THE McINTOSH DROP 5 



Difference in Varieties 



Dropping of apples is a natural phenomenon. But it interferes with full color 

 and qualit}' development more seriously with some varieties than with others. 

 Many varieties ripening in late summer and early fall may drop excessively, 

 while some late sorts hang on tenaciously. For example, Williams, Gravenstein, 

 Wealthy, Fameuse, and Mcintosh are worse offenders than Cortland, Rome 

 Beauty, Twenty Ounce, Northern Spy, and Golden Delicious. Length and 

 flexibility of pedicel and spur probably have some influence. For example. Golden 

 Delicious has a long pedicel and Rome Beauty a pendulous spur, both of which 

 tend to lessen the strain at the point of attachment of pedicel and spur. Mcintosh 

 has a rather short pedicel and a stiff spur which invite disaster during windy periods 

 at harvest time. , 



The Process of Abscission 



Morphologically, abscission is the severing of a modified branch or axis. It 

 may occur at various times from petal fall to harvest. But the nature of the 

 abscission process is not the same for flowers and young fruits as for older fruits. 

 According to observations of Heinicke (8), MacDaniels (15, 16), and McCown 

 (17), in early abscission, secondary cell division forms an abscission layer in or 

 somewhat distal to the abscission zone and separation occurs between cells in the 

 distal half of the abscission layer. But from the time of the completion of the 

 June drop and continuing to harvest, there is definite evidence that cell division 

 does not take place preceding or during abscission of maturing fruits. Rather, 

 the cause of cell separation lies in physiological and chemical changes such as 

 swelling and extension of cell walls and the breakdown of cellulose and pectic 

 compounds. MacDaniels (15) observed various modifications of the normal 

 pedicel in the region of the abscission zone which naturally weaken it in that area, 

 although McCown (17) concluded that the line of abscission does not invariably 

 keep within the zone bounds. Compared with Rome, Spy, and Delicious, the 

 abscission zone in Mcintosh is more clearly defined and relatively free from 

 sclerenchyma, fibers, and stone cells, and the constriction is deep, resulting in a 

 small cross-sectional area for support according to MacDaniels (15). No marked 

 structural differences could be found in the abscission zones of fruits from Mcin- 

 tosh trees showing differences in time of fruit dropping, however. McCown (17) 

 observed that pith abscission usually preceded the separation of cortical tissues 

 in Mcintosh and Grimes Golden while the reverse was true with Golden Delicious 

 and usually with Rome Beauty and Delicious. The latter procedure allows the 

 woody cylinder to hold the fruit for some time after the separation of the softer 

 tissues. He concluded that this variation in the mode of separation may account 

 in part for the variable severity of drop in different varieties. 



Some Apparent Causes of Drop 



There has been much fruitful investigation concerning the causes of the shedding 

 of flowers and the abscission of young fruits. Many factors, including fertiliza- 

 tion, embryo abortion, and competition have been evaluated. Comparatively little 



