74 



Journal of Agricultural Research 



Vol. XVI, No. 2 



size of the urediniospores was remarkably uniform regardless of the age 

 of the host; nor was there any difference in the shape and color of the 

 spores. 



The junior author has also obtained very successful infection on mature 

 plants of more than a hundred different varieties of wheat, grown in the 

 greenhouse and artificially inoculated with P. graminis tritici. This 

 latter work was conducted at the Kansas Agricultural Experiment 

 Station in cooperation with the United States Department of Agriculture. 



ElfFKCT OF THE AGE OF THE) RUST FUNGUS ON TftB VITALITY AND 

 MORPHOLOGY OF THE) UREDINIOSPORES 



Fromme (4, p. 504) states that De Bary found the length of time during 

 which urediniospores of P. graminis retain their vitality to vary between 

 one and two months, and that Bolley obtained a 5 per cent germination 

 with urediniospores of P. graminis after exposure to air and sunlight 

 during the month of August. The object of this experiment was to 

 determine the vitality of the urediniospores after different periods of 

 association with their respective hosts and effect of the length of associa- 

 tion on the rust morphology. 



For the determination of the first phase of the experiment inoculations 

 were made (Table XIX) with rust material at different stages of the 

 development of the uredinia. Transfers were made when the uredinia 

 were merely beginning to break through the epidermis and two and four 

 weeks afterwards. There was no apparent difference in the degree of 

 infection produced by these methods of inoculation. 



Table XIX.- 



-Results showing the effect of age of the fungus on the morphology of 

 urediniospores of Puccinia grmninis 



In determining the effect of the age of the fungus on the morphology 

 of the spores, measurements were made at different stages of the develop- 

 ment of uredinia, beginning 7 days after inoculation and ending with 

 63 days. Three biologic forms of P. graminis were used in this experi- 



