PYTHIUM 243 



siderable bulk of fresh water : examine the culture at intervals 

 under a low power. Some of the conidia will be seen to 

 germinate by the formation of tubular hyphae similar to those 

 which produced them. 



VI. Continue at intervals the observation of those cultures 

 which have already produced conidia : the formation of the 

 sexual organs will frequently be seen to succeed that of the 

 conidia. 



a. The oogonium resembles at first the conidium in being 

 spherical, and about of equal size with it, and is partitioned off 

 by a septum ; a central spherical mass of protoplasm (the 

 ovum) is to be recognized. 



b. The antheridium arises as a branch, either from the same 

 filament as the oogonium, or from another : its apex is cut off 

 by a septum, and it comes in close contact with the oogonium : 

 a cylindrical process from it passes through the wall of the 

 oogonium, and gains access to the ovum. 



c. In more mature specimens the oogonium contains a single 

 round, distinctly walled cell (the oospore), which lies freely 

 within it. 



Observations may also be made on the Potato Fungus (Phyto- 

 phthora infestans) the mycelium of which permeates the tissues 

 of the Potato plant, while its branched conidiophores project 

 through the stomata. 



