?tors limiting its distribution. Tisdale-'^, W. H. , has 

 3hown, for Fusarium wilt of flax, : tare at 



which the host is mo3t injured fc disease corresponds to 

 that fcv Lmum growth cf the parasite in cultures, 

 many parasitic organisms it is probable th i temperature 

 ranee within which serious infection. of their hosts may occur 

 naturally, is comparatively small. This, as well as differ- 

 ences in moisture conditions, may largely account for many of 

 the striking differences observed in the occurence of nany 

 plant diseases from season to season and from one region to 

 another. Many other observations aside from these given above 

 might be mentioned in this connection, but it seems to be 

 clear enough that the pathological or agricultural point of 

 view demands much more thorough going knowledge than we yet 

 have, concerning the temperature relations of parasitic fun - 

 It was thought that the results obtained in the present study 

 might ultimately be of value in pathological work. 



Considering the limited time available for this study, 

 it appeared better to confine the experimentation to the four 

 forms mentioned above, and to subject the results to a crit- 

 ical study than to include a larger number of forms, with 

 the accompanying necessity of treating the results in a more 

 superficial manner. Our knowledge regarding the physiology 

 of fungi , as well as that regarding plant temperature rela- 

 tions, should be increased first by intensive studies of a 



(6) Tisdale, W. H. Relation of temperature to the grow 



and infecting power of Pu sari urn Lini . Phytopathology 

 7 : 356-360, 1917. 



