Abscission of Flowers and Fruits of the Apple 105 



(Pfeffer, 1904), The formation of such a layer was induced by the follow- 

 ing means: (i) removing the fruit and leaving varying lengths of stem; 

 (2) coating the fruit with vaseline; and (3) submitting the fruit to htimid 

 atmospheric conditions. The effects of these various treatments are 

 given below. 



The observations recorded suggest that the formation of the absciss- 

 layer is associated with the inhibition of sap movement. So long as the 

 sap passes into the fruit, .as it does under normal conditions, or away from 

 it as is the case when the leaves draw the watery sap from the fruit, the 

 layer is not formed; but when the movement of sap ceases while the spur 

 is still active, as it does when the fruit is removed from the stem or when 

 transpiration is checked by coating the fruit with vaseline or by exposing 

 the fruit and the spur to humid conditions, the absciss-layer is produced 

 which brings about the shedding of the fruit or the stem. 



Effect oj removing fruit and leaving varying lengths oj stem 



A number of Maiden Blush fruits ranging from one to one and one-half 

 centimeters in diameter were cut from the stems in such a way that the 

 stem in each case remained attached to the spur. The length of the 

 stems remaining after the removal of the fruits varied. In some cases 

 the fruit was removed and the entire stem was allowed to remain on the 

 spur; in other cases the stem was shortened to half its original length. 

 The first experiment was performed on Jiuie 8, 191 5. Six days later the 

 short stems readily snapped from the spurs when touched and the long 

 stems adhered somewhat firmly, while stems that had fruits did not come 

 off when touched. Two days later the long stems from which the fruits 

 had been removed fell naturally. Repeated experiments gave similar 

 results. Removal of the fruit from the stem induced the formation of 

 the absciss-layer which resulted in the shedding of the stem. The shorter 

 the stem, the more quickly, apparently, was this layer formed. 



Effect of coating fruit with vaseline 



In connection with studies concerning aphid work, the entire fruit, 

 stem and all, was coated with vaseline. All fruits so treated fell within 

 a week, while uncoated apples remained attached. Subsequent experi- 

 ments regarding the influence of coating the fruit with vaseline gave 

 similar results. The same effect was obtained by coating the fruit with 

 grafting wax. The treated apples were apparently normal in all respects. 

 The effects of coating would be to inhibit transpiration and exchange 

 of gases. 



^19 



