252 The Commercial Apple Industry 



bloom profusely the blossoms are so weak that they fail to 

 set fruit. 



5. Winter-injury to fruit-buds may occur. The apple 

 ordinarily does not suffer greatly from winter-killing of 

 fruit-buds. In the case of most varieties, the fruit-buds 

 are no more sensitive to winter-killing than the tree itself. 

 However, the vitality of the buds may unquestionably be 

 affected by the character of the winter, particularly if the 

 relative humidity is low. Dry atmosphere and soil are 

 more often the cause of injury to fruit-buds than extreme 

 cold. 



6. The buds or bloom may be injured by late spring 

 frosts. Often buds are injured by frost before bloom and 

 if not killed outright are so weakened as to be unable to 

 set fruit. Fortunately, when freezes occur before bloom, 

 there are usually some buds which are not so far advanced 

 as^ others and which for this reason escape injury. Severe 

 killing frosts are those which occur when the trees are in 

 full bloom or just as the bloom is being shed. Frost at 

 this time may so impair the fruiting organs as to cause 

 dropping of the fruit after it has once set. / 



7. Some varieties have an inherent inability td set fruit, 

 although grown under favorable conditions and blooming 

 profusely. These varieties are more frequently home 

 orchard sorts and seldom trouble the commercial orchardist. 



8. The last and one of the most important factors which 

 affect the proper set of fruit is pollination. Proper pol- 

 lination is usually dependent on one or some combination 

 of six different factors: (a) In the case of self-sterile or 

 partially self-sterile varieties, proper pollination can not 

 take place unless other suitable varieties are present for 

 pollinizers. (b) An absence of insects or other agents 



