238 COLOCASIA BLIGHT. 



a sterile knife a slab from the margin of a rotting patch and dropping 

 it into pure water in a sterile flask. In some cases a copious exter- 

 'nal growth was obtained by this treatment and mature sporangia 

 were formed on the third day. The fungus maintains its vitality 

 for a considerable time in the conn. PI. Ill, Fig. 14 shows a 

 hypha obtained by incubating a corm about a month after it was 

 harvested and some three months after the disease had ceased to be 

 active. It is probable too that corms kept under conditions which 

 permit of moisture to accumulate, develop aerial hyphse in store 

 and infect their neighbours. There is no reason to doubt that the 

 parasite can persist from one season to another in the corms and, 

 as in the allied potato blight, infection of the new crop possibly 

 comes in part from these diseased tubers. Resting spores, whether 

 sexually produced oospores or the thick walled reproductive bodies 

 known as chlamydospores, have not been found in nature, though 

 they have been obtained in artificial cultures. 



On the leaf the sporangia are borne on short stalks as shown 

 in PI. II, Fig. 1. They are terminal and single but sometimes the 

 stalk continues to grow by a branch arising below the sporangium, 

 the latter being pushed to one side and a new sporangium being 

 formed at the tip of the branch (PI. Ill, Fig. 15). The sporangiophore 

 narrows towards the apex to an extremely slender thread, some- 

 times not exceeding 1\5m in diameter, and the sporangium falls 

 with a part of this narrow stalk attached to its base. The fructi- 

 fying hyphse emerge, as shown in the figure, not only through 

 stomata (the usual mode of emergence in Peronosforacea) but also 

 between or through the epidermal cells. They rarely exceed 50/w 

 in length and, excepting in the rather infrequent case of more 

 than one sporangium being borne, they are unbranched. 



The sporangia are colourless, elliptical or pear-shaped, some- 

 times curved and less regular in shape than is the case with most 

 species of Phytophthora. They are often very large, measuring 

 when formed on the leaf from 38 to 60 by 18 to 26^ in diameter but 

 varying within wider limits in culture. Sawada has. observed 

 sporangia up to 11 4m in length on the leaf, but in India they rarely 



