io * Journal of Agricultural Research voi. xxvn, no. i 
amount of sucrose present, as well as an increase in reducing sugar. In 
some varieties at the end of the growing season the quantity of reducing 
sugar and of sucrose was approximately equal, while in others the reduc¬ 
ing sugar was approximately double the sucrose in quantity. 
The starch content of the fruit, in terms of per cent of the green weight, 
reached its highest point in the summer varieties in June and in the 
winter varieties in July. The actual total quantity of the starch per 
apple, however, did not reach its maximum until much later, about 
mid August, in the winter varieties. From this time forward there was 
a decrease not only in percentage composition of starch but in actual 
starch per apple, indicating that there was an actual starch hydrolysis 
going on after this date. With starch hydrolysis there is a sharp increase 
in sucrose, indicating that the sugar storage form which replaces the 
starch storage as the fruit matures is primarily sucrose. 
CHANGES IN THE PECTIN MATERIALS 
There is much confusion regarding the changes that occur in the pectin 
materials during the ripening processes of fruits. The voluminous work 
on pectins has been admirably reviewed by Bigelow, Gore, and Howard ( 2 ) 
and need not be repeated here. Because of the probable intimate asso¬ 
ciation of changes in the pectin materials with the very important soften¬ 
ing of the fruit in storage, however, a brief summary of these changes is 
desirable. 
It is apparent that there is a water-insoluble pectin compound which 
acts as a cementing material in green fruit, as well as in other fleshy plant 
tissue. The exact chemical nature of this substance is not established, 
and it has been mentioned in the literature under various names, as 
pectose, pecto-cellulose, and calcium pectate. The more recent work 
indicates that this substance is calcium pectate. This calcium pectate 
cements the cell walls of the green fruit flesh firmly together, and is 
largely responsible for the “hardness” of green fruit, since such fruits 
can be crushed only by actually breaking the cells. 
As the fruit ripens, this cementing material slowly hydrolizes, prob¬ 
ably by enzymatic action, into substances more readily soluble in water. 
This material is that generally referred to under the name “pectin,” and 
its formation, which occurs slowly under natural conditions, may be greatly 
hastened by boiling with water. Pectin, according to some investigators, 
can be further split by hydrolysis, either with boiling water or by boiling 
with acids or alkalis. With alkalis, pectic acid is first formed, followed 
by meta-pectic acid after prolonged boiling. Meta-pectin, a closely simi¬ 
lar substance, has also been formed. The products of final hydrolysis 
have usually been pentose sugars and galactose. More recently Schryver 
and Haynes (25) and Ehrlich (//) have worked upon the chemical nature 
of pectins. The former reported that the pectin obtained from a number 
of fruits was essentially identical and found the molecule to contain 
pentose sugars sufficient to account for about one-third its weight. 
Ehrlich reports pure pectin as consisting primarily of arabinose, galac¬ 
tose, and galacturonic acid. 
The changes in the pectins as they occur naturally in the fruits have 
not been worked out in association with the physical changes in the fruit. 
"The fact seems well established that the cementing material in green 
fruits is calcium pectate, and that this material accounts for the hardness 
