I 4 8 TEXT-BOOK OF FUNGI 



Zeocriton and H. trifurcatum all the other host-plants 

 proved persistently immune, although they are capable 

 of being readily infected by other biologic forms of E. 

 graminis. Marchal, in similar experiments, has proved 

 that ascospores taken from the form of E. graminis on 

 wheat can infect wheat, but not rye, barley, or oat. 



So far as experiments have been carried out, it appears 

 that the infection-powers of the ascospores of biologic 

 forms are identical with those of the conidia; thus the 

 specialisation of parasitism is as sharply marked and as 

 distinctive in the ascigerous as in the conidial stage. 

 Since, then, biologic forms show restriction in their power 

 of infection to one species of host-plant, or to a few closely 

 allied species, in the sexual ascigerous stage as well as in 

 the asexual conidial stage, we must admit their claim to be 

 considered as distinct entities. 



The extent to which this specialisation has proceeded in 

 some cases is shown in a recent paper by Salmon on the 

 adaptive parasitism of E. graminis to species of the genus 

 Bromus. The author, as the result of nearly two thousand 

 inoculation experiments, ascertained the presence of 

 a considerable number of well-defined biologic forms, 

 each possessing distinctive powers of infection towards 

 certain species of Bromus. The characteristics of four 

 of these biologic forms are represented in the following 

 schedule : 



