APPLE DISEASES 29 
With these facts in mind the most important theories, which 
have been championed to explain the killing and drying out of 
the affected cells, may now be examined. 
(1) The injury is due to a rapid transpiration, or loss of water, 
from the cells, thus bringing about a concentration of the sap 
in those cells nearest the sap-tubes. This concentration of sap 
which is chiefly a concentration of the acids, results in the injury 
and death of the cells. The concentration of the cell-sap is 
therefore the immediate cause as outlined by this theory, and 
this concentration is increased by an insufficient water supply 
as well as by excessive loss of water. Those who cling to this 
theory believe that it accounts for the development of the 
disease both in storage and on the trees, and in the latter case 
for its appearance in wet as well as in dry weather. The 
following facts form the basis for this proposed explana- 
tion: (a) Warm, dry weather favors transpiration. (6) Dur- 
ing such weather the soil is deplete in moisture and there- 
fore cannot supply the cells with water sufficient to offset 
the rapid loss by transpiration. (c) During the wet season the 
apple-fruit grows very rapidly and the net-work of sap-tubes is 
not able to keep pace with the growth of the pulp-cells and the 
proper balance is disturbed. The sap-tube system is then 
deficient and the cells suffer from a lack of water. (d) The 
disease is favored by alternating wet and dry weather. Fluc- 
tuating temperature and humidity near the ripening period are 
highly favorable to bitter-pit, and conversely as long as the 
water is regularly supplied to the fruit, or at least as quickly as 
it is lost by transpiration, there is no pitting. Dry weather 
suddenly followed by heavy rainfall results in the development 
of stippen on the tree. And excessive transpiration, such as 
occurs in warm, dry weather, with a light crop of fruit is favor- 
able to the disease. In other words, when transpiration is rela- 
tively greater than the water supply, stippen is produced. It 
is seen then that the weather conditions play a prominent réle 
