190 PJTYTOPHTHORA PARASITICA. 



Trow 1 , when working with Pythium ultimum, found it only 

 necessary, in order to get a pure and copious growth of the fungus, to 

 sterilise potatoes in suitable glass pots and inoculate them with a 

 trace of the mycelium from the aerial growth developed on inoculated 

 cabbage and rhubarb leaves projecting above the surface of water 

 in Petri dishes. It, therefore, at first, seemed easy to get similarly 

 a pure culture of Ph. parasitica from the aerial mycelial growth 

 obtained about half a centimetre high in 24 to 48 hours by 

 keeping a freshly diseased leaf in a Petri dish containing a little 

 tap water, but when inoculations were made on sterilised potatoes, 

 carrots bread paste, acidified bread paste, glucose meat-extract 

 agar acidified glucose meat-extract agar, prune juice agar and 

 Ricinus leaf juice agar, it was invariably found that bacteria 

 contaminated the media and overgrew the fungus. Attempts 

 were made to get a bit of a hypha free from bacteria by nipping it off 

 just below its apex by means of a hot platinum needle but the 

 hypha being unseptate the bit on the needle lost its protoplasm 

 from its cut end ; thus while getting rid of bacteria its vitality 

 was destroyed. A living potato washed with formalin and cut into 

 two by a sterile knife was inoculated on its cut surface. An aerial 

 mycelial growth soon developed but again was not free from 

 bacteria. 



A pure culture was ultimately got by means of the following 

 technique. 



A diseased leaf was got from the field. It was well washed 

 with sterilised water to get rid of foreign matter as much as possible 

 and kept in a covered sterilised Petri dish containing a little sterilised 

 tap water. The Phytophthora hyphse spread out on the surface of 

 the water and bore a crop of sporangia the next day. They readily 

 discharged their zoospores in a drop of sterilised tap water. This 

 drop was used to inoculate a clean well washed newly opened leaf of a 

 seedling grown in the laboratory, thereby further minimising the 

 presence of saprophytic fungi. The seedling was kept in a moist 



' Trow, A. H. Observations on the Biology and Cytology of Pythium ultimum, n. sp., 

 Ann. Bot., XV, 1901, p. 279. 



