Jan. 13, 1919 



Morphology of Urediniospores of P. graminis 



71 



The uredinia were generally larger on the control plants and smaller 

 on those grown in the dry air. The color of the uredinia grown in humid 

 atmosphere was commonly antique-brown or amber-brown, those 

 produced in the arid atmosphere were amber to argus-brown, while 

 on the control plants they were Sudan to Brussels-brown; in other words, 

 they were darkest in the dry air and lightest in the moist air. 



Effect of Soil Moisture 



In this experiment on soil moisture three series of plants were em- 

 ployed, one of which was very heavily watered, the second moderately, 

 and the third received only enough water to prevent the plants from 

 wilting. Otherwise, the usual methods of innoculation, germination, 

 and incubation were used. The water content of the soil was determined 

 on the basis of the oven-dried method. 



The plants in the wet soil were more severely attacked, and the ure- 

 diniospores developed on them were larger than those in either the con- 

 trol or the dry series. The series that suffered from drouth produced the 

 smallest spores. There was no apparent difference in the color of the 

 uredinia or spores. Table XV gives the detailed results. 



Table XV. — Results showing the effect of soil moisture on the physiology and morphol- 

 ogy of urediniso pores of Puccinia graminis tritici on wheat 



Ex- 

 peri- 

 ment 

 No. 



Soil moisture. 



Water Water 

 applied, content. 



Degree of infection. 



Result. 



Spore dimensions. 



Size limits. 



Modes. 



900 

 850 

 400 

 230 

 150 

 100 



Per cent. 

 3 = -l4 

 31-65 

 17. 12 

 16.28 

 9>24 

 S-38 



Heavy' . . . 

 ....do.... 

 ....do..., 

 ....do..., 

 Moderate 

 ....do.... 



22. 72-43. 84X16.96-22.40. 

 26. 24-40. 96X17.60-22. 72. 

 25. 28-40.32X16.96-23.04. 

 25.92-40.00X16.96-23. 36. 

 24-96-38. 72X16.32-23.36. 

 22.40-38.08X16.64-21. 76. 



33.28X19-84 

 33. 28X20. 16 

 32.64X19.84 

 32.64X20. 16 

 32.32X19.84 

 30.40X19. 20 



Effect op Illumination 



In testing the effect of illumination two series of plants were em- 

 ployed, one of which was kept beneath a double-layer muslin cage, 

 while the other one was exposed to the direct sunlight in the greenhouse 

 (Table XVI). As the experiment was conducted during the winter 

 months the light was at no time exceptionally bright. The cultural con- 

 ditions, except for the variation in light intensity, were maintained the 

 same for both series. The light readings were taken daily, sometimes two 

 and three times a day, with the Clements photometer charged with a 



