594 



STATE BOAKD OF AGRIOULiTURE. 



tion, the longer period of growth being made possible through the breaking 

 down of protein molecules into alkaline compounds. This decomposition, 

 brought about through the activities of the fungus, had the effect of making 

 the reaction of the medium increasingly more favorable for growth up to 

 the point at which the alkaline compounds began to exert a deleterious in- 

 fluence, and then, of slowing up growth until the medium became too toxic 

 for further development. Thus, in a single flask, the organism was able to 

 pass from the limits of acid tolerance on the one hand to an alkaline solu- 

 tion on the other. Various toxic substances thrown off by the fungus were 

 no doubt important in stopping growth before the outer limits of alkaline 

 tolerance were reached, since pH. determinations at the end of the experi- 

 ment proved that the flasks having an acid reaction at the start were only 

 slightly alkaline. Inoculated flasks of broth, having an initial reaction of pH. 

 5.5, showed a gradual change in reaction up until the end of the eighth week, 

 when they had a reaction of pH. 8.2. 



A series of deep culture dishes, with Coons' synthetic solution as the nu- 

 trient medium, were inoculated to determine the effect of reaction of the 

 medium on pycnidium production. 



TABLE 8. 



The limits of fruiting seem to be as wide as those for mycelial develop- 

 ment. The neutral medium again markedly favored vegetative growth, 

 while solutions slightly acid brought forth the largest number of pycnidia. 

 The salient feature in these results is the failure of the solutions acid to pH. 

 5.0 to produce growth in measurable quantities. At first glance, this seems 

 contradictory to results obtained in broth cultures. The solution used in 

 this experiment, however, has more carbohydrate and less protein in its 

 composition than has beef broth. The probabiUty is, that, on account of 

 the nature of the medium, the fungus was unable to adjust the reaction in 

 its favor and that pH. 5.0 is too acid for growth. 



The cultures at different reactions produced a noticeable series of color 

 changes, though there is not such a wide variation as is produced in the case 

 of extreme temperatures. In the alkahne solutions, the fungus produced 

 a pink discoloration, which is never observed in neutral or acid solutions, 

 and the color of the mycelium varied from an almost white to a light blue 

 color. The acid solution produced a bluish or bluish-green mycelium. 



Dissemination. 



The restriction of the pycnidia of the causal organism to the roots and 

 crown of the host plant makes air currents^of little importance in the dis- 



