32 MANUAL OF FRUIT DISEASES 
(6) Factors having to do with transpiration are concerned in 
the cause of stippen. 
(7) Intermittent weather conditions favor the development 
of the disease. A light crop of poorly distributed fruit is most 
liable to bitter-pit. 
(8) Fluctuating temperature and humidity in storage favors 
the disease. Uniform, low temperature and dry air are inim- 
ical to it. 
It is then apparent that growers should everywhere be on 
guard against this disease. No one can safely assume that his 
fruit will always escape by virtue of the variety which he grows 
or of the locality in which it is produced. It is very important 
that everything possible be done which will tend toward the 
production of good crops evenly distributed over the tree 
year after year; for herein lies a possible solution of the control 
of stippen. Most growers know that vegetative growth is un- 
favorable to fruitfulness. On the other hand, injudicious, heavy 
pruning to eliminate the vegetative growth also favors bitter- 
pit. It is believed that above all other orchard operations 
pruning has the most direct effect on the development of 
stippen. For it may regulate the amount, and to a certain 
extent the size, and it may determine the distribution of the 
fruit on the tree. The system adopted should be carefully 
planned, it should aim at the production of a regular crop of 
evenly distributed fruit, and should therefore be light. The 
lateral system of pruning, that is, the retention of laterals, as 
far as practicable, is to be adopted as a part of the general 
pruning-scheme, particularly in the case of varieties most sus- 
ceptible to the disease. For there is some evidence that bitter- 
pit is much reduced on trees when the fruit is borne on lateral 
rather than on main branches. Frost at setting is also unfa- 
-vorable to fruitfulness, therefore the question of frost-protection 
should receive attention in localities where experience has 
proved its necessity. Regulated sap-flow favors fruitfulness, 
