes thus:—In every household there is a frequent unbidden guest, which appears particularly on preserved fruits, viz., the mould which is called Aspergillus glaucus. It shows itself to the naked eye as a woolly floccy crust over the substance, first purely white, then gradually covered with little fine glaucous, or dark green dusty heads. More minute microscopical examination shows that the fungus consists of richly ramified fine filaments, which are partly disseminated in the substratum, and partly raised obliquely over it. They have a cylindrical form with rounded ends, and are divided into long outstretched members, each of which possesses the property which legitimatizes it as a vesicle in the ordinary sense of the word; it contains, enclosed within a delicate structureless wall, those bodies which bear the appearance of a finely granulated mucous substance, which is designated by the name of protoplasm, and which either equally fills the cells, or the older the cell the more it is filled with watery cavities called vacuoles.

All parts are at first colourless. The increase in the length of the filaments takes place through the preponderating growth near their points; these continually push forward, and, at a short distance from them, successive new partitions rise up, but at a greater distance, the growth in the length ceases. This kind of growth is called point growth. The twigs and branches spring up as lateral dilatations of the principal filament, which, once designed, enlarges according to the point growth. This point growth of every branch is, to a certain extent, unlimited. The filaments in and on the substratum are the first existing members of the fungus; they continue so long as it vegetates. As the parts which absorb nourishment from and consume the substance, they are called the mycelium. Nearly every fungus possesses a mycelium, which, without regard to the specific difference of form and size, especially shows the described nature in its construction and growth.

The superficial threads of the mycelium produce other filaments beside those numerous branches which have been described, and which are the fruit thread (carpophore) or conidia thread. These are on an average thicker than the mycelium threads, and only exceptionally ramified or furnished with partitions; they rise almost perpendicularly into the air, and attain a length of, on an average, half a millimetre, or one-fiftieth of an inch, but they seldom become longer, and then their growth is at an end. Their free upper end swells in a rounded manner, and from this is produced, on the whole of its upper part, rayed divergent protuberances, which attain an oval form, and a length almost equal to their radius, or, in weaker specimens, the diameter of the rounded head. The rayed divergent protuberances are the direct producers and bearers of the propagating cells, spores, or conidia, and are called sterigmata. Every sterigma at first produces at its point a little round protuberance, which, with a strong narrow basis, rests upon the sterigma. These are filled with protoplasm, swell more and more, and, after some time, separate themselves by a partition from the sterigma into independent cells, spores, or conidia.

The formation of the first spore takes place at the same end of the sterigma, and in the same manner a second follows, then a third, and so on; every one which springs up later pushes its predecessor in the direction of the axis of the sterigma in the same degree in which it grows itself; every successive spore formed from a sterigma remains for a time in a row with one another. Consequently every sterigma bears on its apex a chain of spores, which are so much the older, the farther they stand from the sterigma. The number of the links in a chain of spores reaches in normal specimens to ten or more. All sterigmata spring up at the same time, and keep pace with one another in the formation of the spores. Every spore grows for a time, according to its construction, and at last separates itself from its neighbours. The mass of dismembered spores forms that fine glaucous hue which is mentioned above. The spores, therefore, are articulated in rows, one after the other, from the ends of the sterigmata. The ripe spore, or conidium, is a cell of a round or broadly oval form, filled with a colourless protoplasm, and, if observed separately, is found to be provided with a brownish, finely verruculose, dotted wall.

Fig. 102.—a. Aspergillus glaucus; b. conidia; c. germinating conidium; d. conceptacle of Eurotium; e. ascus.

