312 Proceedings of Indiana Academy of Science 



is restricted to that species. However, not all of the varieties of T. 

 pyatense were found to be susceptible. An examination of tables I 

 and II shows an interesting situation, the North American varieties 

 being- generally quite su.sceptible, while the European show in general 

 rather high resistance. The Chilean seemed intermediate between the 

 two. Figure I (A and B) shows the difference in susceptibility shown 

 by a flat of the variety Tennessee 2138 and a flat of the variety Italian 

 54779. 



What the significance of this situation may be, is hard to say. It 

 is possible that the long presence of mildew in Europe may have had a 

 selective effect, possibly preventing the formation of seed in susceptible 

 plants. This would necessitate a very marked effect of the mildew on 

 seed production. On the other hand, the absence of mildew in this 

 country would preclude any such selection. However, as far as the 

 writer has been able to determine, no one has noted red clover resistant 

 or immune to mildew in Europe. On the other hand, judging from the 

 lack of comment on the disease, it may not be serious at the present 

 time, possibly indicating resistance but not complete immunity. It is 

 useless, however, to theorize until we have a better knowledge con- 

 cerning the biology of this disease and the relation of the race on T. 

 prutense to a greater number of other species of Trifolium, especially 

 native wild species, and until we know whether differences exist between 

 the mildew in North America and Europe in its ability to attack 

 varieties, whether the mildew in this counti-y has been recently intro- 

 duced or whether climatic conditions of the past year have been re- 

 sponsible for the development and conspicuous appearance of the disease, 

 and what the effect is on the clover plant, especially upon seed production. 



Another thing noticeable in tables I and II is the presence of re- 

 sistant individuals in all except three of the varieties tested. It is likely 

 that if a larger number of plants of these three had been tested, 

 resistant plants would also have been found among them. Figure I 

 (A' and B') .shows a leaf from a susceptible and a leaf from a resistant 

 plant of Ohio 2135. 



As we have already noted the discovery or development of resistant 

 varieties suggests the most likely control. Unfortunately in most cases 

 the presence of one or more undesirable qualities in resistant varieties 

 complicates the situation. Thus several of the resistant European 

 varieties apparently are not especially adapted to our climate, since those 

 in the field during the comparatively mild winter of 1921-1922 winter 

 killed badly. Prof. A. T. Wiancko'' has stated that in his field tests of 

 clover varieties, the Italian killed out entirely during the winter of 

 1920-1921. In consequence it appears very doubtful if these varieties 

 would be of much value except for hybridizing work. Unless other 

 European varieties prove to be hardy, the most promising method of 

 obtaining mildew-resistant strains appears to be by the selection of 

 resistant individuals in American varieties. 



* Wiancko, A. T. Report of the Director, Purdue University AiLrricultural Experiment 

 Station. 1921:37. 



