•212 PHYTOPHTHORA PARASITICA. 



found to be equally successful for cultures of Ph. Faberi. Oospores 

 of the castor Phytophtkora were produced in these media quite 

 luxuriantly, especially in French-bean juice agar. Both these media 

 give a very poor growth of the fungus if they are older than about 

 two months. It has been found advisable to use freshly made 

 cultures. In old media the fungus grows very slowly and produces 

 very scanty aerial mycelium, more scanty sporangia and rarely 

 oospores. 



The acidity of French-bean juice agar and of oat juice agar has 

 been found to be + 2 Fuller's scale for each. Of course there must 

 have been slight variations in the different sets of these media 

 prepared at different times. The following notes give a brief 

 account of the growth of Phytophtkora from Ricinus on the various 

 media tried. 



French-bean (Phaseolus vulgaris) juice agar (50 + 10 + 500). — 

 Soon after inoculation, the growth was confined to the surface of the 

 medium ; in a couple of days a rich aerial growth of the mycelium was 

 produced which eventually filled the whole tube. The hyphae of the 

 aerial mycelium remained unbranched for long distances ; when 

 observed in a mass they presented a regular even surface. The hypha? 

 on the surface of the medium showed attempts at branching, most of 

 which were abortive, hence an irregular thorny appearance was given 

 to these hyphse. The submerged mycelium was profusely branched. It 

 also contained irregularly swollen hyphse. The aerial and submerged 

 mycelium produced a rich crop of sporangia and ' ; resting' 1 conidia. 

 As we have seen oospores were luxuriantly formed, embedded in this 

 medium, but only when it was inoculated with the fungus grown on 

 another medium. This medium was prepared in almost the same way 

 as Lima-bean juice agar by Clinton. 1 Fifty grammes of dried beans 

 were powdered in an iron pestle and mortar, made up with about 

 300 c.c, of water, then either simmered for half an hour or cooked in 

 the steam of a Koch's sterilizer for half an hour. The latter course 

 was preferable as in the former case there was a likelihood of cracking 

 the vessel if it were of glass or of charring the pounded beans if it were 



1 Clinton, G. P. loc. cit., 1907-1908, p. 898. 



