486 FUNDAMENTALS OF FRUIT PRODUCTION 



forms between the second and third drops as well as between the first and second. 

 In approximately one month the second drop is over, and those setting have so 

 increased in size as to place them in a distinct size class from those which have 

 fallen. . . . 



"Sections have been made of the embryos of a large number of plums which 

 fell at the June drop. Dissections were also made of ovules at various stages to 

 determine the amount of growth in the embryo. The general condition found 

 may be summarized as follows: (a) embryo development started but growth 

 stopped at any time from the stage when the embryo was a few cells across to 

 the time at which it had reached nearly the mature size; (b) endosperm had partly 

 formed, but the embryo gained the ascendency to such an extent that it was 

 often found naked in the nucellus ; (c) enlargement in the seed could reach nearly 

 the mature size when fertilization had once occurred, accompanied by only a 

 sUght growth of the embryo. . . . 



"The status of development in the ovule in the third drop shows marked 

 differences from that in the second. Firstly, greater size is attained than is ever 

 found in the second drop, and secondly, instead of there being disintegrating 

 nuclei within a slightly elongated embryo sac, tissues cease growing at various 

 stages rather than disintegrating. This latter fact alone suggests an additional 

 stimulus absent in the second drop. ..." 



It is not known exactly how many other fruits have three distinct 

 periods in which blossoms and developing fruits drop. However, the 

 sweet cherry has three such periods; some varieties, at least, of the apple 

 and pear have corresponding periods and presumably they are to be found 

 in a number of other fruits, though in some of these species or varieties 

 they may be associated with other internal and environmental condi- 

 tions. Certain other fruits, such as the currant and the raspberry 

 show quite different characteristics in their fruit setting and fruit drop- 

 ping. In some, as the strawberry, the flowers either set fruit or fail to set 

 and there is no later dropping or abortion. However, the so-called "June 

 drop," which may or may not occur in June and may correspond either to 

 the second or the third drop of the plum is important in determining the 

 size of the crop with most deciduous tree fruits. 



Usually, though not always, the relation between the losses incident 

 to the successive drops varies with the severity of any one of them. 

 Heinicke''^ points out that when the "first" drop in the apple is relatively 

 large the June drop is relatively small; on the other hand the June drop 

 is heavy if a comparatively large proportion of the flowers begin to form 

 fruits. This may vary according to variety or with the conditions under 

 which it is grown. Comparable to this is the condition pointed out by 

 Reed^*" in certain lemon varieties, in which an individual flower bud on 

 a small inflorescence has a greater chance to set and develop into a mature 

 fruit than one on a large inflorescence. Napoleon is an example of a 

 sweet cherry variety that, as grown in the Pacific northwest, almost 

 invariably shows a heavy first drop, a light to heavy second drop. 



