520 FUNDAMENTALS OF FRUIT PRODUCTION 



Other Factors that Cause the Dropping of Fruit and Flowers. — Many 

 other agencies besides those mentioned may occasionally cause flowers or 

 developing fruits to drop prematurely. Among these may be mentioned 

 the presence of small amounts of illuminating gas in the atmosphere.^* 



BushnelP^ has found that fruit setting in certain cucurbitaceous 

 plants is characterized by a distinct periodicity. That is, flowers 

 opening during a 2- or 3-day period may set freely, those opening 

 during the next 2 or 3 days set poorly, then there is another period of 

 good setting and so on. 



Summary. — The most important of the direct effects of the environ- 

 ment through the plant itself is in influencing nutritive conditions. 

 Soil type, water supply, fertilizers, cultivation and pruning are more 

 or less important in this connection. Low temperature and rain are the 

 two most important of the environmental factors indirectly affecting 

 fruit setting through affording or preventing the opportunity for pollina- 

 tion, the germination of the pollen grain and fertilization. 



It is evident from the subject matter presented in this and the two 

 preceding chapters that the whole subject of fruit setting is complex. 

 In the first place it depends on a number of internal factors, many of 

 which are entirely beyond any direct or indirect control. Secondly, 

 blossoming generally comes at a season when great fluctuations in 

 temperature, humidity and the other features of environment are likely. 

 It is therefore not surprising that the response of the tree to the combina- 

 tion of all these interrelated factors and conditions varies from year 

 to year, from orchard to orchard and even from tree to tree. It is 

 fortunate indeed for the grower that the most important of the limiting 

 factors to fruit setting — both those internal and those external to the 

 plant — are within the grower's control by either direct or indirect means. 



