Part 21

Van Tieghem and Le Monnier, in "Annales des Sci. Nat." (1873), vol. xvii. p. 261.

Brefeld, "Bot. Unt. uber Schimmelpilze," p. 31.

De Bary, "Morphologie und Physiologie der Pilze," cap. 5, p. 160; "Ann. des Sci. Nat." (1866), p. 343.

Cornu, in "Ann. des Sci. Nat." (5^me sér.), vol. xv. p. 1 (1872).

Pringsheim's "Jahrbucher," vol. ii. p. 169.

De Bary, in "Annales des Sciences Naturelles" (5^me sér.), vol. v. (1866), p. 343; Hoffmeister's "Handbook" (Fungi), cap. v. p. 155.

De Bary, in "Annales des Sci. Nat." (4^me sér.), vol. xx. p. 129.

De Bary, in "Annales des Sciences Naturelles" (5^me sér.), p. 343.

Woronin, in De Bary's "Beitr. zur. Morph. und Physiol. der Pilze," ii. (1866), pp. 1-11.

Tulasne, "Ann. des Sci. Nat." (5^me sér.), October, 1866, p. 211.

Tulasne, "On the Phenomena of Copulation in certain Fungi," in "Ann. des Sci. Nat." (1866), p. 211.

De Bary, "Morphologie und Phys. der Pilze," cap. v., p. 162.

Berkeley, in "Journ. Hort. Soc." vol ii. p. 107; Tulasne, "Ann. d. Sc. Nat." (4^me sér.), vol. ii. tab. 12.

Tulasne, "New Researches on the Reproductive Apparatus of Fungi;" "Comptes Rendus," vol. xxxv. (1852), p. 841.

De Bary, "Morphologie und Physiologie der Pilze," cap. v. p. 168.

IX.

POLYMORPHISM.

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. 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.

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 has shown, hyaline cysts of a larger size, which surround the pseudospores in the pustules in which they are developed.