﻿3^6 BOTANICAL GAZETTE [may 



under the topic *'Phylogeny of the Phycomycetes and Ascomy- 

 cetes." It is important that we emphasize now the evolutionary 

 process brought out by Stevens's work on the four species of 

 Albugo, and extend the results of that study to the Penorospo- 

 rales as a whole. Accordingly we have good reason to believe 

 that the uninucleate eggs of Albugo Candida, Peronospora, and 



Pythium have not been derived from the eggs of algal ancestry, 



but from coenogametes which passed through the stage illus- 

 trated by Albugo Bliti, and came from much simpler conditions, 

 probably resembling in many respects the coenogametes of the 

 molds and Pyronema. 



An origin of the simplest types of coenogametes (molds and 

 Pyronema) from gametangia of algae presents certain difficulties 

 that should be discussed. The process would involve a change 

 in the activities of a structure from one where the nuclei show 

 a considerable degree of independence to one in which the nuclei 

 cooperate in a coenocytic cell that acts as a unit. An evolu- 

 tionary process comparable to the above must have taken place 

 with the development of the multinucleate zoospore of Vaucheria, 

 if its nuclei stand for the numerous zoospores generally formed 

 in the terminal sporangia of the Siphonales. And a similar evo- 

 lution, as has been mentioned before, is shown in the develop- 

 ment among the Peronosporales of conidia (which germinate by 

 tubes) from sporangia (conidia) that form zoospores. Such 

 conidia and the zoospores of Vaucheria are not considered the 

 equivalent of tissues, but units in their physiological behavior, 

 just like uninucleate spores. 



Similarly, the coenogamete is not the equivalent of a tissue, 

 and must not be considered as made up of independent gametes 

 associated together because their cytoplasm is fused into a com- 

 mon mass. It exhibits the same sort of individuality as any 

 coenocytic cell or. structure. We no longer draw sharp lines 

 between uninucleate and multinucleate cells, for we realize that 

 the transformation of the first into the second is a very simple 

 matter, and that the unity of the coenocyte is not disturbed by its 

 having several or many nuclei, for these do not occupy fixed 

 positions in the cell but wander with the varying movements of the 



