620 COMPARATIVE MORPHOLOGY OF FUNGI 



zygogamous series, but the details in both series differ character- 

 istically. We will review only two points, important for the course of 

 the discussion. 



A first point lies in the striving for a uninucleate condition of the 

 sexual cells, by which the development of uninucleate gametes to mul- 

 tinucleate (polyenergid) gametangia (so-called coenogametes) is again 

 paralyzed. In the Oomycetes this tendency expresses itself next (in the 

 Saprolegniaceae p. 68) in the female gametangia by the degeneration of a 

 portion of the nuclei before and during their activation as sexual nuclei, 

 wherefore the content of the gametangia round up about the remaining, 

 privileged sexual nuclei, forming egg cells. Thus the virtually female 

 gametes within the coenocytic gametangia recover functionally their 

 earlier individuality; they no longer swarm but each secures for itself 

 a male nucleus by means of a special branch of the reproductive sac. In 

 the Peronosporaceae, the differentiation between the functional and 

 supernumerary female energids (or sexual nuclei) extends to the proto- 

 plasm, and separates it as gonoplasm which is used for the fundaments 

 of the single eggs, and periplasm which serves only vegetative purposes. 

 Thereupon selection goes still further and moves all but one of the privi- 

 leged sexual nuclei from the coenocytic egg cell into the periplasm, where 

 they function vegetatively (pp. 80-87). In the Zygomycetes this tend- 

 ency expresses itself by a lessening of the number of active sexual nuclei 

 so that in Endogone lactifiua (p. 115) all but the one functional nucleus at 

 the base of the copulation branch withdraw and are abjointed from the 

 gametangium proper. With the privileging of a single sexual nucleus, 

 the oogamous and zygogamous series have again reached the stage of 

 the lowest fungi as regards the effect of their sexual organs : again a single 

 uninucleate zygote, arises as the product of the sexual act; only this uni- 

 nucleate zygote, which in Olpidium and Monoblepharis was the prod- 

 uct of two daughter cells of the gametangia, is now the product of two 

 gametangia themselves : as in the retrogression of the sporangia to conidia, 

 here too the whole organ assumes the function of its part. 



A second point in the development of gametangia lies in the retarda- 

 tion of caryogamy; this no longer immediately follows on the completion 

 of the sexual act, plasmogamy, but it may be postponed for months in 

 both the oogamous and zygogamous series (pp. 84, 112); in certain forms, 

 as in Basidiobolus (p. 118), its initiation is dependent upon environment, 

 and is hastened by drying out and retarded by liberal nourishment. 

 This retardation of caryogamy is accompanied in the higher forms by a 

 shifting in position : the zygote continues its growth before the occurrence 

 of caryogamy in the outgrowths of the zygotes {e.g., in Endogone, p. 115). 

 Similarly, meiosis may be retarded and shifted, so that it occurs only in 

 the sporangia which arise on the germination of the zygotes {e.g., in the 

 "germ sporangia" of Phy corny ces, (p. 112). 