The same mycelium which forms the pedicel for the conidia when it is near the end of its development, forms by normal vegetation a second kind of fructification. It begins as delicate thin little branches, which are not to be distinguished by the naked eye, and which mostly in four or six turns, after a quickly terminated growth, wind their ends like a corkscrew. (Fig. 102.) The sinuations decrease in width more and more, till they at last reach close to one another, and the whole end changes from the form of a corkscrew into that of a hollow screw. In and on that screw-like body, a change of a complicated kind takes place, which is a productive process. In consequence of this, from the screw body a globose receptacle is formed, consisting of a thin wall of delicate cells, and a closely entwined row of cells surrounded by this dense mass (d). By the enlargement of all these parts the round body grows so much, that by the time it is ripe it is visible to the naked eye. The outer surface of the wall assumes a compactness and a bright yellow colour; the greater part of the cells of the inner mass become asci for the formation of sporidia, while they free themselves from the reciprocal union, take a broad oval form, and each one produces within its inner space eight sporidia (e). These soon entirely fill the ascus. When they are quite ripe, the wall of the conceptacle becomes brittle, and from irregular fissures, arising easily from contact, the colourless round sporidia are liberated.

The pedicels of both kinds of fruit are formed from the same mycelium in the order just described. If we examine attentively, we can often see both springing up close to one another from the same filament of a mycelium. This is not very easy in the close interlacing of the stalks of a mass of fungi in consequence of their delicacy and fragility. Before their connection was known, the conceptacles and the conidia pedicels were considered as organs of two very different species of fungi. The conceptacles were called Eurotium herbariorum, and the conidia bearers were called Aspergillus glaucus.

Allied to Eurotium is the group of Erysiphei, in which well-authenticated polymorphy prevails. These fungi are developed on the green parts of growing plants, and at first consist of a white mouldy stratum, composed of delicate mycelium, on which erect threads are produced, which break up into subglobose joints or conidia. The species on grass was named Oidium monilioides before its relationship was known, but undoubtedly this is only the conidia of Erysiphe graminis. In like manner the vine disease (Oidium Tuckeri) is most probably only the conidia of a species of Erysiphe, of which the perfect condition has not yet been discovered. On roses the old Oidium leucoconium is but the conidia of SphÆrotheca pannosa, and so of other species. The Erysiphe which ultimately appears on the same mycelium consists of globose perithecia, externally furnished with thread-like appendages, and internally with asci containing sporidia. In this genus there are no less than five different forms of fruit,[E] the multiform threads on the mycelium, already alluded to as forms of Oidium, the asci contained in the sporangia, which is the proper fruit of the Erysiphe, larger stylospores which are produced in other sporangia, the smaller stylospores which are generated in the pycnidia, and separate sporules which are sometimes formed in the joints of the necklaces of the conidia. These forms are figured in the “Introduction to Cryptogamic Botany” from SphÆrotheca Castagnei, which is the hop mildew.[F] The vine disease, hop mildew, and rose mildew, are the most destructive species of this group, and the constant annoyance of cultivators.

When first describing an allied fungus found on old paper, and named Ascotricha chartarum, the Rev. M. J. Berkeley called attention to the presence of globose conidia attached to the threads which surround the conceptacles,[G] and this occurred as long since as 1838. In a recent species of ChÆtomium found on old sacking, ChÆtomium griseum, Cooke,[H] we have found tufts in all respects similar externally to the ChÆtomium, but no perithecium was formed, naked conidia being developed apparently at the base of the coloured threads. In ChÆtomium funicolum, Cooke, a black mould was also found which may possibly prove to be its conidia, but at present there is no direct evidence.

The brothers Tulasne have made us acquainted with a greater number of instances amongst the SphÆriacei in which multiple organs of reproduction prevail. Very often old and decaying individuals belonging to species of Boletus will be found filled, and their entire substance internally replaced, by the threads and multitudinous spores of a golden yellow parasite, to which the name of Sepedonium chrysospermum has been given. According to Tulasne, this is merely a condition of a sphÆriaceous fungus belonging to his genus Hypomyces.[I]

The same observers also first demonstrated that Trichoderma viride, P., was but the conidia-bearing stage of Hypocrea rufa, P., another sphÆriaceous fungus. The ascigerous stroma of the latter is indeed frequently associated in a very close manner with the cushions of the pretended Trichoderma, or in other cases the same stroma will give rise to a different apparatus of conidia, of which the principal elements are acicular filaments, which are short, upright, and almost simple, and which give rise to small oval conidia which are solitary on the tips of the threads. Therefore this Hypocrea will possess two different kinds of conidia, as is the case in many species of Hypomyces.

