APPLE DISEASES 33 
and is also unfavorable to bitter-pit. Most alert commercial 
fruit growers practice thinning. It is an operation essential to 
regularity of bearing. It makes yields regular and bitter-pit 
is consequently reduced. Trees with a light crop and un- 
usually large-sized fruit are most subject to pit. Again, over- 
crowding favors the disease. Manuring has a bearing on the 
development of stippen. The practice is commendable in that 
it not only supplies food, but neutralizes toxic substances in 
the soil. It also affects the moisture content of the soil and 
thus transpiration is modified. The water-elimination process 
in its relation to bitter-pit has been emphasized. Although 
long years of experimentation are necessary to determine the 
effect, if green-manuring were practiced in non-irrigated or- 
chards the disease would probably be reduced. Cover-crops 
are planted by many of the leading apple-growers. These 
crops aid in regulating the water-supply of the apple, and 
when plowed under will conserve the soil moisture. The ques- 
tion of drainage should not be overlooked. This disposes of 
excessive water during the days of heavy rainfall, and conserves 
moisture during drought-periods. The disease is worst in 
low, wet portions of an undrained orchard. Moderation should 
be practiced in the matter of irrigation. The heavy applica- 
tion of water following a drought-period is favorable to stippen 
development. Excess should be avoided, and the aim should 
be to maintain uniformity of moisture conditions. Thorough 
orchard cultivation is advised. This operation affords proper 
aération of the soil and consequent normal and efficient root- 
action. It conserves moisture during periods of dry weather, 
and as a result transpiration is properly regulated. Spraying or 
dusting operations have an important bearing on the problem ; 
for, if neglected, the foliage is almost sure to be diseased and 
therefore less efficient both in the manufacture of food and in 
transpiration. It has been found that diseased leaves trans- 
pire less than healthy ones. 
D 
