Smock et al. (64) found that N°-benzyladenine stimulated respiration in the 
preclimacteric phase and depressed it about 10 percent in the postclimacteric 
period. No beneficial effects on the storage behavior was noted in the varie- 
ties studied. 
Ethylene 
The production of ethylene appears to be closely related to the climac- 
teric, but its exact role remains obscure. Burg (6) has comprehensively re- 
viewed the physiology of ethylene formation and its action in plant tissues and 
concludes that it participates as a hormone, stimulating ripening in perhaps 
all fruits. Biale (3) states that a climacteric induced by adding ethylene 
does not increase rates of respiration for the corresponding stages of the cli- 
macteric but merely shifts the time axis, 
The temperature of apples at the time of ethylene treatment has consider- 
able influence on the response. Fidler (15) found very little difference in 
untreated and treated apples during storage at 3° C. (37.4° F.). However, at 
storage temperatures of 7° and 12.5° C. (44.6 and 54.7° F.) the climacteric was 
induced earlier in ethylene-treated fruit. Gerhardt and Siegelman (16) measured 
the respiration, firmness, and soluble solids of apples stored at three temper- 
atures (31°, 45° and 65° F.) and did not find any differences between those 
ventilated with fresh air and those exposed to emanations including ethylenic 
and nonethylenic volatiles of ripening apples. Very high levels of ethylene 
accumulate in controlled atmosphere storages (15, 59). Either ethylene has no 
effect on ripening under these conditions, or the effect is far outweighed by 
the modification of the oxygen and carbon dioxide content of the atmosphere 
surrounding the apples. Wilkinson (81) suggests that a separation of the cli- 
macteric and ethylene production, which are usually considered to be coincident, 
can be brought about by delaying harvesting until the fruit are in their climac- 
teric on the tree. Under these conditions the ethylene production was found to 
lag considerably behind the rise in respiration. 
Attempts have been made to determine the origin of ethylene in apple 
tissues, Burg and Thimann (8, 9) have studied the effect of various solutions 
and inhibitors on ethylene production of apple slices. They have also found 
that the application of labeled glucose to the slices is followed quickly by 
the appearance of labeled carbon dioxide and, after a slight lag, by labeled 
ethylene. Burg and Burg (7) found that apple tissue could convert labeled 
triose into ethylene, but the efficiency was unexpectedly low in comparison to 
glucose. These and other studies led to the suggestion that ethylene may be 
produced by mitochondria or cytoplasmic particles. Lieberman and Craft (46) 
isolated cytoplasmic particles from apples that produced a gas which was later 
identified as ethane (45). 
Other Factors Affecting Ripening 
A number of factors could be discussed in detail here, but many of them 
are closely related to maturity and have been covered under the section of this 
review dealing with maturity. Fertilizers have been given wide consideration 
in their effect on maturity and ripening. In general, increasing levels of 
nitrogen result in fruit with less red and yellow ground color that are softer 
at harvest and after storage and respire at a higher rate (13, 67, p.1). Work 
Mes) 