A most familiar instance of dualism will be found in Nectria cinnabarina, of which the conidia form is one of the most common of fungi, forming little reddish nodules on all kinds of dead twigs.[J]

Almost any small currant twig which has been lying on the ground in a damp situation will afford an opportunity of studying this phenomenon. The whole surface of the twig will be covered from end to end with little bright pink prominences, bursting through the bark at regular distances, scarcely a quarter of an inch apart. Towards one end of the twig probably the prominences will be of a deeper, richer colour, like powdered cinnabar. The naked eye is sufficient to detect some difference between the two kinds of pustules, and where the two merge into each other specks of cinnabar will be visible on the pink projections. By removing the bark it will be seen that the pink bodies have a sort of paler stem, which spreads above into a somewhat globose head, covered with a delicate mealy bloom. At the base it penetrates to the inner bark, and from it the threads of mycelium branch in all directions, confined, however, to the bark, and not entering the woody tissues beneath. The head, placed under examination, will be found to consist of delicate parallel threads compacted together to form the stem and head. Some of these threads are simple, others are branched, bearing here and there upon them delicate little bodies, which are readily detached, and which form the mealy bloom which covers the surface. These are the conidia, little slender cylindrical bodies, rounded at the ends.

Passing to the other bodies, which are of a deeper colour, it will soon be discovered that, instead of being simple rounded heads, each tubercle is composed of numerous smaller, nearly globose bodies, closely packed together, often compressed, all united to a base closely resembling the base of the other tubercles. If for a moment we look at one of the tubercles near the spot where the crimson tubercles seem to merge into the pink, we shall not only find them particoloured, but that the red points are the identical globose little heads just observed in clusters. This will lead to the suspicion, which can afterwards be verified, that the red heads are really produced on the stem or stroma of the pink tubercles.

A section of one of the red tubercles will show us how much the internal structure differs. The little subglobose bodies which spring from a common stroma or stem are hollow shells or capsules, externally granular, internally filled with a gelatinous nucleus. They are, indeed, the perithecia of a sphÆriaceous fungus of the genus Nectria, and the gelatinous nucleus contains the fructification. Still further examination will show that this fructification consists of cylindrical asci, each enclosing eight elliptical sporidia, closely packed together, and mixed with slender threads called paraphyses.

Here, then, we have undoubted evidence of Nectria cinnabarina, with its fruit, produced in asci growing from the stroma or stem, and in intimate relationship with what was formerly named Tubercularia vulgaris. A fungus with two forms of fruit, one proper to the pink, or Tubercularia form, with naked slender conidia, the other proper to the mature fungus, enclosed in asci, and generated within the walls of a perithecium. Instances of this kind are now known to be far from uncommon, although they cannot always, or often, be so clearly and distinctly traced as in the illustration which we have selected.

It is not uncommon for the conidia of the SphÆria to partake of the characteristics of a mould, and then the perithecia are developed amongst the conidial threads. A recently recorded instance of this relates to SphÆria Epochnii, B. and Br.,[L] the conidia form of which was long known before the SphÆria related to it was discovered, under the name of Epochnium fungorum. The Epochnium forms a thin stratum, which overruns various species of Corticium. The conidia are at first uniseptate. The perithecia of the SphÆria are at first pale bottle-green, crowded in the centre of the Epochnium, then black green granulated, sometimes depressed at the summit, with a minute pore. The sporidia are strongly constricted in the centre, at first uniseptate, with two nuclei in each division.

Another SphÆria in which the association is undoubted is the SphÆria aquila, Fr.,[M] which is almost always found nestling in a woolly brown subiculum, for the most part composed of barren brown jointed threads. These threads, however, produce, under favourable conditions, mostly before the perfection of the perithecia, minute subglobose conidia, and in this state constitute what formerly bore the name of Sporotrichum fuscum, Link., but now recognized as the conidia of SphÆria aquila.

