30 MANUAL OF FRUIT DISEASES 



in causing this disease while the fruit is still on the tree. On the 

 other hand, the methods of orchard management are contrib- 

 uting factors not to be overlooked. Heavy pruning is thought 

 to favor the disease, for pruning affects transpiration. When 

 the balance between the portions of a tree above ground and 

 the roots under ground is disturbed, injury is likely to result. 

 The application of manures not only supplies food but modifies 

 transpiration. Green-manures conserve moisture in the soil. 

 Manures of any kind invigorate the tree and enable it to use 

 water from the soil in a more economical fashion. Cultivation 

 conserves moisture and affects transpiration in a manner favor- 

 able to the tree. Irrigation must be taken into account. 

 Regular and continuous growth is inimical to the development 

 of bitter-pit. But if water is applied through irrigation in an 

 injudicious fashion, conditions are made favorable to the disease. 

 The disease also develops in storage. It has been found that 

 fruit apparently clean when picked will show stippen after a 

 considerable period in storage. Conditions in storage favor- 

 able to the disease are similar to those favoring it on the tree. 

 Fluctuating temperature and humidity combined are evidently 

 responsible for the production of bitter-pit. On the other 

 hand, a uniform, low temperature and a dry air are unfavor- 

 able to the disease. 



(2) The second theory brought forward to explain the cause 

 of stippen is that the injury is due to excessive transpiration 

 of water from the fruit during warm days followed by reduced 

 transpiration during the cool nights. A warm day results in 

 rapid absorption of water by the roots and in its rapid loss by 

 transpiration. The ensuing cool night checks the elimination 

 process, but the soil remaining warm allows the roots to go on 

 pumping water into the tissues of the fruit. This results in 

 an internal pressure which finally bursts the distended cells. 

 They soon die and turn brown, and give rise to the symptoms 

 of stippen. 



