274 Transactions British Mycological Society. 



SOME OBSERVATIONS ON ERYSIPHE 

 POLYGONI DC. 



By G. 0. Searle, B.Sc, P. A. S.I. 



(Bd. of Agric. Research Scholar, Botany School, Cambridge.) • 



The work described in this paper was carried out by the author 

 during 19 13-14 in the Mycological Department of the South- 

 Eastern Agricultural College, Wye. 



The war caused a cessation of the work in August. 1914, and 

 no opportunity of continuing the investigation or of publishing 

 the results has occurred until now, except in the one instance 

 given below. Though far from complete and though a con- 

 siderable time has elapsed since they were undertaken, it was 

 thought that these observations might contain sufficient points 

 of interest to be worthy of publication. 



My thanks are due to Mr E. S. Salmon for the many suggestions 

 and great help he gave me. 



The investigation, as originally conceived, fell under the 

 following three heads: 



(A) The Comparative Susceptibility of Varieties of Swedes and 



Turnips to the "Swede Mildew" {Ervsiphe Polvgoni 

 DC). 



(B) The Specialisation ul Parasitism within the Morphological 



Species Erysiphe Polygoni DC. 



(C) The Method of Over-wintering of the "Swede Mildew" 



{Erysiphe Polygoni DC). 



(A) In the case of the first problem to be attacked, the result 

 of the field trials for 1913 have already been published in full 

 elsewhere (12), and will only be very briefly described here. 



Samples of seed of thirty-three varieties of Swedes, forty-two 

 varieties of Turnips and two varieties of Rape were obtained 

 from five well-known seeds-merchants in England and Scotland. 



These seeds were sown, on June 9th, loth, and 12th, in small 

 plots measuring ten links square, i.e. one-thousandth of an acre 

 each, on old lucerne ley which had been ploughed and dunged 

 but had received no artificials. The plots were cultivated and 

 thinned in the usual way. On August 23rd the conidial stage 

 of Erysiphe Polygoni was found on Swedes in a field situated at 

 some distance from the plots, and on the 28th of August sufficient 

 material was collected from this field to carry out the infection 

 of the plots in the following manner. 



