Jan. 5, 1924 
Physiological Studies on Apples in Storage 
11 
of the fruit, since it results in the cells being ruptured when pressure is 
applied, rather than simply separating. As the cementing material is 
hydrolized, the cell walls tend to separate more and more readily and the 
fruit becomes progressively softer. This fact also probably,explains the 
juiciness of green apples, and the apparent lack of juice in the soft or 
mellow fruit. The juice is primarily within the cells, and escapes only 
when the cell walls are broken. If the cells can separate readily, the 
individual cell walls will not be broken to an appreciable extent when the 
fruit is crushed. Consequently the soft or “mealy” fruit also appears 
“dry,” although actually containing practically as much moisture as 
when hard. This apparent dryness may also be caused in part by the 
greater absorption of water by the cell colloids as the fruit softens. 
As the fruit ripens, both on the tree and in storage, these changes in 
pectin materials go on. It has not been established how far they 
progress, but it is often asserted in the literature that the “pectin 
decreases as the fruit ripens.” This usually has referred to pectin ex¬ 
tracted by boiling water, and would include both “pectin” and calcium 
pectate or “pectose.” This would indicate that as the fruit ripens and 
softens hydrolysis may go so far that some of the pectin materials will 
break down to sugars. The sugars of the fruit may thus be very slowly 
augmented throughout the life of the apple. Because of the complexity 
of the compounds involved and the large quantities of various sugars 
always present in fruit tissue, these points are very difficult to establish. 
summary of changes in the fruit while on the tree 
The changes associated with growth and ripening may then be sum¬ 
marized as follows: There is a continuous increase in size of the fruit 
from blossoming time until late season. This increase will vary greatly 
with growing conditions. Growth in size is accompanied by changes in 
the skin, the wax being formed during the latter part of the growing 
season, and the lenticels being corked over. Associated with these 
changes are color changes. Red pigment may develop just below the 
epidermis on fruits exposed to sunlight. The green color gradually 
gives way to yellowish green or yellow as the chlorophyll disappears. 
The fruit softens as it ripens, the rate of softening also undoubtedly 
varying with growing conditions. Associated with all these physical 
changes, there is a gradual decrease in acidity and an increase in sugars 
as the fruit ripens. Starch during the late growing season gradually 
changes over to sugar. Changes in the pectin constituent of the cell 
walls, consisting probably in insoluble calcium pectate being changed to 
water-soluble pectin or pectic acid, allows the cells to separate and 
break more readily and results in a softening of the fruit. 
CHANGES IN APPLES FOLLOWING THEIR REMOVAL FROM THE TREE 
The removing of fruit from the tree entirely stops certain of the proc¬ 
esses going on in the fruit, while others continue in much the same 
manner as though the fruit remained on the tree. Increase in size 
stops, as well as development of red color. The latter is probably due 
to the removal from direct exposure to light rather than to the cutting 
off of any substance derived from the tree. The green color of the 
unblushed surface continues to disappear, and the yellow color, pre¬ 
viously masked by the green, becomes predominant. It is not known 
whether or not any changes in the epidermal covering occur following 
