202 
E. B. MAINS 
Table V 
Effect of Carbohydrate Supplied to the Seedling Upon the Development of Puccinia 
Sorghi 
Solution 
No. of Plants 
Used 
No. of Plants 
Infected 
Av. Growth per 
Plant per Day 
Starch 15% 
10 
9 
3.4 mm. 
Starch 15% + Knop's 
10 
3 
1.6 " 
Starch 15% + Knop's - N 
ID 
5 
5-1 " 
Cane sugar 15% 
12 
3 
.9 " 
6 
3 
3-7 " 
Cane sugar 10% + Knop's 
12 
6 
3-3 " 
Cane sugar 10% + Knop's — N 
13 
5 
3-7 " 
6 
4 
6.0 " 
Cane sugar 3%. ...... 
21 
13 
7.6 " 
Cane sugar 3% + Knop's 
21 
13 
11.3 " 
Maltose 3% 
7 
5 
4-9 " 
Maltose 3% + Knop's 
7 
4 
9.1 " 
Dextrin 3% 
6 
3 
II. 0 " 
Dextrin 3% + Knop's 
7 
2 
12.6 " 
Dextrose 3% 
18 
5 
4.8 " 
Dextrose 3% + Knop's 
18 
9 
9.8 " 
50 
3 
2.6 " 
13 
0 
•4 " 
Distilled water 
45 
8 
2.3 " 
present in the host upon which the rust as well as the host was able to 
draw. When reinoculated this was exhausted and there was no infec- 
tion of hosts in either distilled water or Knop's solution. The results 
of these experiments indicate that soluble carbohydrates are necessary 
for the development of the rust. 
Carbohydrates Supplied to Pieces of Leaf 
In the earlier part of this work contaminations occurred which 
were due to working with imperfectly sterilized leaves and especially 
with rust spores having saprophytic fungus spores mixed with them. 
It was evident that to obtain trustworthy results not only sterile 
host plants were necessary, but that pure cultures of the rust must 
also be obtained. This was done as follows : 
Pure Cultures of Puccinia Sorghi 
The only worker who has given any account of a method to grow 
rusts in pure culture appears to be Marshall Ward (1902^/) working 
with Puccinia dispersa upon the bromes. His method consisted in 
obtaining sterile cultures of the bromes by sterilizing the seed by 
