in chemical composition due to variations in growing conditions are so 
great that any picking test based on chemical composition has proved 
unsatisfactory. 
Many tests have been made to determine whether the disappearance 
of starch (determined by the iodine test) is an indication of maturity. 
There is a gradual conversion of starch to sugar as the fruit matures, 
but some varieties become mature before any appreciable change oc- 
curs in the starch test. Some starch always remains when the fruit 
is in the best condition for picking, but the extent of the conversion at 
maturity may vary with different climatic and cultural conditions. 
Thus, as with other chemical tests, those based on starch disappearance 
have but limited value in determining stage of maturity of apples. 
CorKING OveER OF LENTICELS 
The lenticels, or pores in the skin, which in the immature fruit open 
more or less directly to the flesh tissue below, become filled with cork 
cells and sealed partially or wholly as the fruit approaches maturity 
on thetree. The waxy coating also develops on the surface of the fruit 
during the latter part of the growing season. The development of the 
heavy wax coating and the sealing of the lenticels make the fruit that 
is well matured at picking time somewhat more resistant to wilting 
in storage than that picked in an immature condition. These changes, 
however, are not sufficiently discernible to make them of much value 
in determining when the fruit should be picked. 
CHANGE IN Fruir CoLor 
The change in color of apples as they mature on the tree is twofold. 
One is the development of red in blushed or colored varieties, while 
the other is the change in the unblushed portions. The green ground 
color of the immature fruit changes first to greenish yellow and 
finally to an almost full yellow as the fruit matures. 
The development of the red color is a very important factor in 
determining when to pick apples for commercial purposes, since high 
color is essential to the advantageous marketing of many varieties. 
The development of red depends very largely. however, upon the 
exposure of individual fruits to sunlight and upon the prevalence 
of bright, sunny days during the maturing season. The sugar con- 
tent of the fruit also appears to be an important factor in color 
development. Except in the early coloring sport strains, the develop- 
ment of a good red color is usually indicative of maturity. However, 
because of the variability in color development associated with 
weather conditions, fertilizer practices, and other factors, red de- 
velopment is not a fully dependable criterion of maturity. Some 
fruit may be mature before it is well colored, whereas other fruit, 
particularly that of colored strains, may be colored before it is 
mature. 
Light exposure has little to do with the disappearance of the green 
ground color in the unblushed parts of apples, and in some varieties 
this disappearance is a supplemental index of maturity. In the red 
bud sports of some varieties the red frequently covers the surface 
so completely and so early that the ground color cannot be observed. 
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