238 AMERICAN JOURNAL OF BOTANY [Vol. 9 



DESCRIPTION OF PLATES 

 PLATE XI 



FIG. I . View of one of the four series of pots of experiment V of the soil-culture studies, 

 illustrating the difference in vigor of growth between plants receiving different nutritive 

 treatment. 



FIG. 2. On the left, a pot containing 5 plants of group A (grown in sand) ; and on the 

 right a pot containing 5 plants of group F (soil highly fertilized with NaNO 3 ) ; experiment 

 V of the soil-culture studies. 



PLATE XII 



FIG. 3. Crown rust of oats. A rust mycelium exhibiting a very marked tendency 

 towards teleutospore production. The first sorus produced by the mycelium (in the center) 

 is a uredosorus. The others are teleutosori. Photographed with Zeiss 3.5 cm. microplanar. 

 X2 4 . 



FIG. 4. View of infected leaves of a semi-starved plant and of a richly fed plant of 

 soil-culture experiment V, showing larger size of pustules on more luxuriant host plant. 

 Photographed with Zeiss microplanar. X 15. 



FIG. 5. Same as figure 4. X 10. 



