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. 
