no Journal of Agricultural Research voi. xvii. no. 3 



fly from the hive until the temperature is about 60° F. unless they are inpelled to fly 

 by a long period of confinement resulting in an accumulation of feces. ^ 



The minimum temperature curves in Plate 15 show that there are 

 only relatively short intervals when the temperature is below 50° F. 

 It would appear that if bees were present in sufficient numbers, other 

 conditions being suitable, ample pollination would undoubtedly take 

 place, at even short intervals of favorable weather. 



SUNSHINE 



Sandsten {14) showed that while sunshine had a direct influence upon 

 fertilization in the tomato, it had none in the plum. Judging from his 

 experiments, sunshine appears to have its chief bearing in this connection 

 upon such factors as insect flight and general plant activity, particularly 

 nectar secretion. Kenoyer states {10, p. 21) that "clear days are 

 preeminently the days for honey production." From general observa- 

 tion of bee activity on plum bloom, the same may be said regarding 

 pollination. As will be seen later, however, pollen is most readily avail- 

 able for dissemination in dry, sunny weather when bees are most active. 



The total hours of sunshine during blooming are less than might be 

 expected. The character of the day is indicated in Plate 15 at the base 

 of the graph for each year by the shading. For the 7-year period there 

 has been, while plums were in bloom, an average of only 49 hours of 

 sunshine each season, compared with an average of 56 hours of cloudiness. 

 The minimum was reached in 191 6, when there were only 27 hours of 

 sunshine. Alone, however, the absence of sunshine does not prohibit 

 the setting of fruit. 



RAIN 



On account of the nature of the processes taking place at blooming 

 time, rain has the most immediate action of all of the factors of weather. 

 The fact that the period of pollination is so limited in the plum makes 

 it possible for rain to delay normal functioning to an injurious extent. 

 Furthermore, the stigma is exposed to weather during the limited time 

 it functions. It will be seen, therefore, that rain may influence processes 

 which, on account of the structure of the organs concerned, must function 

 when more or less exposed. 



EFFECT OF RAIN UPON DEmSCENCE 



A study of the bloom in the orchard during a heavy and prolonged 

 rain showed that the stamens were drawn together and held in a cluster 

 about the pistil by a large drop of water. This was typically the con- 

 dition in the absence of wind and in protected locations. The added 

 weight of water held in this way resulted in a drooping of the branches, 



» Personal correspondence with E. F- Phillips of the U. S. Department of Agriculture, Bureau of Ento- 

 mology, Dec. 26, 1918. 