In SphÆria nidulans, Schw., a North American species, we have more than once found the dark brown subiculum bearing large triseptate conidia, having all the characters of the genus Helminthosporium. In SphÆria pilosa, P., Messrs. Berkeley and Broome have observed oblong conidia, rather irregular in outline, terminating the hairs of the perithecium.[N] The same authors have also figured the curious pentagonal conidia springing from flexuous threads accompanying SphÆria felina, Fckl.,[O] and also the threads resembling those of a Cladotrichum with the angular conidia of SphÆria cupulifera, B. and Br.[P] A most remarkable example is also given by the Brothers Tulasne in Pleospora polytricha, in which the conidia-bearing threads not only surround, but grow upon the perithecia, and are crowned by fascicles of septate conidia.[Q]

Instances of this kind have now become so numerous that only a few can be cited as examples of the rest. It is not at all improbable that the majority of what are now classed together as species under the genus of black moulds, Helminthosporium, will at some not very distant period be traced as the conidia of different species of ascomycetous fungi. The same fate may also await other allied genera, but until this association is established, they must keep the rank and position which has been assigned to them.

Another form of dualism, differing somewhat in character from the foregoing, finds illustration in the sphÆriaceous genus Melanconis, of Tulasne, in which the free spores are still called conidia, though in most instances produced in a sort of spurious conceptaculum, or borne on short threads from a kind of cushion-shaped stroma. In the Melanconis stilbostoma,[R] there are three forms, one of slender minute bodies, oozing out in the form of yellow tendrils, which may be spermatia, formerly called Nemaspora crocea. Then there are the oval brown or olive brown conidia, which are at first covered, then oozing out in a black pasty mass, formerly Melanconium bicolor, and finally the sporidia in asci of SphÆria stilbostoma, Fries. In Melanconis Berkeleii, Tul., the conidia are quadrilocular, previously known as Stilbospora macrosperma, B. and Br. In a closely-allied species from North America, Melanconis bicornis, Cooke, the appendiculate sporidia are similar, and the conidia would also appear to partake of the character of Stilbospora. We may remark here that we have seen a brown mould, probably an undescribed species of Dematiei, growing in definite patches around the openings in birch bark caused by the crumpent ostiola of the perithecia of Melanconis stilbostoma, from the United States.

In Melanconis lanciformis,[S] Tul., there are, it would appear, four forms of fruit. One of these consists of conidia, characterized by Corda as Coryneum disciforme.[T] Stylospores, which are also figured by Corda under the name of Coniothecium betulinum; pycnidia,[U] first discovered by Berkeley and Broome, and named by them Hendersonia polycystis;[V] and the ascophorous fruits which constituted the SphÆria lanciformis of Fries. Mr. Currey indicated Hendersonia polycystis, B. and Br., as a form of fruit of this species in a communication to the Royal Society in 1857.[W] He says this plant grows upon birch, and is in perfection in very moist weather, when it may be recognized by the large black soft gelatinous protuberances on the bark, formed by spores escaping and depositing themselves upon and about the apex of the perithecium. This I suspect to be an abnormal state of a well-known SphÆria (S. lanciformis), which grows upon birch, and upon birch only.

We might multiply, almost indefinitely, instances amongst the SphÆriacei, but have already given sufficient for illustration, and will therefore proceed briefly to notice some instances amongst the Discomycetes, which also bear their complete or perfect fruit in asci.

The beautiful purple stipitate cups of Bulgaria sarcoides, which may be seen flourishing in the autumn on old rotten wood, are often accompanied by club-shaped bodies of the same colour; or earlier in the season these clavate bodies may be found alone, and at one time bore the name of Tremella sarcoides. The upper part of these clubs disseminate a great abundance of straight and very slender spermatia. Earlier than this they are covered with globose conidia. The fully-matured Bulgaria develops on its hymenium clavate delicate asci, each enclosing eight elongated hyaline sporidia, so that we have three forms of fruit belonging to the same fungus, viz. conidia and spermatia in the Tremella stage, and sporidia contained in asci in the mature condition.[X] The same phenomena occur with Bulgaria purpurea, a larger species with different fruit, long confounded with Bulgaria sarcoides.

