Beax Axtiiracxose. 



291 



Of course the explanation of this is, not that the rainy seasons caused 

 the disease, but that they were especially favorable to the spread and 

 development of the fungus (Colleototrichum lindemuthianum) , which 

 is the real cause. As a natural result of this there was an increasingly 

 large amount of infection carried over in each succeeding bean crop, 

 so that the following season always found a larger number of diseased 

 plants in the bean fields. These two factors 

 contributed largely to the epidemic character 

 of the malady which became so marked in igo6. 

 Quite a large number of germination tests were 

 made during the winter of 1907 on the 

 bean seed of the igo6 crop from various parts 

 of this and adjoining states. This seed showed 

 a general average of more than 20 per cent, 

 of anthracnose in it, many samples showing a 

 very much larger proportion than that, while a 

 very few showed as little as 4 per cent. There 

 was eveiy reason to believe that this seed, if 

 planted during the season of 1907 would result 

 in another epidemic of the pod spot. Just the 

 reverse proved to be the case, but this was due, 

 not to the want of the disease in the fields, 

 as I shall point out, but chiefly to one fact, 

 that the season was exceptionally dry, in par- 

 ticular at those tim.es when the fungus was 

 most in need of rain for its development and 

 distribution, namely, during the early stages of 

 germination and grow^th of the seedlings, and 

 later at the time when the pods were being 

 formed and developed. As a matter of fact, the 

 disease was very common in practically all of 

 the bean fields in the State 

 showed as high as 90 per cent, of the pods spotted with the anthracnose, 

 but owing to the dry weather these spots never developed sufficiently to 

 penetrate the pods to any extent, and thus materially affect the beans 

 within. The bean seed of the crop of 1907, therefore, has been found to be 

 remarkably free from the pod-spot; although in almost any sample a bean 

 will be found here and there that is distinctly spotted. On account of 

 the inadequate greenhouse accommodations during the past winter, 

 we were unable to test out thoroughly samples of the 1907 seed, but 



Fig. 219. — Seedling, just up, 

 showing the disease on the 

 cotyledons. 



Careful examination of a number of fields 



