There is no reason for doubt that in other of the Discomycetes the germination of the sporidia is very similar to that already seen and described, whilst in the Pyrenomycetes, as far as we are aware, although the production of germinating tubes is by no means difficult, development has not been traced beyond this stage.*

* In the very important observations made by Dr. Cunningham at Calcutta, on substances floating in the atmosphere, it appeared that the sporidia of many Sphæric actually germinated after being taken up by the air. The multitude of fungus spores which were observed in every case was quite extraordinary.

VIII.

SEXUAL REPRODUCTION.

THE existence of some sort of sexual reproduction in Fungi has long been suspected, although in earlier instances upon insufficient grounds; but of late years observations have multiplied and facts accumulated which leave no doubt of its existence. If the Saprolegnia are left out of the question as disputed Fungi, there still remain a number of well authenticated instances of the phenomena of copulation, and many other facts which indicate some sort of sexual relationship. The precise manner in which those minute bodies, so common amongst the Sphæronemei, which we prefer to call stylospores, perform their functions is still to a great extent a mystery; yet it is no longer doubted that certain species of Aposphæria, Phoma, Septoria, &c., are only conditions of some species of Sphæria, often developed and matured in close proximity to them on the same host. In Ecidium, Rastelia, &c., spermogonia are produced plentifully on or near the same spots on which the fructification appears, either simultaneously or at a later period.* The relation of Cytispora to Valsa was suspected by Fries very many years ago, and, as since demonstrated, with very good reason. All attempts, however, to establish anything like sexual reproduction in the higher forms of Hymenomycetes have at present been unsuccessful; and the same may be said of the Gasteromycetes; but in Ascomycetes and Physomycetes instances abound.

We know not whether any importance is to be attached to the

* M. Tulasne has devoted a chapter to the spermogonia of the Uredines in his memoir, to which we have already alluded.

views of M. A. S. Ersted,* which have not since been confirmed, but which have been cited with some approval by Professor de Bary, as to a trace of sexual organs in Hymenomycetes. He is supposed to have seen in Agaricus variabilis, P., oocysts or elongated reniform cells, which spring up like rudimentary branches of the filaments of the mycelium, and enclose an abundant protoplasm, if not even a nucleus. At the base of these oocysts appear the presumed antheridia, that is to say, one or two slender filaments, which generally turn their extremities towards the oocysts, and which more rarely are applied to them. Then, without ulteriorily undergoing any appreciable modifications, the fertile cell or oocyst becomes enveloped in a network of filaments of mycelium which proceed from the one which bears it, and this tissue forms the rudiments of the cap. The reality of some kind of fecundation in this circumstance, and the mode of the phenomena, if there is one, are for the present equally uncertain. If M. Ersted's opinion is confirmed, naturally the whole of the cap will be the product of fecundation. Probably Karsten (Bonplandia, 1862, p. 62) saw something similar in Agaricus campestris, but his account is obscure.

In Phycomyces the organs of reproduction have been subjected to close examination by Van Tieghem,† and although he failed to discover chlamydospores in this, he describes them in other Mucors. In this species, besides the regular sexual development, by means of sporangia, there is a so-called sexual reproduction by means of zygospores, which takes place in this wise. The threads which conjugate to form the zygospores are slender and erect on the surface of the substratum. Two of these threads come into close contact through a considerable length, and clasp each other by alternate protuberances and depressions. Some of the protuberances are prolonged into slender tubes. At the same time the free extremities of the threads dilate, and arch

* Eersted, in "Verhandl der König. Dän. Gesell. Der Wissensch," 1st January, 1865; De Bary, "Handbuch der Physiol. Botanik" (1866), p. 172; "Annales des Sci. Nat." (5me sér.), vol. v. (1866), p. 366.

+ Van Tieghem and Le Monnier, in “Annales des Sci. Nat.” (1873), vol. xvii.

P. 261.

over one towards the other until their tops touch like a vice, each limb of which rapidly increases in size. Each of these arcuate, clavate cells has now a portion of its extremity isolated by a partition, by means of which a new hemispherical cell is formed at the end of each thread at its point of junction with the opposed thread. These cells become afterwards cylindrical by pressure, the protoplasm is aggregated into a mass, the double membrane at the point of first contact is absorbed, and the two confluent masses of protoplasm form a zygospore invested with a tubercular coat and enveloped by the primary wall of the two

conjugating cells. During this formation of the zygospore, the two arched cells whence the zygospore originated develop a series of dichotomous processes in close proximity to the walls which separate them from the zygospore. These processes

appear at first on one of the arcuate cells in successive order. The first makes its appearance above upon the convex side; the succeeding ones to the right and left in descending order; the last is in the concavity beneath. It is only after the development of this that the first process appears on the opposite cell, which is followed by others in the same order. These dichotomous processes are nothing more than branches developed from the arcuate, or mother cells. During all these changes, while the zygospore

enlarges, the wall of the arcuate cells becomes coloured brown. This colouring is more marked on the convex side, and it shows itself first in the cell on which the dichotomous branches are first produced, and which retains the darker tint longer than the other. The zone from whence the processes issue, and also the processes themselves, have their walls blackened deeply, while the walls of the conjugated cells, which continue to clothe the zygospore during the whole of its development, are bluish-black. By pressure, the thin brittle coat which envelopes the zygospore is ruptured, and the coat of the zygospore exposed, formed of a thick cartilaginous membrane, studded with large irregular warts.

The germination of the zygospores in this species has not as yet been observed, but it is probably the same or very similar to that observed in other species of Mucor. In these the rough tuberculate epispore splits on one side, and its internal coat elongates itself and protrudes as a tube filled with protoplasm and oil globules, terminating in an ordinary sporangium. Usually the amount of nutriment contained in the zygospore is exhausted by the formation of the terminal sporangium, according to Brefeld; * but Van Tieghem and Le Monnier remark that in their examinations they have often seen a partition formed at about a third of the length of the principal filament from the base, below which a strong branch is given off, and this is also terminated by a large sporangium.

De Bary has given a precise account of the formation of the zygospore in another of the Mucors, Rhizopus nigricans, in which he says that the filaments which conjugate are solid rampant tubes, which are branched without order and confusedly intermingled. Where two of these filaments meet each of them pushes towards the other an appendage which is at first cylindrical and of the same diameter. From the first these two processes are applied firmly one to the other by their extremities; they increase in size, become clavate, and constitute together a fusiform body placed across the two conjugated filaments. Between the two halves of this body there exists no constant difference of size; often they are both perfectly equal. In each Brefeld, Bot. Unt. uber Schimmelpilze," p. 31.

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