FROMME: THE CULTURE OF CEREAL RUSTS 511 
by this method and the fungus has gone through thirty-seven 
generations of the uredo stage with no decrease in. virulence. 
It was soon found that even more simple methods of inocula- 
tion are equally if not more efficacious than the application of 
spore suspensions with an atomizer. The plants to be inoculated 
are first thoroughly atomized with water. A well-infected culture 
pot bearing fully ripe pustules is then held in a horizontal position 
immédiately above them and given a vigorous shaking. The 
spores that fall from above are caught in the small drops of water 
provided by the spray. If the culture used is heavily infected the 
falling spores may be seen as yellow clouds. The inoculated plants 
are then covered for twenty-four hours. Four pots of seedlings 
can be inoculated simultaneously from the same culture and a 
uniform degree of infection secured on all four by placing them 
close together and holding the culture somewhat higher than for 
inoculating a single pot. It was found that spraying prior to 
inoculation could be dispensed with but the pustules secured were 
somewhat less numerous than when the spray was applied. To 
secure the best results the culture used for transfer must be heavily 
infected and the transfer made shortly after the ripening of the 
pustules. If transfer is delayed more than a week after sporula- 
tion begins, inoculation with a spore suspension must be resorted 
to. : 
Very numerous and uniformly distributed pustules were se- 
cured and maintained by this dry-spore method of inoculation. 
The approximate number of pustules per plant in a culture was 
determined in the following way. 
* For facility in counting the surface area of the pot it was divided 
into smaller areas with strips of cardboard. The number of 
plants and infected parts on each of the smaller areas was then 
easily ascertained. Ten plants were then taken at random from 
the culture, removed to the stage of a binocular, and the number 
of pustules on the infected parts determined. TABLE 1 shows the 
amount of infection on a typical culture. In this culture all of 
the first leaves were infected, 62.5 per cent of the second leaves, 
and 29.1 per cent of the sheaths. The average number of pus- 
tules on the first leaves of the ten selected plants was 574.4, on the 
second leaves, 22.9, and on the sheaths, 1.4. The small number of 