On the dead stems of nettles it is very common to meet with small orange tubercles, not much larger than a pin’s head, which yield at this stage a profusion of slender linear bodies, produced on delicate branched threads, and at one time bore the name of Dacrymyces UrticÆ, but which are now acknowledged to be only a condition of a little tremelloid Peziza of the same size and colour, which might be mistaken for it, if not examined with the microscope, but in which there are distinct asci and sporidia. Both forms together are now regarded as the same fungus, under the name of Peziza fusarioides, B.

The other series of phenomena grouped together under the name of polymorphism relate to forms which are removed from each other, so that the mycelium is not identical, or, more usually, produced on different plants. The first instance of this kind to which we shall make reference is one of particular interest, as illustrative of the old popular creed, that berberry bushes near corn-fields produced mildewed corn. There is a village in Norfolk, not far from Great Yarmouth, called “Mildew Rollesby,” because of its unenviable notoriety in days past for mildewed corn, produced, it was said, by the berberry bushes, which were cut down, and then mildew disappeared from the corn-fields, so that Rollesby no longer merited its sobriquet. It has already been shown that the corn-mildew (Puccinia graminis) is dimorphous, having a one-celled fruit (Trichobasis), as well as a two-celled fruit (Puccinia). The fungus which attacks the berberry is a species of cluster-cup (Æcidium berberidis), in which little cup-like peridia, containing bright orange pseudospores, are produced in tufts or clusters on the green leaves, together with their spermogonia.

De Bary’s observations on this association of forms were published in 1865.[Y] In view of the popular belief, he determined to sow the spores of Puccinia graminis on the leaves of the berberry. For this purpose he selected the septate resting spores from Poa pratensis and Triticum repens. Having caused the spores to germinate in a moist atmosphere, he placed fragments of the leaves on which they had developed their secondary spores on young but full-grown berberry leaves, under the same atmospheric conditions. In from twenty-four to forty-eight hours a quantity of the germinating threads had bored through the walls and penetrated amongst the subjacent cells. This took place both on the upper and under surface of the leaves. Since, in former experiments, it appeared that the spores would penetrate only in those cases where the plant was adapted to develop the parasite, the connection between P. graminis and Æcid. berberidis seemed more than ever probable. In about ten days the spermogonia appeared. After a time the cut leaves began to decay, so that the fungus never got beyond the spermogonoid stage. Some three-year-old seedlings were then taken, and the germinating resting spores applied as before. The plants were kept under a bell-glass from twenty-four to forty-eight hours, and then exposed to the air like other plants. From the sixth to the tenth day, yellow spots appeared, with single spermogonia; from the ninth to the twelfth, spermogonia appeared in numbers on either surface; and, a few days later, on the under surface of the leaves, the cylindrical sporangia of the Æcidium made their appearance, exactly as in the normally developed parasite, except that they were longer, from being protected from external agents. The younger the leaves, the more rapid was the development of the parasite, and sometimes, in the younger leaves, the luxuriance was far greater than in free nature. Similar plants, to the number of two hundred, were observed in the nursery, and though some of them had Æcidium pustules, not one fresh pustule was produced; while two placed under similar circumstances, but without the application of any resting spores, remained all the summer free from Æcidium. It seems, then, indubitable so far that Æcidium berberidis does spring from the spores of Puccinia graminis.

It has, however, to be remarked that De Bary was not equally successful in producing the Puccinia from the spores of the Æcidium. In many cases the spores do not germinate when placed on glass, and they do not preserve their power of germinating very long. He reverts then to the evidence of experiments instituted by agriculturists. BÖnninghausen remarked, in 1818, that wheat, rye, and barley which were sown in the neighbourhood of a berberry bush covered with Æcidium contracted rust immediately after the maturation of the spores of the Æcidia. The rust was most abundant where the wind carried the spores. The following year the same observations were repeated; the spores of the Æcidium were collected, and applied to some healthy plants of rye. After five or six days these plants were affected with rust, while the remainder of the crop was sound. In 1863 some winter rye was sown round a berberry bush, which in the following year was infested with Æcidium, which was mature in the middle of May, when the rye was completely covered with rust. Of the wild grasses near the bush, Triticum repens was most affected. The distant plants of rye were free from rust.

