278 



Transactions British Mycological Society. 



The above results are interesting in that they indicate that 

 the "biologic form" of Erysiphe Polygoni on the Swede is able 

 to cause a full infection on the Turnip and Rape, all three being 

 cultivated forms of the same aggregate species Brassica campes- 

 tris Linn., whilst it is only capable of forming a " subinfection " 

 on Cabbage, Kohl-rabi, Broccoli and Kale, which are cultivated 

 forms of the aggregate species Brassica oleracea Linn. Further, 

 that in the case of Charlock {B. Sinapis) the position is very 

 obscure as in five instances full infections resulted, in five other 

 instances " subinfections " only appeared and in a further ten 

 cases no infection at all took place which seems to indicate, 

 either that there was some physiological difference between the 

 Charlock plants used — in one case the plants used were those 

 raised in the greenhouse from seed and in the other were plants 

 found growing wild and simply covered with a cloche — or that 

 some temperature or moisture factor enters into the problem. 



Further it will be seen that in no case did an infection result 

 on any of the hosts used belonging to other families. 



Though no opportunity occurred of repeating and confirming 

 these series the following year, the results indicate that the 

 "biologic form" on Swede is confined to the aggregate species 

 Brassica campestris with powers of slight infection on B. oleracea 

 and probably under certain conditions on B. Sinapis. 



Table IL 

 Inoculations with conidia from Polygonum aviculare. 



These results go to confirm the indications of Table I that 

 the forms of Erysiphe Polygoni on Polygonum aviculare and 

 Brassica campestris are distinct "biologic forms." 



Table IIL 

 Inoculations with conidia from Trifolium pratense. 



Hosts inoculated 

 Trifolium pratense 

 T. hybridum 

 T. repens 

 Vicia Faba 

 Onobrvchis saliva 



No. of 

 inoculations 



4 

 3 

 6 



No. of 

 infections 



+ 4 

 o 

 o 



