72 



Journal of Agricultural Research 



Vol. XVI, No. 2 



printing-out photographic paper. The percentage of intensity was de- 

 termined by means of a standard print made at noon of a bright sunny 

 day in the fall of 191 5. 



Table XVI. — Results showing the effect of illumination on the physiology and morphol- 

 ogy of urediniospores of Puccinia graminis tritici on wheat 



Ex- 

 peri- 

 ment 

 No. 



Degree of infection. 



Result. 



Spore dimensions 



Size limits. 



Modes. 



Heavy. . , 

 ....do... 

 ....do... 

 Weak. . . . 



...do... 

 Moderate 



25. 2S-40. 32X16. 96-23 

 25. 60-40. ooX 16. 00-23 

 22. 40-40. 32X 16. 32-32 

 22. 72-35. 84X 16. 96-22 



21.76-36.48X17. 2S-22 

 23. 04-40. 64X 14. 72-22 



32.64X19.84 

 33.28X19-84 

 32.00X19.84 

 29. 76X19-53 

 29. 12X19- 84 

 29.76X18.88 



The rust consistently developed better in fairly high intensities than in 

 the lower ones. The size of the urediniospores, as given in Table XVI, 

 responded in similar manner. The color of the uredinia in the shade 

 varied from antique-brown to Sudan-brown, while of those in the light 

 ranged from Sudan-brown to argus-brown — that is, somewhat lighter in 

 shade than in the open. It appears that in as much as the photosyn- 

 thetic activities of the host plant are affected by the light intensity in so 

 much does the function and structure of the rust fungus depend on the 

 same factor. 



Effect of Excessive Nitrogenous Fertilization 



The preliminary results obtained by the writers seem to indicate that 

 an excessive amount of sodium nitrate, inhibiting the growth of the host,, 

 also inhibits the development of the rust and dimimishes very percepti- 

 bly the size of the urediniospores, as is shown in Table XVII. This is in 

 accord with Sheldon's {10) carnation rust experiments which showed 

 that the kind of soil that favored the growth of the host also favored the 

 attack of the rust, and that, as a rule, the period of incubation of the rust 

 was inversely proportional to the vigor of the host. The plants were 

 considerably shriveled by the chemical and badly dried two weeks after 

 application. The rust, however, had made a fair start on one blade out 

 of the eight inoculated and developed uredinia of moderate size and ex- 

 tent. The uredinia were darker in color than those developed under 

 normal conditions. 