The spores of the Æcidium would not germinate on berberry leaves; the berberry Æcidium could not therefore spring from the previous Æcidium. The uredospores of Puccinia graminis on germinating penetrate into the parenchym of the grass on which they are sown; but on berberry leaves, if the tips of the threads enter for a short distance into the stomates their growth at once ceases, and the leaves remain free from parasites.

Montagne has, however, described a Puccinia berberidis on leaves of Berberis glauca from Chili, which grows in company with Æcidium berberidis. This at first sight seems to contradict the above conclusions; but the Æcidium which from the same disc produces the puccinoid resting spores, appears to be different from the European species, inasmuch as the cells of the wall of the sporangium are twice as large, and the spores decidedly of greater diameter.[Z] The resting spores, moreover, differ not only from those of Puccinia graminis, but from those of all other European species.

From this account, then, it is extremely probable that the Æcidium of the berberry enters into the cycle of existence of Puccinia graminis, and, if this be true, wherefore should not other species of Puccinia be related in like manner to other Æcidia? This is the conclusion to which many have arrived, and, taking advantage of certain presumptions, have, we fear, rashly associated many such forms together without substantial evidence. On the leaves of the primrose we have commonly a species of Æcidium, Puccinia, and Uromyces nearly at the same time; we may imagine that all these belong to one cycle, but it has not yet been proved. Again, Uromyces cacaliÆ, Unger, Uredo cacaliÆ, Unger, and Æcidium cacaliÆ, Thumen, are considered by Heufler[a] to form one cycle. Numerous others are given by Fuckel,[b] and De Bary, in the same memoir from which we have already cited, notes Uromyces appendiculatus, Link., U. phaseolorum, Tul., and Puccinia tragopogonis, Ca., as possessing five kinds of reproductive organs. Towards the end of the year, shortly stipitate spores appear on their stroma, which do not fall off. These spores, which do not germinate till after a shorter or longer winter rest, may conveniently be called resting spores, or, as De Bary calls them, teleutospores, being the last which are produced. These at length germinate, become articulated, and produce ovate or kidney-shaped spores, which in their turn germinate, penetrating the cuticle of the mother plant, avoiding the stomates or apertures by which it breathes. After about two or three weeks, the mycelium, which has ramified among the tissues, produces an Æcidium, with its constant companion, spermogonia—distinct cysts, that is, from which a quantity of minute bodies ooze out, often in the form of a tendril, the function of which is imperfectly known at present, but which from analogy we regard as a form of fruit, though it is just possible that they may be rather of the nature of spermatozoids. The Æcidia contain, within a cellular membranous sac, a fructifying disc, which produces necklaces of spores, which ultimately separate from each other in the form of a granular powder. The grains of which it is composed germinate in their turn, no longer avoiding the stomates as before, but penetrating through their aperture into the parenchym. The new resultant mycelium reproduces the Uredo, or fifth form of fructification, and the Uredo spores fall off like those of the Æcidium, and in respect of germination, and mode of penetration, present precisely the same phenomena. The disc which has produced the Uredo spores now gives rise to the resting spores, and so the cycle is complete.[c]

