UNFRUITFULNESS ASSOCIATED WITH EXTERNAL FACTORS 517 



The following regarding weather conditions at blossoming time in New 

 York verifies this statement;*" "Wet weather almost wholly prevented the 

 setting of fruit in New York in the years 1881, 1882, 1883, 1886, 1890, 1892 and 

 1901. Rain is mentioned as one of the causes of a poor setting of fruit in the 

 years 1888, 1889, 1891, 1893, 1894, 1898, 1905. . . . Rain and the cold 

 and wind that usually accompanj' it at blossoming time cause the loss of more 

 fruit than any other cUmatal agencies. The damage is done in several ways. 

 The most obvious injury is the washing of the pollen from the anthers. The 

 secretion on the stigmas also is often washed away or becomes so diluted that the 

 pollen does not germinate. It is probable that the chill of rainy weather decreases 

 the vitaHty of the pollen and an excess of moisture often causes pollen grains to 

 swell and burst." 



Experimental evidence on the damaging influence of rain on fruit 

 setting is furnished by an experiment in which a Mount Vernon pear 

 tree was sprayed continuously for 219 hours while in bloom. ^^ This 

 tree set very little fruit while a tree of the same variety standing nearby 

 and not subjected to such treatment set a good crop. Similar results 

 were obtained with two Duchess grape vines. 



However, plants possess many protective devices which serve to 

 reduce injury to their blossoms from rain. Thus in Vaccinium and 

 many other genera the flower is pendent and the essential organs are 

 protected by a bell-shaped corolla; in Opuntia and many others the 

 petals close over stamens and stigma during damp weather; the male 

 racemes of the Juglandacese and Cupuliferse are pendulous and shed 

 water almost perfectly when mature and in Vitis anthers that have 

 dehisced and shed part of their pollen close and shut out water upon the 

 advent of rain." In the investigation just citied, it was found that 

 pollen of the Duchess grape when examined under the microscope 

 after 11 days of continuous spraying was apparently uninjured.'*^ Work 

 with the plum has shown conclusively that after pollination the pollen 

 is washed from the stigmas only with great difficulty and that stigmas 

 will secrete their fluid a second time if rain removes that first secreted. ^^ 

 Rain, however, is usually accompanied by temperatm-es below those 

 characterizing fair weather at the same season. Thus Hedrick in the 

 report just cited states that "rainfall came in periods of prolonged cold 

 weather in the years 1881, 1882, 1883, 1886, 1888, 1889, 1891, 1892, 1894, 

 1898, 1905. Frosts and cold weather accompanied the rains in 1888, 1889, 

 1890, 1891, and 1892." In the light of these and many other observa- 

 tions and findings as to the distinctly different effects of low temperature 

 on rate of pollen tube growth and time of style abscission, it may be 

 questioned if rain at blossoming is in itself a very important factor in 

 limiting the set of fruit. Other conditions, particularly lower tempera- 

 tures, with which rain is generally associated, and interference with the 

 work of pollen-carrying insects, are more important. This statement 



