244 COLOCASIA BLIGHT. 



absence of oospores, being noticed on the three more satisfactory 

 media, mentioned above. 



The mycelium covers the surface of the medium rather slowly 

 and forms a white aerial growth, on which are found mature spo- 

 rangia in about a week or ten clays at temperatures of 15 to 20°C. 

 The hyphse of the aerial mycelium are long, sparingly branched, 

 about 4 to 7m in breadth and not varying abruptly in diameter 

 (PL III, Fig. 4). Septa are frequent, but instead of being formed. 

 as in the higher fungi, regularly from behind forward at a short 

 distance from the growing apex of the hypha, they are laid down 

 irregularly throughout its length, dividing it into compartments 

 which may contain living protoplasm or be empty of all contents. 

 Sometimes a new branch may arise from below a septum, as shown 

 in PI. Ill, Fig. 4a. The septation increases as the culture ages 

 and in old or badly nourished cultures is very free. In addition 

 to complete partitions, isolated nodules, spines and plates of 

 cellulose are laid down very commonly on the inside of the hypha 1 

 wall. Some of these may be seen in PI. Ill, Fig. 8a. It naturally 

 suggests itself that such cases as these represent early or arrested 

 stages in the formation of complete septa, the process being then of 

 the type known as Spirogyra or Allomyces. In several cases, however, 

 the septum appears first as a thin plate, such as that shown in c of the 

 same figure, and it has not been possible to decide whether this 

 is preceded by a stage of the type figured in a. The mature septum 

 usually becomes much thickened, the most common form showing a 

 conical thickening, which in septa dividing full from empty portions 

 of a hypha is always directed to the full side (Fig. 86). Sometimes 

 there is a corresponding depression on the opposite side and in the 

 earlier stages a pore has been distinctly seen in the centre of the 

 septum. The conical thickening marks the subsequent closure 

 of this pore. Septa often develop at the origin of a lateral branch 

 (Fig. Sd). All the septa, as well as the hyphal walls and the 

 sporangia, give typical cellulose reactions. 



The mycelium which creeps on the surface of the medium, 

 where a densely felted layer is often formed, is more freely branched 



