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 role 



