junei6, I9I9 Relation of Weather to Fruitfulness in Plum 105 



being the point Goff (5) found that plum pollen did not germinate and 

 the latter the temperature of slow tube growth. 



Since the weather at the Fruit-Breeding Farm has not been recorded, 

 this analysis is made from the records furnished by Mr. U. G. Purssell, 

 of the United States Weather Bureau, at Minneapolis. 



EFFECT OF UNFAVORABLE WEATHER ON THE SETTING OF FRUIT 



It has been a matter of common observation among fruit growers that 

 when the blooming period is accompanied by a prolonged rain there is 

 generally a light setting of fruit. Halsted (d), in an attempt to deter- 

 mine the cause of this, performed an experim.ent in which an apple tree 

 was kept wet with a spray of water for six days while in bloom. The 

 weather was fair during the experiment. The sprayed tree failed to set 

 any fruit, except in a few instances on the upper branches, while the 

 surrounding trees of the same variety set full. 



Beach and Fairchild (j) performed a similar experiment with a Mount 

 Vernon pear tree and a Duchess grapevine. The pear tree subjected to 

 a spray for nine days bore a single fruit. Pollen taken from "fresh 

 anthers" on the fifth day and placed in a sugar solution proved to be 

 "perfectly capable" of germination. Many of the stigmas examined 24 

 hours after the experiment began were found to be "dusted with pollen," 

 although no insects had been seen near the tree. After the close of the 

 experiment many anthers opened and shed an abundance of pollen. 



In the case of the Duchess grape, although the 12 days' treatment did 

 not cover the entire period of bloom, the treated vines bore many aborted 

 berries, but on none of the clusters were all of the berries aborted. Also, 

 the average size of the fruit was reduced approximately one-half. 



In these experiments the conditions which generally accompany a pro- 

 longed rain were not duplicated exactly, and consequently other factors 

 may have entered into the results obtained. However, a constant spray 

 was effective in preventing fruitfulness in the apple and pear, and even 

 in the case of the grape sufficient pollination to account for the setting of 

 fruit which took place may have occurred after the water was turned off. 



It will be of interest here, after a review of the experiments of Halsted 

 (6) and of Beach and Fairchild {3), to include a statement concerning the 

 percentage of fruit to set in a plot of Surprise seedlings at the University 

 Farm in order to show the general effect of unfavorable weather. All 

 trees bloomed heavily during the seasons of 191 7 and 191 8 and for this 

 reason present an excellent illustration of the effect of weather upon the 

 setting of fruit. These seedlings are about 13 years old, fairly uniform 

 in size, and are growing under clean cultivation. It would appear that 

 ample pollination would take place if the weather were favorable, be- 

 cause these seedlings are located within less than a quarter of a mile of 

 the University apiary of about 100 colonics. In general it may be 



