368 



Bulletin 181. 



theless it is interesting to know in what way rain decreases the setting 

 of fruit. 



If a rain comes while the trees are in full bloom the pollen is 

 washed from those anthers which hav^e already opened, and is thus 

 prevented from reaching the stigma. Should the rain be a short 

 one, no serious harm need result from this loss of pollen, for tlie 

 unopened anthers will burst and pollination will begin again soon 

 after the sun comes out. The washing away of pollen has very lit- 

 tle influence in decreasing the setting of fruit, particularly when the 

 rain is short. There will generally be enough pollen to supply the 

 pistils before or after the rain. 



The poor setting of fruit which often follows a long rain and 

 sometimes a shower is due more to a loss of vitality in the pollen or 

 to some mechanical injury to the pistils; also, in large measure, to 

 the fact that bees and other insects which promote the beneficial 

 cross-pollination between varieties are absent. If the rain lasts for 

 several days, the pollen may lose its vitality. After a week of rainy 



weather at Itiiaca in the spring of 1898, 

 nearly all the pollen of the apricots then 

 in bloom was disorganized and stuck 

 together, so that it could not possibly 

 grow and fertilize the pistils. St)me of 

 this pollen is shown in Fig. 78. It is 

 also natural to suppose that a hard rain 

 1%. — Pollen injured h\i rain, may wash off, dilute, or otherwise injure 



the juices of the stigma so that the pol- 

 len cannot germinate after it fallls 

 upon the stigma. Perhaps a long "spell" of wet weather may 

 even kill the pistils after they have been fertilized. 



Thus a rain during the. blooming season may decrease the setting 

 of fruit in four ways : (1) By preventing the pollen from reaching 

 the stigma, both because it is too wet to fly and because pollen- 

 carrying insects are absent. This is important only when the rain 

 lasts several days and most of the pistils pass their receptive state 

 before the rain ceases. (2) By destroying the vitality of the pollen. 

 (3) By injuring the stigma. (4) By preventing fertilization or the 

 germination of the pollen l)eeause of low temperature. 



— Pollen injured by rain. 

 Much magnified. Compare 

 Fig. 80. 



