248 COLOCASIA BLIGHT. 



never on a special lateral "stalk, the absence of an oogonial wall 

 distinct from that of the spore, the absence of the antheridium, 

 which is large and persistent in the sexual stage, the frequent 

 occurrence in the superficial mycelium, whereas oospores are onlv 

 produced buried in the medium and the variation in size in the 

 same culture, which is much greater than with the sexual spores. 



Their germination has not been followed. That they do not 

 form zoospores is probable from the absence of a papilla and the 

 fact that empty cases were not seen. They seemed to germinate 

 bv putting out a germ-tube in some cases but it was difficult to be 

 certain that these were not intercalar chlamydospores and the 

 supposed germ-tube merely the continuation of the stalk. 



Oospores have been produced in considerable numbers in some 

 of the cultures. They have been found hitherto only in French- 

 bean agar, and in cultures which all belonged to the same strain, 

 i.e., arose from the same original parent. They continued to 

 develop in sub-cultures carried on over a period of six months and 

 equally whether grown for several generations on this medium or 

 when grown for one or more generations on other media such as 

 corn meal or prune-juice agar and again transferred to French- 

 bean agar. They were produced at laboratory temperatures during 

 the coldest and hottest parts of the year, in a range of temperature 

 from 15° to 30°C. daily mean. 



The oogonia are found only in the entirely submerged myce- 

 lium, generally in a layer about one-eighth of an inch from the 

 surface and are at once recognisable by the prominent and charac- 

 teristically shaped antheridium (PL IV), which persists for months. 

 Their development presents points of great interest, which were 

 detected in this species almost simultaneously with those of the 

 oogonia of Phytophthora parasitica Dastur, with which they agree 

 in their main features. The antheridium is first formed as a club- 

 shaped swelling at the end or near the end of a hypha, possibly 

 sometimes also by direct lateral swelling in the course of the latter. 

 When mature it is cut off by a distinct septum to form the male 

 cell. To it now grows a branch, usually a lateral outgrowth from 



