Berkeley, “Introduction to Crypt. Bot.” p. 266.
VI.
THE SPORE AND ITS DISSEMINATION.
A work of this character would hardly be deemed complete without some reference to the above subject, which has moreover a relation to some of the questions discussed, and particularly of spore diffusion in the atmosphere. The largest spore is microscopic, and the smallest known scarcely visible under a magnifying power of 360 diameters. Taking into account the large number of species of fungi, probably scarcely less numerous than all the flowering plants, and the immense number of spores which some of the individuals produce, they must be exceedingly plentiful and widely diffused, though from their minuteness not easy to be discerned. It has been attempted to estimate the number of spores which might be produced by one single plant of Lycoperdon, but the number so far exceeds that which the mind is accustomed to contemplate that it seems scarcely possible to realize their profusion. Recent microscopic examinations of the common atmosphere[A] show the large quantity of spores that are continually suspended. In these investigations it was found that spores and similar cells were of constant occurrence, and were generally present in considerable numbers. That the majority of the cells were living, and ready to undergo development on meeting with suitable conditions, was very manifest, as in those cases in which preparations were retained under observation for any length of time, germination rapidly took place in many of the cells. In few instances did any development take place, beyond the formation of networks of mycelium, or masses of toruloid cells, but, in one or two, distinct sporules were developed on the filaments arising from some of the larger septate spores; and in a few others, Penicillium and Aspergillus produced their characteristic heads of fructification. With regard to the precise nature of the spores, and other cells present in various instances, little can be said, as, unless their development were to be carefully followed out through all its stages, it is impossible to refer them to their correct species or even genera. The greater number of them are apparently referable to the old orders of fungi, Sphæronemei, Melanconei, Torulacei, Dematiei and Mucedines, while some probably belonged to the Pucciniæi and Cæomacei.
Hence it is demonstrated that a large number of the spores of fungi are constantly present in the atmosphere, which is confirmed by the fact that whenever a suitable pabulum is exposed it is taken possession of by floating spores, and soon converted into a forest of fungoid vegetation. It is admitted that the spores of such common moulds as Aspergillus and Penicillium are so widely diffused, that it is almost impossible to exclude them from closed vessels, or the most carefully guarded preparations. Special contrivances for the dispersion of the spores in the different groups follow a few general types, and it is only rarely that we meet with any method that is confined only to a species or genus. Some of the more significant forms of spores may be illustrated, with their modes of dissemination.
Basidiospores is a term which we may employ here to designate all spores borne at the tips of such supports as are found in the Hymenomycetes and Gasteromycetes, to which the name of basidia has been given. In fact, under this section we may include all the spores of those two orders, although we may be ignorant of the precise mode in which the fruit of most of the Myxogastres is developed. Guarding ourselves at the outset against any misinterpretation as to the use of this term, which, in fact, we employ simply to designate the fruit of Hymenomycetes, we may have excuse in our desire to limit special terms as much as possible. In the Agaricini the spores are plentiful, and are distributed over the hymenium or gill plates, the surface of which is studded with basidia, each of which normally terminates with four short, erect, delicate, thread-like processes, each of which is surmounted by a spore. These spores are colourless or coloured, and it is upon this fact that primary divisions in the genus Agaricus are based, inasmuch as colour in the spores appears to be a permanent feature. In white-spored species the spores are white in all the individuals, not mutable as the colour of the pileus, or the corolla in phanerogamic plants. So also with the pink spored, rusty spored, black spored, and others. This may serve to explain why colour, which is so little relied upon in classification amongst the higher plants, should be introduced as an element of classification in one of the largest genera of fungi.
Fig. 45.—Spores of (a) Agaricus mucidus; (b) Agaricus vaginatus; (c) Agaricus pascuus; (d) Agaricus nidorosus; (e) Agaricus campestris. (Smith.)
