THE RELATION OF CLIMATE TO POMOLOGY 221 



191. Rainfall. — The rainfall situation is indicated for 

 the larger districts under paragraph 199. Most sections are 

 likely to suffer at times from droughty conditions but a 

 large part of the United States is well supplied with rainfall. 

 The distribution of the rainfall throughout the twelve 

 months has much to do with its efficacy in crop production, 

 for even though a heavy annual rainfall is recorded for a 

 region, it will avail little if a large proportion of it falls in 

 the non-growing period. 



Rain at the blossoming period of fruit-trees is particularly 

 injurious to the crop from both direct and indirect causes. 

 It is primarily injurious because it prevents pollination, es- 

 pecially when the rain is accompanied by cold weather and 

 gales of wind. Injury to the floral parts may result from 

 such weather conditions, but more particularly the insects 

 instrumental in effecting pollination are not active. In the 

 twenty-five years between 1881 to 1905, inclusive, Hedrick 

 reports fourteen seasons in which rain or snow at blossom 

 time was destructive or partially so to the fruit crop in some 

 sections of New York state. ^ The effect of such inclement 

 weather is probably more pronounced with self-sterile 

 varieties of fruits than with the self-fertile ones. 



According to the investigations of Dorsey, rain operates 

 against poUination and fruit-setting by causing the anthers 

 to close or by preventing them from opening, but it does 

 not burst the pollen-grains nor kill them. Neither does 

 rain wash pollen from the stigmas to any great extent as 

 has been reported, since there is a strong adhesive action 

 between stigmas and pollen. In general, however, no fac- 

 tors of weather are so effective in preventing the setting of 

 fruit as rain and low temperatures.- 



1 N. Y. (Geneva) Agr. Exp. Sta. Bull. 407. 1915. 

 -Dorsey, M. J. Relation of weather to fruitfulness in the plum. 

 Jour. Agr. Res., Vol. 17, No. 3. 1919. 



