APPLE DISEASES 31 



(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. 



