﻿1903] OOGENESIS IN SAPROLEGNIA 337 



are left the most conspicuous of the Phycomycetes in three 

 orders, that agree primarily in having either typical coenog- 

 ametcs (Mucorales) or sexual organs probably derived from 

 coenogametes (^Peronosporales and Saprolegnialcs). 



These three orders, however, can only be related to one 

 another through a common ancestry whose sexual organs were 

 coenogametes. The Mucorales illustrate most completely the 

 primitive coenogamete, and for this reason in part may be con- 

 sidered rather the lowest of the three groups. In the Perono- 

 sporales we have an ascending series from forms such as Albugo 

 Bliti and A. Portulacae with true coenogametes, although more 

 highly specialized than those of the molds, to the conditions in 

 Albugo ca7idida^ Peronospora, and Pj^thium. This advance is 

 evidently such an evolution as would provide a single uninucleate 

 ^gg with the richest supply of food and best protective walls 

 possible. In the Saprolegnialcs the evolutionary trend is similar 

 in that a great many potential gamete nuclei are sacrificed to 

 give a uninucleate ^%%, but we are not yet prepared to trace 

 exactly the steps in the origin of this oogonium. However, the 

 probabilities are that it, too, has come from a coenogamete, and 

 that the segmentation of this protoplasm to form many eggs 

 does not imply a derivation from heterogamous ancestry, but 

 special peculiarities associated perhaps with the presence of 

 several coenocentra. Oogenesis in Saprolegnia certainl}^ indi- 

 cates an ancestry with coenogametes. The Mucorales, Perono- 

 sporales, and Saprolegnialcs then probably come from a somewhat 

 similar ancestry with coenogametes, which necessitates their 

 derivation from isogamous algae at about such a level as is 

 illustrated today by Cladophora and forms of the isogamous 

 Siphonales. 



We do not propose to discuss the phylogeny of the Ascomy- 

 cetes further than to present its problem with respect to the 

 coenogametes. The difficulty of relating the diverse sexual 

 organs represented by Sphaerotheca, Pyronema, the lichens, and 

 the Laboulbeniaceae has led to suggestions that the Ascomycetes 

 are polyphyletic. But this view has many objections in the 

 essential unity of the ascocarps and general rhythm of the life- 



