BIOLOGIC FORMS 



25 



Barberry bushes which had been in the cellar all winter were set 

 out in the field and covered with a heavy muslin cage. Badly rusted 

 straw of wheat was tied around one bush and that of Agropyron repens 

 around another. None of the check plants developed any aecidia while 

 those surrounded with straw were very badly affected. The Agropyron 

 repens material produced mature aecidia 10 days earlier than the wheat 

 material and the aecidia were also developed in greater abundance. 



RESULTS OF INOCULATIONS WITH AECIDIOSPORES AND UREDOSPORES FROM WHEAT 



AND AGROPYRON REPENS 



The field barberries were very probably infected with the rust from 

 Agropyron repens, as will be readily observed by referring to the two 

 tables. Further, the various biologic forms do not show any apparent 

 change as a result of having been transferred to barberry, thus con- 

 firming the results obtained in previous experiments. 



These inoculations, although not extensive, show quite clearly 

 that Puccinia graminis tritici and Puccinia graminis from Agropyron 

 repens do not seem to develop any greater range of infection possi- 

 bility for cereals after having lived for a time on the alternate host 

 the barberry. The incubation period, even on wheat, barley, and ein- 

 korn, was a little longer in these experiments than that of uredo-devel- 

 oped mycelium. 



ADAPTATION OF BIOLOGIC FORMS TO NEW HOSTS 

 Magnus (1894, p. 362) was one of the first to suggest that a 

 particular biologic form might, by constant association with one host, 

 change its physiological capabilities to such an extent as to make a 

 new race out of it. This view was also expressed by Dietel ( 1899, pp. 

 81 and 113) who gave it as his opinion that a given rust formerly at- 

 tacked a number of plants but by long association with one form be- 

 came narrowed to this form more closely, possibly retaining also a 

 somewhat weakened capability of attacking other forms. These 

 authors distinguish between adaptation races (Gewohnheitsrassen) and 

 true biologic forms, the tendency being, under favorable conditions, 



