BIOLOGIC FORMS 27 



much more severe. Areas of the leaf two centimeters in length were 

 often almost covered with pustules, some of which attained a length of 

 seven millimeters. 



A number of other trials were made, the last after the rust had 

 been confined to einkorn for 17 months. In one experiment the re- 

 sults were just the opposite of what were expected. This is explained 

 by the fact that lack of greenhouse space necessitated keeping the ein- 

 korn plants inoculated with einkorn rust in a draught of cold air. 

 There were only a few wheat uredospores available in inoculating the 

 wheat, so, in this experiment, einkorn-by-einkorn inoculations were not 

 so successful as einkorn-by-wheat. In subsequent trials, however, un- 

 der uniform conditions, the results first described were substantiated. 



The conclusion, then, is justified that by confining Puccinia gram- 

 mis tritici to einkorn for successive generations throughout a year or 

 more the rust adapts itself somewhat to its new host and loses, at least 

 to a slight degree, its power to infect the original host. It would no 

 doubt require a very long period of time to fix this character in the 

 plant to such a degree as to make it a new biologic form. But there is 

 very evidently such an adaptational tendency (see Plates II and III). 

 It must be noted, however, that this new character is not so firmly 

 fixed that it cannot be overbalanced by environmental factors. The ex- 

 perimental production of new forms is apparently possible, but a long 

 period of time is required. 



The change in the fungus manifests itself not merely in the para- 

 sitic tendency toward the host but in the morphology as well. Wheat 

 and einkorn were inoculated with spores from the same plant. The 

 uredospores after growing for a year on wheat averaged 37.85x22.76 /* 

 while those grown on einkorn for a year measured 33.58x21.79 /*. 

 When einkorn was inoculated with Puccinia graminis tritici aecidio- 

 spores, the resulting uredospores were more nearly identical with the 

 wheat-rust spores in length. The width, however, remained practically 

 the same. The average size of these spores was 35.92x21.69 /*. 



SUMMARY OF PART I 



1. Direct transfers of Puccinia graminis have been made from 

 oats to both wheat and rye. The rusts from oats and barley used in 

 these experiments could be transferred to rye more easily than those 

 used by Carleton or those used by Freeman and Johnson. The barley 

 rust, however, did not prove as versatile as the strain used by Freeman 

 and Johnson. 



2. The use of anesthetics has some effect in rendering an immune 

 plant slightly more susceptible to the rust; leaf injury apparently had 

 no effect. 



3. High fertilization, by increasing the virulence of the attack 



