Fungi: Their Nature and Uses

by M. C. Cooke

Sporangia are produced in the Physomycetes usually on the tips or branches of delicate threads, and these when mature dehisce and set free the minute sporidia. These are so small and uniform in their character that they require but a passing mention. The method of diffusion agrees much with that of the Mucedines, the walls of the sporangia being usually so thin and delicate as to be easily ruptured. Other modes of fructification prevail in some species by the production of cysts, which are the result of conjugation of the threads. These bodies are for the most part furnished with thicker and more resistant walls, and the diffusion of their contents will be regulated by other circumstances than those which influence the dispersion of the minute sporidia from the terminal cysts. Probably they are more perennial in their character, and are assimilated more to the oogonia of Cystopus and Peronospora, being rather of the nature of resting spores, inasmuch as the same threads usually bear the terminal fruits.

Fig. 64.—Sporidium of Genea verrucosa.

Fig. 65.—Alveolate sporidium of Tuber.

Thecaspores is a term which may be applied generally to all sporidia produced in asci, but these are in turn so innumerable and variable that it will be necessary to treat of some of the groups individually. The Thecaspores, for instance, of the Tuberacei offer several features whereby they may be distinguished from other thecaspores. The asci in which these sporidia are generated mostly partake of a broadly saccate, ovate form. The number of sporidia contained in an individual ascus is usually less than in the majority of the Ascomycetes, and the sporidia approximate more nearly to the globose form. Usually, also, they are comparatively large. Many have been figured by Corda[C] and Tulasne.[D] Three types of spores may be said to prevail in the Tuberacei: the smooth spored, the warted or spinulose, and the areolate. The first of these may be represented by the Stephensia bombycina, in which the globose sporidia are quite smooth and colourless. The warted sporidia may be observed in Genea verrucosa, the spinulose in Tuber nitidum, and the areolate are present in Tuber æstivum and Tuber excavatum, in which the epispore is divided into polygonal alveoli, bounded by thin, membranaceous, prominent partitions. This form of sporidium is very beautiful. In all no special provision is made for the dissemination of the sporidia, as, from their subterranean habit, none would be available save the ultimate dissolution of the external integuments. As they are greedily devoured by several animals, it is possible that they may be dispersed through the excrements.

In the Perisporiacei the perithecium has no proper orifice, or ostiolum, for the discharge of the mature sporidia, which are usually small, and are disseminated by the irregular rupture of the somewhat fragile conceptacles. The asci are usually more or less saccate, and the sporidia approximate to a globose form. The asci are often very diffluent. In Perisporium vulgare the ovate brown sporidia are at first, and for some time, attached together in fours in a concatenate or beaded manner. In some species of Erysiphei the conceptacle encloses but a single sporangium, in others several, which are attached together at the base. In some species the sporangia contain two, in others four, in others eight, and in others numerous sporidia. In Chætomium the asci are cylindrical, and in most cases the coloured sporidia are lemon-shaped. When the conceptacles are fully matured, it is commonly the case that the asci are absorbed and the sporidia are free in the interior of the conceptacles.

Fig. 66.—Asci, sporidia, and paraphyses of Ascobolus (Boudier).