516 FUNDAMENTALS OF FRUIT PRODUCTION 



mates the fruiting of the male is rare. It is to be remembered in this connection 

 that all the staminate flowers of the male trees possess an undeveloped or an 

 abortive pistil. The only change in the cases mentioned consists in the develop- 

 ment of this pistil." 



Light. — It is doubtful if variations in light supply are important 

 with deciduous fruits. However, it is of some interest that the willow- 

 herb (Epilobiu7n angustifolium) develops its flowers normally and sets 

 fruit and seed freely in open sunny situations but when shaded its flower 

 buds abort and fall off before opening. ^^ In fact, this is true of many 

 plants. 



Disturbed Water Relations. — In the section on Water Relations 

 it is shown that conditions of low atmospheric humidity, high tempera- 

 ture, exposure to high winds and a limited supply of soil moisture some- 

 times induce in trees moisture deficits that lead to the formation of an 

 abscission layer and the dropping of the blossoms or fruits. The water 

 loss in developing Washington Navel orange fruits at and shortly after 

 midday has been shown to be as much as 30 per cent.^^ Practically the 

 same conditions have been found responsible for much of the shedding 

 of the developing bolls in cotton.*^ Studies of boll abscission in cotton, 

 however, led to the conclusion that the water deficit in the leaves and 

 stems was only indirectly the cause of abscission since the water deficit 

 produced in the tissues a rise in temperature which was "the stimulus 

 which directly leads to abscission." 



The dropping of flowers or partly developed fruits that is due to 

 water deficits is partly under control. Irrigation, tillage, the use of 

 certain cover crops and windbreaks are among the more important 

 means that tend to lessen the difference between absorption and trans- 

 piration in times of stress. 



Discussing the shedding of cotton balls because of water deficits Floyd ex- 

 plains how a surplus of water may act in the same way. He says: 



"If the general conclusion that the grand march of shedding is due to the 

 depletion of moisture in the deeper soil be true, irrigation and better soil manipu- 

 lation are indicated as remedies. It has been shown experimentally by Barre, 

 in South Carolina, that irrigation has the effect of inhibiting shedding. The 

 observations of Balls that the rise of the water table in Egypt due to the Nile 

 floods, by asphyxiating the deeper roots and so limiting the water supply, causes 

 severe shedding, are quite in harmony with the above findings, since too much 

 water may have quite the same effect as too little, and suitable drainage is thereby 

 indicated as surely as irrigation. "^^ 



Not only may a water deficit lead to the dropping of flowers and newly 

 set fruits, but it has been shown experimentally that very high atmos- 

 pheric humidity tends to cause the abscission of partly developed apples.^' 



Rain at Blossoming. — Rain at blossoming is recognized generally 

 as one of the most important factors Umiting the set of fruit. 



