50 Bulletin 393 



on the tree, and of those that are shed several weeks after blooming time, 

 have shown that fertilized as well as unfertilized fruits drop. Osterwalder 

 studied also the transpiration by the petals of the flowers. The amount 

 of water lost in this way was found to be much less than that given off 

 by a similar area of leaf surface. He believes that wilting of the floral 

 parts is more likely to result from the loss of water thru the leaves than 

 thru the petals. He holds that fruitfulness depends on nutrient con- 

 ditions, on the number of fertilized fruits, and on the tendency of the 

 variety to develop fruits parthenocarpically. 



Insects and diseases, chiefly codling moth and scab, are often mentioned 

 in literature as causing heavy drops of blossoms and immature fruit 

 (Bailey 1895, Reddick 191 2, Wallace 19 13). Too rapid vegetative growth, 

 especially of young trees, is sometimes cited as unfavorable to fruit setting 

 (Waite, 1894). A number of other general causes, such as poor soil, 

 plowing during blooming time (Gould, 1915), drought, and the like, 

 are occasionally held accountable for crop failure after blossoms have been 

 produced. 



MATERIAL USED IN THESE EXPERIMENTS 



The observations and experiments recorded in these pages were made 

 during the course of three summers, i9i4to 1916 inclusive. For' the most 

 part the work was done at the experiment station orchard at Ithaca, 

 New York, but observations on a few outlying orchards in western New 

 York were also made. Unless otherwise mentioned, the trees under 

 observation were between forty and fifty years old. About seven years 

 ago these trees were pruned severely, and since that time they have received 

 ordinary care — that is, cultivation, pruning, and thoro spraying. 



In this paper the natural drop only is considered, not the drop caused 

 by such external agents as frost, insects, and diseases. In a well-sprayed 

 orchard the drop resulting from scab and from codling moth is practically 

 negligible. Examination of several hundred flowers and small fruits 

 collected from sheets suspended under the trees in the station orchard 

 at Ithaca in the spring of 19 16, showed that only about one per cent 

 were affected by scab. In western New York, however, the unfavorable 

 weather did not permit the growers to spray effectively that spring, 

 and, as a result, scab infection on the stems of flowers and young fruits 

 caused a heavy drop. Cases of a similar nature have been reported 

 previously (Bailey 1895, Reddick 1912, Wallace 1913). 



MAGNITUDE OF THE FIRST AND OF THE JUNE DROP 



Before any experimental work was undertaken, a detailed survey 

 was made of the extent and distribution of the first drop and of the June 



164 



