REVIEW OF FUNGOUS CLASSIFICATION 619 



the sporangiospores of certain Zygomycetes) is retarded and the sporangia 

 germinate with germ tubes before this individualization has begun; 

 consequently they gradually assume the function of their daughter cells, 

 especially that of propagation, and gradually separate as a whole from the 

 mother plant and become conidia (p. 30). In the Oomycetes, this 

 reduction of the sporangium to a single spore occurs exclusively by an 

 inhibition of zoospore formation; thus it has remained an entirely internal 

 process which has not had direct reaction on the form and size of spor- 

 angia (pp. 74-78). In the Zygomycetes discussed here (pp. 104-108), 

 however, the primary consideration is not in the inhibition of the 

 formation of sporangiospores whose individuality is retained, but in the 

 degeneration of sporangia; to a certain degree the pressure comes from 

 the outside and with the decrease in size of sporangia leads also to a 

 decrease in number of sporangiospores ; in place of many-spored sporangia, 

 there arises a single conidium. Thus in the oogamous and zygogamous 

 series the releasing forces have been of a different nature but the effect 

 has been the same: the functions of the daughter cells are gradually 

 assumed by the mother cells ; this is the indication of degeneration : totum 

 pro parte. Besides in the Choanephora-Piptocephalis series of the Zygo- 

 mycetes (pp. 101-105), we have an example of how, by retardation of 

 spore formation, the spores can be formed exogenously instead of endog- 

 enously and how, consequently, a form of fructification can divide into two 

 types whose genetic connection may only be determined experimentally. 



B. Gametangia. — As in the sporangia, so also in the gametangia, 

 which have apparently arisen from sporangia, there is no individualiza- 

 tion of single energids and instead of two true uninucleate gametes, 

 so-called merogamy, there appears first the copulation of (coenocytic) 

 gametangia themselves (p. 59 et seq.). As the sporangia, so also the 

 gametangia assume the functions of their daughter cells; again totum 

 pro parte instead of pars pro toto, the indication of genetic degeneration. 



With this deuterogamous substitute of the original merogamy 

 begins that crisis of sexuality that may be traced through the whole 

 system of fungi. At first it would seem as if these membrane-surrounded 

 gametangia offered a definite biological advantage over the naked gametes, 

 for it is no longer left to chance whether two gametes find each other, but 

 the gametangia themselves provide that the nuclei of both parents should 

 reach each other and become sexually active. Thus fewer sexual cells are 

 formed but they are better developed. Furthermore, this development 

 from merogamy to gametangial copulation (parallel with the development 

 of imperfect forms from hydrochory to anemochory) has made possible 

 or facilitated the transition of fungi from aquatic to terrestrial habitats and 

 to parasitism in the interior of other plants (p. 73 et seq.). Thus at 

 first the gametangia functioning as sexual cells undoubtedly show a 

 further development; this may be observed both in the oogamous and 



