REVIEW OF FUNGOUS CLASSIFICATION 627 



Besides in the Basidiomycetes, manifold morphological modifications 

 occur in the pseudogamous sexual process; in parasitic forms (the Uredin- 

 ales and some Ustilaginales) the plasmogamy is localized mainly in hyphal 

 knots from which subsequently arise definite spore forms (aeciospores, 

 p. 555; urediniospores, p. 564; and teliospores, p. 569. On the other 

 hand, it may become entirely labile and, as sexual maturity apparently 

 appears earlier and earlier, they move to the germ mycelia of the basidio- 

 spores, by increasing shortening of the haplont (Peniophora Sambuci, 

 p. 400), and finally to the basidiospores (Tilletia Tritici, p. 596). Thus 

 plasmogamy has become shifting, perittogamous. It seems as if it no 

 longer mattered to the Basidiomycetes, as to the fungi in general, when, 

 where and how plasmogamy occurs, so long as the double chromosome 

 number is retained; the sporophytes are capable of greater morphological 

 differentiation, however, than the gametophytes. Finally, also the 

 indirect copulation of two basidiospores (which in any case is only a 

 formality) disappears and the nucleus which has migrated into basidio- 

 spore (possibly like the original homothallic forms) divides directly into 

 two daughter nuclei which henceforth behave as a dicaryon (Gastero- 

 mycetous type, p. 397). In this last stage of sexual degeneration, no 

 foreign nuclear material is introduced from without and cytological 

 development is wholly internal and intracellular (endocaryogamy in 

 the stricter sense, in contrast to exocaryogamy). The Corticium 

 bombycinum type no longer has plasmogamy but only caryogamy. The 

 importance of this endocaryogamy, however, lies in the fact that it makes 

 possible for the individuals in question synapsis and meiosis and conse- 

 quently a new combination of their chromosomes, a relationship which, 

 because it must lead to a cessation of phylogenetic development, undoubt- 

 edly suffices for the individual but not for the species. Hence the step 

 to complete apogamy is short. 



With this shifting of plasmogamy in space and time, there goes a 

 degeneration as regards its content. Just as plasmogamy disappears 

 and finally takes place only as an episodical occurrence between two 

 vegetative hyphae somewhere outside in the mycelium, so also its prod- 

 ucts lose their specific character: the physiologically dependent, dicary- 

 otic, ascogenous hyphae have become a secondary Basidiomycetous 

 mycelium (p. 401), which henceforth, like any vegetative hyphae, is cap- 

 able of independent existence, especially food intake (p. 405) and propaga- 

 tion by independent forms (p. 407) and, after its formation, develops with 

 such complete habitual correspondence with the original haploid hyphae 

 that, except for eventual clamp formation, its diploid character can only 

 be definitely determined by cytological investigation. The difference 

 between the Euascomycetes and Basidiomycetes in respect to their 

 dicaryotic generation, is thus only quantitative; while in the Euascomy- 

 cetes the haplont and diplont were two phases of a cycle, the second of 



