PERONOSPO RALES 1017 



of the protoplasm is discernible, and after a few seconds slight con- 

 tractions in certain regions lend a lumpy irregular appearance to the 

 mass (Fig. 83 E). Faint peripheral lines of cleavage, which demarcate 

 irregularly polygonal areas, soon become visible in the now slightly 

 more contracted contents. About three minutes after discharge a 

 rocking movement of the mass is noticeable. The lines of cleavage have 

 by this time definitely delimited the spore initials (Fig. 83 F), which 

 exhibit a slight individual movement approximately six minutes after 

 the discharge. Short hyaline flagella may now be definitely seen around 

 the periphery. The movement of the spore initials gradually becomes 

 more pronounced, assuming a twisting or writhing character as the 

 spore masses slowly become separated from one another. At about 

 eight minutes after discharge a small vacuole becomes visible in each; 

 the previously short hyaline flagella have increased in length by this 

 time and appear as flexible lashes (Fig. 83 G). Three minutes later the 

 spores have become nearly mature individuals. They still continue, 

 however, to oscillate somewhat until they are perfectly formed (Fig. 83 

 H). About fourteen minutes after egress this motion is gradually super- 

 seded by a frenzied milling around of the zoospores within the con- 

 fines of the vesicle. Finally the vesicle is ruptured, usually in the upper 

 part, by one or more zoospores, and the mature swarmers escape. 

 The vesicle is ultimately dissolved into the surrounding medium. 



In the lobulate and sphaerosporangial species of Pythium the sequence 

 of zoospore formation in the vesicle is essentially like that just described. 



The zoospores of Phytophthora are delimited within the sporangium 

 and upon emergence may or may not be surrounded by a quickly 

 evanescent vesicle. In Phytophthora, as in Pythiogeton and certain of the 

 sphaerosporangial species of Pythium, formation of new sporangia 

 occurs by internal proliferation (Figs. 87 A, p. 1032; 89 A, F, p. 1055; 

 90 B, D, G, p. 1059). 



The zoospore of all members of the Pythiaceae is of the laterally 

 biflagellate secondary type. It is usually capable of repeated emergence 

 (Fig. 86 D, p. 1030). The flagellar structure is like that of the 

 "secondary" zoospore of Saprolegnia (p. 10). 