The late Professor Œrsted, of Copenhagen, was of opinion that he had demonstrated the polymorphy of the Tremelloid Uredines, and satisfied himself that the one condition known as Podisoma was but another stage of Roestelia.[d] Some freshly gathered specimens of Gymnosporangium were damped with water, and during the night following the spores germinated profusely, so that the teleutospores formed an orange-coloured powder. A little of this powder was placed on the leaves of five small sorbs, which were damped and placed under bell-glasses. In five days yellow spots were seen on the leaves, and in two days more indications of spermogonia. The spermatia were discharged, and in two months from the first sowing, the peridia of Roestelia appeared, and were developed. “This trial of spores,” says Œrsted, “has conduced to the result expected, and proves that the teleutospores of Gymnosporangium, when transported upon the sorb, give rise to a totally different fungus, the Roestelia cornuta, that is to say, that an alternate generation comes between these fungi. They appertain in consequence to a single species, and the Gymnosporangium ceased to be an independent species, and must be considered as synonymous with the first generation of Roestelia. The spores have been transported upon young shoots of the juniper-tree, and have now commenced to produce some mycelium in the bark. There is no doubt that in next spring it will result in Gymnosporangium.”

Subsequently the same learned professor instituted similar experiments upon other hosts, with the spores of Podisoma, and from thence he concluded that Roestelia and Podisoma, in all their known species, were but forms the one of the other. Hitherto we are not aware that these results have been confirmed, or that the sowing of the spores of Roestelia on juniper resulted in Podisoma. Such experiments should be received always with care, and not too hastily accepted in their apparent results as proven facts. Who shall say that Roestelia would not have appeared on Sorbus within two months without the sowing of Podisoma spores?—because it is not by any means uncommon for that fungus to appear upon that plant. It is true many mycologists write and speak of Roestelia and Podisoma (or Gymnosporangium) as identical; but, as we think, without the evidence being so complete as to be beyond suspicion. It is, nevertheless, a curious fact that in Europe the number of species of Roestelia and Podisoma are equal, if one species be excluded, which is certainly not a good Podisoma, for the reception of which a new genus has been proposed.[e]

Amongst the ascigerous fungi will be found a curious but interesting genus formerly called Cordyceps, but for which Tulasne, in consequence of the discovery of secondary forms of fruit, has substituted that of Torrubia.[f] These curious fungi partake more or less of a clavate form, and are parasitic on insects. The pupÆ of moths are sometimes seen bearing upon them the white branched mould, something like a Clavaria in appearance, to which the name of Isaria farinosa has been given. According to Tulasne, this is the conidia form of the bright scarlet, club-shaped body which is also found on dead pupÆ, called Torrubia militaris. An American mould of the same genus, Isaria sphingum, found on mature moths,[g] is in like manner declared to be the conidia of Torrubia sphingum; whereas a similar mould, found on dead spiders, called Isaria arachnophila,[h] is probably of a similar nature. An allied kind of compact mould, which is parasitic on Cocci, on the bark of trees, recently found in England by Mr. C. E. Broome, and named Microcera coccophila,[i] is said by Tulasne to be a condition of SphÆrostilbe, and it is intimated that other productions of a similar character bear like relations to other sphÆriaceous fungi. For many species of Torrubia no corresponding conidia are yet known.

Some instances might be noted, not without interest, in which the facts of dimorphism or polymorphism have not been satisfactorily proved, but final judgment is held in suspense until suspicion is replaced by conviction. Some years since, a quantity of dead box leaves were collected, on which flourished at the time a mould named Penicillium roseum. This mould has a roseate tint, and occurs in patches on the dead leaves lying upon the ground; the threads are erect and branched above, bearing chains of oblong, somewhat spindle-shaped spores, or, perhaps more accurately, conidia. When collected, these leaves were examined, and nothing was observed or noted upon them except this Penicillium. After some time, certainly between two and three years, during which period the box remained undisturbed, circumstances led to the examination again of one or two of the leaves, and afterwards of the greater number of them, when the patches of Penicillium were found to be intermixed with another mould of a higher development, and far different character. This mould, or rather Mucor, consists of erect branching threads, many of the branches terminating in a delicate globose, glassy head, or sporangium, containing numerous very minute subglobose sporidia. This species was named Mucor hyalinus.[j] The habit is very much like that of the Penicillium, but without any roseate tint. It is almost certain that the Mucor could not have been present when the Penicillium was examined, and the leaves on which it had grown were enclosed in the tin box, but that the Mucor afterwards appeared on the same leaves, sometimes from the same patches, and, as it would appear, from the same mycelium. The great difference in the two species lies in the fructification. In the Penicillium, the spores are naked, and in moniliform threads; whilst in Mucor the spores are enclosed within globose membraneous heads or sporangia. Scarcely can we doubt that the Mucor alluded to above, found thus intermixed, under peculiar circumstances, with Penicillium roseum, is no other than the higher and more complete form of that species, and that the Penicillium is only its conidiiferous state. The presumption in this case is strong, and not so open to suspicion as it would be did not analogy render it so extremely probable that such is the case, apart from the fact of both forms springing from the same mass of mycelium. In such minute and delicate structures it is very difficult to manipulate the specimens so as to arrive at positive evidence. If a filament of mycelium could be isolated successfully, and a fertile thread, bearing the fruit of each form, could be traced from the same individual mycelium thread, the evidence would be conclusive. In default of such conclusive evidence, we are compelled to rest with assumption until further researches enable us to record the assumption as fact.[k]

