Oct. 28. 1918 Plasticity of Biologic Forms of Puccinia graminis 231 



NO 00 



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strain capable of attacking rye 

 < ^ normally. Diagram 2 shows 



i i - "§ also that the susceptible species 



of Agropyron used did not act 

 as bridges to normally immune 

 species of this genus. The rust 

 was kept on barley for over a 

 year, but it proved to be en- 

 tirely stable and was therefore 

 discarded. The secalis form 

 likewise remained fixed after it 

 was isolated and attacked its 

 regular hosts vigorously, but 

 could not be transferred to 

 wheat or other normally im- 

 mune hosts, a large number of 

 which were inoculated, but the 

 results of which are not given in 

 the diagram for want of space. 

 Erroneous conclusions might 

 g easily have been drawn from 

 •| the results shown in diagram 3 

 3 if the inoculations had not been 

 g extensive. Here, again, the 

 original rust was a mixture con- 

 sisting mainly of the tritici 

 form but including also a small 

 amount of secalis. Viable 

 spores of secalis were again 

 carried through the moist 

 chamber, and these infected 

 barley, thus accounting for the 

 I'l later events. The secalis form 

 1 1 was kept for about five months, 

 i I but did not change. 



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