Jan. 5 1924 
Physiological Studies on Apples in Storage 
5 
Zschokke found the stomata ruptured before the cork cells had formed, 
in which case protection was provided by the drying down of the under¬ 
lying tissue. This, however, afforded opportunity for the entrance of 
microorganisms. 
The epidermal covering of the apple consists of a cuticle, or wax coating 
on the outside, a layer of thick-walled epidermal cells, and below this a 
subepidermal region, consisting of a number of layers of thick-walled 
small and compact cells. The cells of the subepidermal region gradually 
become larger as the distance from the epidermis increases. The pig¬ 
ment, both red and green, is contained primarily in these subepidermal 
cells. 
There apparently is a progressive thickening, not only of the cuticle, 
but of the subepidermal area as well, as the season progresses. Zschokke 
found a distinct variation in the thickness of these regions with the expo¬ 
sure of the fruit to the sun as well as with the variety. The writers have 
noted a distinct variation in the thickness of the subepidermal region 
upon the blushed and the unblushed sides of the same fruit, heavily 
blushed sides of Rome Beauty showing 8 to 10 cell layers in this region, 
whereas the unblushed sides showed about 6 layers. 
The storage quality of fruits is undoubtedly closely associated with skin 
condition. Not only is the skin condition important in determining the 
amount of wilting in storage but it is of primary importance in determin¬ 
ing the resistance of the fruit to decay. The development of storage 
scald and other physiological troubles is also closely associated with skin 
condition. Cummings and Lombard (9), in a limited study, found an 
apparent association between thickness of the cuticular layer as a variety 
characteristic and keeping quality in apples. Perry and Martin ( 23 ) 
report a similar correlation. Practical fruit handlers have long judged 
the keeping quality of apples partially by the amount of wax present on 
them. There is much need for a more exact study of the effect of cli¬ 
matic factors upon the epidermal covering of fruits in order to judge more 
accurately the effect of these conditions upon the storage life of the fruit. 
The skin of the fruit as a whole is extremely important, not only as a me¬ 
chanical protection for the tissues beneath, but also as a partial regulator 
of the actual physiological processes going on in the fruit. This latter is 
accomplished through the action of the skin in limiting gaseous exchange. 
THU SOFTENING OF APPLES ON THE TREE 
There is probably no test so universally employed to determine the ma¬ 
turity of fruit as the resistance of the flesh of the fruit to pressure as esti¬ 
mated by pressing the fruit with the thumb. Lewis, Mumeek, and Cate 
( 18 ) used a mechanical tester to measure the rate of softening of pears on 
the tree. They found the fruit to soften rather rapidly, resistance to 
pressure decreasing at a rate of approximately 2 per cent per day. 
Apples are usually removed from the tree when in a “hard ripe” condi¬ 
tion. Color, ease of separation from the tree, amount of dropping, color 
of seeds, etc., as well as the softness of the fruit, are used to determine 
the time of picking. Notwithstanding the fact that apples are usually 
picked when “hard ripe,” there is in most varieties a very considerable 
softening of the fruit before its removal from the tree. The rate of this 
softening has been determined by means of a mechanical pressure tester 
similar in design to that described by Murneek ( 21 ). 
