JEHANGTR FARDUNJI DASTUR 239 



in which it is growing, as in Phytophthoix on castor ; but very often on the 

 same medium smooth and lough-walled oospores have been produced, the 

 development of secondary thickening depending upon local conditions. In 

 French bean juice agar the oogonium is very slightly yellow tinted, almost 

 hyaline ; in Oat juice agar and Quaker-Oat agar it is honey-coloured ; in the 

 latter medium of a lighter colour than in the former. 



The size of the oospore,, unlike that of the PhytojjhtJw/a on castor, is also 

 influenced by the medium in which it is grown. In French bean juice agar it 

 varies from U — IS/j. in diameter, extreme measurements being U/j. and 20/* 

 and the average of 97 measurements being loSfi ; in Oat juice agar and in 

 Quaker-Oat agar from 16 — 21/^ in diameter, extreme measurements being 

 15/^ and 23/^^ and the average of 57 measurements being 18-4/u; the size 

 of the oospores on these last two media closely agrees with that of oospores 

 of the castor fungus. Generally the wall of the oospore is not very thick-, but 

 it seems that it is inversely propoitional to the thickness of the surrounding 

 oogonial wall. In French bean juice agai, it is slightly thicker than in Oat 

 juice agar oi Quaker-Oat agar. The oospore is hyaUne in colour. 



Attempts were made to germinate oospores in tap water and sterihzed 

 water taken from wayside pools but they failed, while a few of the many 

 oospores from Oat juice agar sown in wet earth showed attempts at germina- 

 tion. It appears that the germination is preceded by the disappearance of the 

 oil globule or globules and by the fine protoplasmic contents of the oospores 

 turning coarser. The germination is accompanied by the complete or partial 

 dissolution of the oospore wall (Figs. 11 to 14). A\Tien the oospore is just 

 beginning to germinate its wall shows at times a zig-zag outline due to its 

 unequal dissolution. (Fig. 12), as observed by Pethybridge^ in the germinating 

 oospores of Ph. enjihroseptica Pethyb. In one case the germ-tube had grown 

 into a long branched hypha, the end of one of the branches being swollen 

 as if it was going to form a sporangium (Fig. 14) ; but further growth did not 

 take place as the hypha became empty of its contents. From the few cases 

 observed it seems that the colour of the oogonium of the germinating oospore 

 groNNing on Oat juice agar becomes lighter. Two oospores in an Oat juice 

 agar tube were fomid to have produced short germ-tubes, one each. In 

 both these cases the oospore wall had completely dissolved, and the oogonium 

 was 23aitly empty. In one a thin layer of protoplasm was lining the inside 

 of the oogonial wall. No oil globules were found within the two germinating 

 oospores and the contents were coarsely granular. As far as could be judged 



' tethybridge, G. H. Further observations on Ph. erythroseptica Pethyb. and on the 

 disease produced by it in the potato plant. Sc. Proc. Roy. Dub. Soc, XIV (N.S.), No. 10, 11'14. 



