APPLE POWDERY MILDEW AND ITS CONTROL. 13 
proportional to the sulphur content of the spray mixture employed. 
If the first spraying is delayed until the apples are an inch or more 
in diameter and a spray mixture containing a relatively large amount 
of sulphur is used, a heavy shedding of fruit and foliage may be 
expected to follow. The leaves that fall are turgid and green and 
look in all respects fresh and normal. In bad cases the foliage 
shedding may be so severe as to leave the trees bare. The fruit that 
drops is also normal in appearance and may amount to 50 per cent 
of the crop. The loss of foliage is usually more than replaced by 
the vigorous production of new, extra-large leaves. Spraying with 
very weak mixtures brings about an increased foliage growth with- 
out causing leaf dropping. It is therefore evident that this unusual 
foliage production is not a reaction to any leaf pruning caused by 
spraying. 
It might seem that the increased foliage growth is only the normal 
production of new growth to be expected as a result of the mildew 
control. That this, however, is not the case and that sulphur spray- 
ing has an actual stimulating effect seems to be a clearly established 
fact. Plate V, figure 1, shows two twigs from a tree that was not 
sprayed until considerable growth had been made. The first leaves 
that came out in the spring, those at the bases of the twigs, were of 
fair size. Gradually, as the new leaves appeared, they became more 
and more infected with mildew, and when the twigs had grown to 
the length indicated by the letter 7 in the figures, the leaves were 
small, distorted, and badly diseased. Very little more growth could 
have been expected. At that time the tree was sprayed with a mix-— 
ture made by dissolving sulphur in carbon disulphid and emulsify- 
ing this solution with ammonia soap. Such a spray leaves a very © 
fine coating of sulphur all over the foliage. Almost immediately 
growth was resumed and conspicuously large leaves were sent out. 
The photograph reproduced as Plate V, figure 1, was taken some 
time after the spraying was done, and no spray had been applied 
meantime. In other words, the extra growth of leaves took place 
after the spray was applied and their large size was not due to 
killing any mildew that was on them or to preventing infection, 
because they -were not out at the time the spraying was done, and 
therefore they received none of the application. Thus, it seems 
evident that the spraying itself stimulated a new growth of foliage. 
One type of fruit injury that may result from sulphur spraying is 
shown in Plate VI, figure 1. A strong dosage of iron-sulphid mix- 
ture was applied after the fruit had become partly grown. Shortly 
after the application was made there were several days of very hot 
weather, and on the exposed sides of the fruit, where the hot sun had 
