Another method of reproduction, not uncommon in Mucorini, is described by Van Tieghem in this species. Conjugating threads on the substratum by degrees elaborate zygospores, but these, contrary to the mode in other species, are surrounded by curious branched processes which emanate from the arcuate cells on either side of the newly-developed zygospore. This system of reproduction is again noticed more in detail in the chapter on polymorphism.
M. de Seynes has given the details of his examination of the sporidia of Morchella esculenta during germination.[O] A number of these sporidia, placed in water in the morning, presented, at nine o’clock of the same evening, a sprout from one of the extremities, measuring half the length of the spore. In the morning of the next day this sprout had augmented, and become a filament three or four times as long. The next day these elongated filaments exhibited some transverse divisions and some ramifications. On the third day, the germination being more advanced, many more of the sporidia were as completely changed, and presented, in consequence of the elongation, the appearance of a cylindrical ruffle, the cellular prolongations arising from the germination having a tendency towards one of the extremities of the longer axis of the sporidium, and more often to the two opposed extremities, either simultaneously or successively. Out of many hundreds of sporidia examined during germination, he had only seen a very few exceptions to this rule, among which he had encountered the centrifugal tendency to vegetate by two opposed filaments, proving that if it bears a second by the side of the primal filament situated at one of the poles, a second would also be seen from the side of the filament coming from the opposite pole.
Before being submitted to the action of water, the contents of the sporidia seemed formed of two distinct parts, one big drop of yellow oil of the same form as the sporidium, with the space between it and the cell wall occupied by a clear liquid, more fluid and less refractive, nearly colourless, or at times slightly roseate. As the membrane absorbed the water by which it was surrounded, the quantity of this clear liquid was augmented, and the rosy tint could be more easily distinguished. All the contents of the spore, which up to this time remained divided into two parts, presented altogether one aspect, only containing numerous granulations, nearly of equal size, completely filling it, and reaching the inner face of the sporic membrane.
After this time the sporidium augments in size very rapidly, becoming at times irregular, and sometimes even as much as from two to three times its original dimensions, then there appears at the surface, usually at one of the poles of the ellipse, a small prominence, with an extremely fine membrane, which does not appear to separate itself from that which surrounds the sporidium, and it is difficult to say whether it is a prolongation of the internal membrane going across the outside, or simply a prolongation caused by a continuation of tissue of an unique membrane. Sometimes there may be seen at the point where the primal filament issues from the sporidium a circular mark, which appears to indicate the rupture of the external membrane. From this time another change comes over the contents. We again find the yellow oily liquid, now occupying the external position, with some drops of colourless or roseate liquid in the centre, so that the oily liquid and the more limpid fluid interchange the positions which they occupied previous to the commencement of germination. Whether these two fluids have undergone any change in their constitution is difficult to determine, at all events the oily liquid appears to be less refractive and more granular, and it may be that it is a product of new formation, containing some of the elements of the primitive oily drop. Having regard to the delicate character of the membrane of the germinating filaments, De Seynes supposed that it might offer greater facility for the entrance of water by endosmose, and account for the rapid enlargement of the sporidia. By a series of experiments he became satisfied that this was the case to a considerable extent, but he adds:—“I cannot help supposing that a greater absorption of greasy matter in the cell which is the first product of germination raises an objection to an aqueous endosmose. One can also see in this experience a proof of the existence of two special membranes, and so suppose that the germinative cell is the continuation of the internal membrane, the external membrane alone being susceptible of absorbing the liquids, at least with a certain rapidity.”
Fig. 94.—Sporidium of Ascobolus germinating.
In other Discomycetes germination takes place in a similar manner. Boudier[P] narrates that in Ascobolus, when once the spore reaches a favourable place, if the circumstances are good, i.e., if the temperature is sufficiently high and the moisture sufficient, it will germinate. The time necessary for this purpose is variable, some hours sufficing for some species; those of A. viridis, for example, germinate in eight or ten hours, doubtless because, being terrestrial, it has in consequence less heat. The spore slightly augments in size, then opens, generally at one or other extremity, sometimes at two, or at any point on its surface, in order to pass the mycelium tubes. At first simple, without septa, and granular in the interior, above all at the extremity, these tubes, the rudiment of the mycelium, are not long in elongating, in branching, and later in having partitions. These filaments are always colourless, only the spore may be coloured, or not. Coemans has described them as giving rise to two kinds of conidia,[Q] the one having the form of Torula, when they give rise to continuous filaments, the other in the form of Penicillium, when they give birth to partitioned filaments. De Seynes could never obtain this result. Many times he had seen the Penicillium glaucum invade his sowings, but he feels confident that it had nothing to do with the Ascobolus. M. Woronin[R] has detailed some observations on the sexual phenomena which he has observed in Ascobolus and Peziza, and so far as the scolecite is concerned these have been confirmed by M. Boudier.
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.[S]