Jan. 13, 1919 Morphology of Urediniospores of P. graminis 



73 



EXPERIMENTS ON CULTURAL METHODS 



It was thought well worth while conducting a few experiments to 

 ascertain the effect of the age of the host plant at the time of inoculation 

 on the rust growth and on the size of the urediniospores, also to find out the 

 length of time during which urediniospores retain their vitality and what 

 is the relation of the age of the fungus to the morphology of the uredinio- 

 spores. The results obtained (Table XVIII) show that the suscepti- 

 bility of the host is little dependent on its age, and that urediniospores 

 retain their vitality for a considerable length of time with no perceptible 

 variation in size. 



Table XVIII. — Results showing the effect of age of host plant on the morphology of 

 urediniospores of Puccinia graminis avenae 



Experi- 

 ment 

 No. 



Host plant. 



Avena sativa . 



do 



do 



do 



do 



do 



Age of 

 plants 

 inocu- 

 lated. 



Days. 



7 



7 



14 



35 



Spore dimensions. 



Size limits. 



• 00-35 



• 04-35 



• 96-34 



• 96-35 



• 76-37 

 ■ 72-35 



. 52X16. 00-22. 08 

 . 52X16. 96-22. 08 

 . 88X14. 72-22. 72 

 . 84X16. 00-22. 40 

 . 12X16. 64-21. 76 

 . 84X16. 00-22. 40 



Modes. 



2g. 44X19. 20 

 29.44X19- 52 

 29. 44X19. 20 

 29.44X19. 20 

 29. 44X19. 20 

 29. 12X19. 20 



EFFECT OF THE AGE OF HOST PLANTS ON THE DEVELOPMENT OF THE 

 RUST FUNGUS AND SIZE OF THE UREDINIOSPORES 



Oats were here used as host plants, because they were found to thrive 

 better under greenhouse conditions than wheat, barley, or rye. Inocu- 

 lations were made when the plants were 7, 14, 21, and 35 days old, count- 

 ing the age from date of sowing. The 7 and 21 days series were later 

 duplicated. In all cases the plants were inoculated with a uniform 

 amount of fresh urediniospore material of P. graminis avenae and cultured 

 under similar and normal conditions. 



The plants i week old were slightly more vigorously affected (Table 

 XVIII) at first, but at the end of 10 days the infection was heavier on 

 the older plants, and especially so on those that were three weeks old at 

 the time of inoculation. , From Table XVIII it will be seen that the 



