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E. B. MAINS 
inoculation to remove this waxy substance. Since this method would 
cause contamination in this case, other means were resorted to. It 
was noticed that drops of water often condensed upon the leaves during 
cool nights. Spores were placed in these with resulting infection. As 
carried out later, the leaves were rubbed with sterile cotton wrapped 
around sterile forceps and soaked in sterile distilled water. In the 
drops left adhering to the surface of the leaves, a loop full of uredo- 
spores was placed. In this way very good infection was obtained. In 
most cases, the spores used, after the combined dilution and washing 
to which they were subjected, were probably sterile, but in order to 
make sure that there was no contamination, spores from the resulting 
infection upon these plants were used to inoculate other sterile plants. 
These spores were taken from the other side of the leaf from that on 
which the original inoculation had been made. By this means they 
were obtained from a sterile surface which had not been touched in 
the original inoculation. The plants of this second series, when once 
infected, will be reinfected by the spores produced on them as long as 
they are in good condition, if kept at a temperature favorable for 
spore germination (Plate V, figure i). 
A second means of obtaining pure cultures of Puccinia Sorghi was 
by means of cut pieces of leaf themselves. Uredospores which had 
been removed from clean parts of infected plants were diluted in 
sterile distilled water. Drops from this spore dilution were placed on 
the surface of pieces of leaf which had been cut from sterile corn plants, 
and floated upon carbohydrate solutions. A few capsules were con- 
taminated by saprophytic fungi, but more often capsules were obtained 
which were free from these and the rust produced in such capsules 
was used to inoculate pieces of leaf in like manner. By inoculating 
fresh cultures about every two or three weeks, a pure culture of the 
rust can be kept on hand (Plate V, figure 2). 
Experiments 32-41. — ^These experiments were carried out with 
pure cultures of both host and rust. Cut pieces of sterile corn leaf 
were floated upon sterile solutions of 3 and 6 percent cane sugar, 3 
percent cane sugar plus Knop's, 3 percent dextrose, 3 percent 
dextrose plus Knop's, 3 percent maltose, 3 percent maltose plus 
Knop's, Knop's, and' distilled water. After one to three days, 
uredospores from pure cultures of Puccinia Sorghi upon sterile plants 
were diluted in sterile distilled water and a drop of this spore suspen- 
sion was placed on each piece of leaf. The capsules were placed in a 
dark chamber at 20° C. 
