APPLE DISEASES e 33 
(3) A third theory is based on the assumption that the 
disease is most destructive in dry seasons. The premature 
dryness of the soil results in a failure of sufficient mineral food 
to reach the fruit, in consequence of which certain groups of 
cells starve and perish. 
Many other causes have been assigned to stippen. Among 
the more prominent ones may be noted: local poisoning by 
spray material, poisons absorbed by the roots, bacteria, fungi, 
insects, mechanical injury, unfavorable grafting, degeneration 
from old age, and finally a peculiarity of the variety. A dis- 
cussion of these various factors as causes of bitter-pit seems out 
of place in the present state of knowledge regarding the disease. 
None of them is known to be either direct or contributory 
causes of stippen. 
Control of bitter-pit. 
From the foregoing statements the following facts regarding 
bitter-pit are to be considered in discussing control : 
(1) The disease has a very general geographical range. 
(2) Some varieties of apples are more susceptible than others, 
although probably none is immune. 
(3) The history of the disease indicates that it frequently 
becomes a serious problem to the apple-grower. 
(4) The fruit only is affected and it usually shows the disease 
at the approach of maturity on the tree, or in storage. 
(5) The disease develops beneath the skin at points near the 
sap tubes. This close proximity has suggested to the minds of 
those investigating the disease that stippen is in some way 
connected with the water supply of the fruit. Prominent 
authorities agree that a deficiency in the water-supply gives 
rise to the difficulty. Either the water is lacking in the soil, 
or it is eliminated from the fruit before certain cells have re- 
ceived their necessary quota. This results in sap concentra- 
tion, chiefly an increased acidity within the cell, and the living 
substance is killed. 