Apropos of this very connection of Penicillium with Mucor, a similar suspicion attaches to an instance noted by a wholly disinterested observer to this effect. “On a preparation preserved in a moist chamber, on the third day a white speck was seen on the surface, consisting of innumerable ‘yeast’ cells, with some filaments, branching in all directions. On the fourth day tufts of Penicillium, had developed two varieties—P. glaucum and P. viride. This continued until the ninth day, when a few of the filaments springing up in the midst of the Penicillium were tipped with a dewdrop-like dilatation, excessively delicate—a mere distended pellicle. In some cases they seemed to be derived from the same filament as others bearing the ordinary branching spores of Penicillium, but of this I could not be positive. This kind of fructification increased rapidly, and on the fourteenth day spores had undoubtedly developed within the pellicle, just as had been observed in a previous cultivation, precisely similar revolving movements being also manifested.”[l] Although we have here another instance of Mucor and Penicillium growing in contact, the evidence is insufficient to warrant more than a suspicion of their identity, inasmuch as the equally minute spores of Mucor and Penicillium might have mingled, and each producing its kind, no relationship whatever have existed between them, except their development from the same matrix.

Another case of association—for the evidence does not proceed further—was recorded by us, in which a dark-coloured species of Penicillium was closely associated with what we now believe to be a species of Macrosporium—but then designated a Sporidesmium—and a minute SphÆria growing in succession on damp wall-paper. Association is all that the facts warrant us in calling it.

We cannot forbear alluding to one of the species of SphÆria to which Tulasne[m] attributes a variety of forms of fruit, and we do so here because we think that a circumstance so extraordinary should be confirmed before it is accepted as absolutely true. This refers to the common SphÆria found on herbaceous plants, known as SphÆria (Pleospora) herbarum. First of all the very common mould called Cladosporium herbarum is constituted as conidia, and of this again Macrosporium sarcinula, Berk., is considered to be another condition. In the next place, Cytispora orbicularis, Berk., and Phoma herbarum, West., are regarded as pycnidia, enclosing stylospores. Then Alternaria tenuis, Pr.,[n] which is said to be parasitic on Cladosporium herbarum, is held to be only a form of that species, so that here we have (including the perithecia) no less than six forms or phases for the same fungus. As Macrosporium Cheiranthi, Pr., often is found in company with Cladosporium herbarum, that is also open to suspicion.

We have adduced in the foregoing pages a few instances which will serve to illustrate the polymorphism of fungi. Some of these it will be observed are accepted as beyond doubt, occurring as they do in intimate relationship with each other. Others are considered as scarcely so well established, but probable, although developed sometimes on different species of plants. Finally, some are regarded as hitherto not satisfactorily proved, or, it may be, only suspicious. In this latter group, however much probability may be in their favour, it can hardly be deemed philosophical to accept them on such slender evidence as in some cases alone is afforded. It would not have been difficult to have extended the latter group considerably by the addition of instances enumerated by various mycologists in their works without any explanation of the data upon which their conclusions have been founded. In fact, altogether this chapter must be accepted as illustrative and suggestive, but by no means as exhaustive.