250 COLOCASIA BLIGHT. 



from the wall of the antheridium which, after traversing the cavity, 

 emerges on the opposite side. In some cultures a sort of secondary 

 thickening develops on the outside of the oogonium, the outline of 

 which becomes indistinct and granular or roughened (PL IV, Fig. 

 14). A similar condition has been observed in Phytophthora para- 

 sitica 1 and Ph. infestans 2 . 



The oogonia are subglobose and measure on an average 29\5m 

 in diameter (limits 24 to 35m). The oospores are almost exactly 

 spherical and average 23m in diameter (limits 20 to 28m). In these 

 measurements a few abnormally large oogonia, in which oospores 

 were not developed but which had normal antheridia, are omitted. 

 They measured up to 41m in diameter. So also in one or two tubes 

 some very small spores were found with oogonia only 19// and 

 oospores 15m in diameter. These were colourless and were pro- 

 bably degenerate forms. The antheridia vary considerably in 

 size, being from 7 to 13m in their longest diameter. 



Germination of the sexual spore has not been observed. 



IV. Inoculation experiments with Phytophthora 



Colocasia. 



Raciborski 3 tried to infect healthy leaves of Solanum tuberosum 

 and Nicotiana Tabacum with sporangia of the Phytophthora on 

 Colocasia, but without success. 



Sawada 4 successfully infected Taro (Colocasia antiquorum) 

 and " water-potato " (? Colocasia antiquorum var.) with sporangia 

 taken direct from a leaf and germinated in distilled water. He- 

 failed to infect similarly " Hasu-imo " (? Colocasia indica Hassk.) 

 and " Manshu-imo " (? Alocasia macrorhiza Schott.), though some 

 small non-spreading spots developed at the seat of inoculation. 



On its proper host Phytophthora Colocasice is highly infective. 

 Inoculations on the leaves with living active zoospores in distilled 



1 Dastur, J. F. On Phytophthora parasitica nov. spec, a new disease of the Castor oil 

 plant. Mem. Dept. of Agric. in India, Bot. Ser., V, No. 4, 1913. 



2 Clinton, G. P. Oospores of Potato blight. Conn. Exper. Sta. Report, 1909-10, p. 770. 



3 Raciborski, M. Parasitische Algen und Pilze Javas, I, 1900, p. 10. 



4 Sawada, K. Infection of Taro. Rep. from Special Reports of the Formosan Agric. 

 Exper. Sta., II, 1911, p. 7 of the reprint, 



