170 FUNDAMENTALS OF FRUIT PRODUCTION 



starch molecule in order to gain some idea of the factors involved in its 

 formation. When starch is hydrolyzed slowly, it yields maltose and 

 dextrin. Both of these yield glucose on further hydrolysis. Corn 

 starch contains palmitic acid, a fatty acid and a related unsaturated 

 compound. These fatty substances are liberated only after hydrolysis 

 and are probably attached to the carbohydrate of the starch molecule. ^^^ 

 There is enough fatty acid in the corn starch molecule to make com- 

 mercially profitable, in the manufacture of glucose from corn starch, 

 the use of this residue as soap stock. Moreover, starch probably is not 

 chemically homogeneous. At least two substances with distinct prop- 

 erties have been separated and called amylose and amylopectin. 



When the concentration of hexoses is sufficiently great, starch is 

 usually formed in the plastids. In fact, leaves of plants such as the 

 onion which do not ordinarily form starch, will do so when floated on a 

 10 per cent, solution of fructose. 



Starch will be formed, therefore, whenever the concentration of 

 sugars reaches a certain point and other conditions such as temperature 

 permit. In the summer and early autumn, starch is stored in the 

 branches. In the peach, great amounts are found in the leaf gaps. In the 

 younger apple shoots, it accumulates predominantly in the pith, being 

 especially abundant at the nodes. 



The association of fat with the starch molecule indicates that the 

 latter is the starting point for fat formation in plants. Fatty oils there- 

 fore may be considered as a reserve food derived from carbohydrates 

 especially in fruits like the avocado, in the seed of fruits like the apple 

 and cocoanut and also over the winter in the younger roots and branches. 

 Fats are esters which yield on hydrolysis one molecule of glycerine and 

 three molecules of fatty acids. The commonest fatty acids found in 

 plant fats and oils are: (1) oleic acid, in olive oil, almond oil, quince oil, 

 cherry-, plum-, peach- and apricot-kernel oil; (2) linolic acid, in the oils 

 from pumpkin, watermelon, melon, apple, pear and orange seeds; (3) 

 palmitic acid, in cocoanut oil and cocoa butter and (4) dihydroxystearic 

 acid, in grape-seed oil. Fats contain less oxygen in proportion to the 

 carbon present in the molecule than carbohydrates. They, therefore, 

 yield more energy when oxidized and may be regarded as concentrated 

 energy in chemical combination. 



Sucrose and even glucose must at times be considered forms of carbo- 

 hydrate storage. 



Seasonal Fluctuations of Stored Carbohydrates. — The seasonal varia- 

 tion in the carbohydrate content of plants gives evidence of storage. 



Easily Hydrolyzable Carbohydrates. — ^Leclerc du Sablon's^'^ deter- 

 minations of the easily hydrolyzable carbohydrate in the roots and 

 branches of the pear and chestnut are given in Table 59. This type of 

 carbohydrate which includes sugars, starch and other easily hydrolyzed 



