416 COMPARATIVE MORPHOLOGY OF FUNGI 



basidia. This expression, germination, shows as nothing else, how far 

 these two structures have become separated from each other in time 

 and how much we perceive them as two organs in our use of terms, in 

 spite of their original unity. Finally the sclerobasidium is set free from 

 its hypha, becomes a spore and fills, in addition to its function as resting 

 cell, also the function of propagation in some Uredinales (teliospore, 

 Fig. 389) and also in the Ustilaginales (smutspore, chlamydospore, Fig. 

 399). Here, internally as well as externally, it has nothing in common 

 with the basidium and its original connection can only be determined 

 by phylogenetic comparison. 



After this digression, let us return to the basidium at the point where 

 we left it on page 414, after the maturing of the spores. Beside the 

 narrow isthmus in the sterigmata next the lower end of the spores, a 

 small drop of liquid appears at a definite moment a few seconds before 

 the discharge of the spores; this rapidly reaches its maximum size, 

 approximately half the diameter of the spore; if the secretion of the drop 

 of liquid is suppressed or if it is abnormally large, the discharge of the 

 spore is also suppressed. The isthmus gelifies more or is ruptured, and 

 the spore, together with the drop, is suddenly discharged for a distance of 

 0.1 to 0.2 mm., i.e., ten to twenty times its own length and the sterigma 

 collapses. Although the mechanism of discharge is still vague, in some 

 cases it is certain that the separation of the spores is completed actively 

 (as with the asci) by a forcible discharge ; the efficiency of this discharge 

 is much smaller, however, than that in the Ascomycetes and is never 

 sufficient (e.g. in resupinate forms, if the hymenium were on the upper 

 surface) to shoot the spores over the edge of the crust or to shoot them 

 up high enough so that they may be taken up in the currents of air and 

 be carried off. It is, consequently, apparent that the tendency of the 

 Basidiomycetes to bear their hymenia on the under side of the fructifi- 

 cations where free fall aids dissemination, is connected with this small 

 range. With the average rate of fall of 1 to 5 mm. per second, the spores 

 of a terrestrial fungus reach the surface of the earth in approximately 

 one minute. This time, under normal conditions, would suffice to allow 

 them to be carried off by currents of air. It is even possible that the 

 enormous masses of nourishment of the fructification, regarded teleo- 

 logically, are used in spore dissemination. Falck has demonstrated that 

 these fructifications always have a higher temperature than their sur- 

 roundings and that this warmth suffices, at least in limited spaces (e.g., 

 under leaves, etc.), to create small currents of air which carry the spores 

 by convection. 



This small range of a few tenths of millimeters explains why the 

 pezizoid fructifications of the Basidiomycetes (with the hymenium on 

 the inner side) are so seldom formed and why, if they do occur, they are 

 inverted, i.e., with the cavity of the cup beneath. The spores could not 



