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Proceedings of Indiana Academy of Science 



ing inoculum is sown on as many pots of wheat as possible in plant 

 covers or Wardian chambers. From the infection obtained, the set of 

 varieties is inoculated. 



After inoculating, the plants are placed on the greenhouse bench, 

 possibly beside a set inoculated with another culture. As the humidity 

 of the greenhouse does not reach the saturation point, and the seedlings 

 are not grown thickly enough to provide such a condition among them, 

 no infection results from one culture to the other on the bench. After 

 notes are taken, the plants are discarded. If further investigations 

 are carried out, the rust inoculum is obtained again from the lantern 

 globe. 



10. Pure Lines of the Rust Fungus. In the course of the investi- 

 gations of the leaf rust of wheat Piiccinia triticina, it became evident 



Fig. 4. Sinprle spore cultures. Spore picked up from petri dish on binocular stage 

 (A) by wet glass needles (C) and placed on wheat seedling (B). Culture covered with 

 lantern globe (D) . 



that the rust organism as collected consisted of more than one strain. 

 In order to be sure that the results obtained were characteristic of one 

 strain of the organism and not due to a mixture of several strains, it 

 became necessary to devise a method for obtaining a pure culture or 

 pure line of the rust fungus. This can be done, with certainty only, by 

 starting from a single spore. After a number of unsuccessful attempts 

 to obtain such cultures the following method was found to work veiy 

 successfully. 



Urediniospores of a collection of the rust are gently dusted into a 

 petri dish (fig. 4). This dish is placed under the highest powers of a 

 binocular and a single urediniospore located, considerably .separated from 

 others. This is picked up by touching it with a wet glass rod drawn out 

 to a fine point. By means of this glass needle, the spore is transferred 

 to the moistened blade of a wheat seedling. Usually ten such plants, 

 which have been grown under a lantern globe as mentioned above, are 

 so inoculated. The culture is observed daily and as soon as the first 



