﻿1903] OOGENESIS IN SAPROLEGNIA 321 



what have they been derived among the algae ? It will be agreed 

 that the Mucorales, Albugo Bliti, and Pyronema illustrate com- 

 pletely the conception of a coenogamete. It is a part of our 

 problem to determine the relation of these conditions to the 

 sexual organs in other species of Albugo, and in Peronospora, 

 Pythium, and the Saprolegniales. There may be some hesitancy 

 in following the series of homologies that the WTitcr will pro- 

 pose, and the evolutionary history to be suggested; but he can 

 see only two possibilities, of which one is so obscure that it 

 seems almost impossible in the light of our present knowledge, 

 incomplete as it is. 



The most important structures in the coenogamete are the 

 nuclei, and there can be hardly any question that they indi- 

 vidually stand for energids, which among the algae are independ- 

 ent uninucleate gametes. Stevens's (1899) term ** compound 

 oosphere " expressed very well this conception of the conditions 

 in Albugo Bliti, It was employed when this form was the only 

 type known presenting the structure implied by the phrase, and 

 these conditions might have been purely exceptional. But we 

 now know from later studies of Stevens (1901) that other spe- 

 cies of Albugo, A. Portiilacac, A. Tragopogonis, and A. Candida^ 

 have phases of ontogeny identical with the essential periods of 

 oogenesis in A, Bliti, and may be brought into very intimate rela- 

 tion to the latter species. We also know that the coenogamete 

 is not restricted to the Peronosporales, but is characteristic of 

 the Mucorales, and is found also among the Ascomycetes. It is 

 not likely that we shall retain the phrase *' compound oosphere/' 

 for a broader conception will probably take its place, but a pur- 

 pose has been served and a field opened to investigation that 

 was quite undreamed of by the earlier investigators of the Phy- 

 comycetes. 



The nuclei of coenogametes are homologous with nuclei in a 

 gametangium destined to develop independent sexual cells. 

 Hartog's (1891) conception of the nuclei in the periplasm of 

 Peronospora as representing degenerate gametes has been com- 

 pletely justified, and there are very good reasons for believing 

 that the nuclear divisions in the oog^onium and antheridium of 



