•J04 PHYTOPHTflORA PARASITICA. 



portions of the culture tube contain a lot of them in all stages 

 of development, while in other portions there is no trace of 

 them. 



Ph. parasitica oospores have been found in French-bean juice 

 agar and oat juice agar but they have only been obtained when 

 these media were inoculated from cultures growing on a different 

 medium. 



Clinton has found it difficult to decide whether the oogonial 

 thread '' did not actually penetrate the antheridium and grow 

 through it," but " the optical effect was frequently that of an internal 

 thread." I have not found a single case in which the oogonial 

 origin was not within the antheridium. The microphotographs 

 bear independent evidence to the unique mode of development of 

 the oogonium. One of them (Plate VII, Fig. 1) shows the 

 oogonial thread arising as an ingrowth within the antheridium. 

 Another (Plate VII, Fig. 5) shows a roughly manipulated oospore. 

 At the apex of the antheridium the elliptical opening made by the 

 oogonial thread was distinctly visible. Within the antheridium is 

 seen the passage made by the oogonial thread in the course of its 

 upward progress. Plate VI, Fig. 16, shows an unfertilised oogonium 

 which through rough handling got a little separated from its 

 antheridium. This figure clearly illustrates the exact origin of the 

 oogonium. 



It is a matter of common observation that when a hypha 

 penetrates its host cell at right angles to it, under the microscope the 

 penetrating end of the hypha, observed vertically, appears as a con- 

 tinuous chain of rings lying within the cell when the fine adjustment 

 of the microscope is being used. The same phenomenon is observed 

 in the antheridium which is being pierced by an oogonial hypha 

 (Plate VI, Fig. 1). When the oogonium and antheridium are on 

 the same hypha the oogonial stalk broadens out at the place of its 

 origin at the base of the antheridium. All these observations leave 

 no doubt as to the oogonium arising from within the antheri- 

 dium. 



