RELATION OF SOME RUSTS TO THEIR HOSTS 
205 
The results of these experiments are given in the following table. 
Table VI 
Effect of Carbohydrates Supplied to Cut Pieces of Leaf Upon the Development of 
Puccinia Sorghi 
Cane sugar 6% 
Cane sugar 3% 
Cane sugar 3% + Knop's. 
Dextrose 3% 
Dextrose 3% + Knop's. . . 
Maltose 3% 
Maltose 3% + Knop's. . . . 
Knop's nutrient 
Distilled water 
pustules large 
pustules few, small 
3 pustules, small 
Of the pieces of leaf on Knop's nutrient solution which were in- 
fected, one piece had one very small pustule, while the other had three 
very small pustules which were light in color, very unlike the brown 
color of a vigorous rust. The infection upon carbohydrate solutions 
varied from a few large brown pustules to a mass of pustules which 
covered nearly all the area of the piece of leaf (Plate V, figure 2). 
All the pieces of leaf which were on carbohydrate solutions had the 
cells of the mesophyll and parenchyma sheaths filled with starch. 
Pieces of leaf on Knop's solution and distilled water showed no sign 
of starch. At the end of 14 days, most of the pieces of leaf were alive, 
as was shown by plasmolyzing with strong KNO3. 
These results agree with those obtained with plants in nutrient 
solution. 
Effect of Nutritive Solutions upon Spore Germination and 
Continuance of Growth 
In this work, the uredospores of Puccinia Sorghi were sown upon a 
number of different nutritive solutions. Compounds were used which 
it was thought would likely be utilized by the rust in its host. 
The method employed in the first two experiments was to remove 
uredospores from an infected plant as carefully as possible and float 
them on the surface of a sterile solution of the nutrient material to be 
used. Hanging drops of this spore suspension were then made. 
In order to avoid the work necessary for making a large number of 
van Tieghem cells, the hanging drops were made upon the lid of a 
