Metabolism; Digestion and Translocation 253 



not only the starch of the " seed tuber/ 7 but also practi- 

 cally all of the starch which is made daily by the leaves, in 

 the production of stem and leaf structures - - additional 

 starch-making surfaces. The growth of new tubers 

 develops slowly at first, but finally the energy of leafy 

 shoot " vegetation ' wanes, and then a considerable sur- 

 plus of carbohydrate is accumulated as starch in the 

 tubers. In consequence, at maturity about 80 per cent 

 of the dry matter of the tuber is starch. 



When a tree ceases to make food-material in the fall, 

 there may be little or there may be much starch already 

 accumulated. A peach tree, for example, heavily laden 

 with young fruit in July may make each day a considerable 

 quantity of starch. The latter may be found by the 

 usual test applied to the leaves. The starch, however, is 

 in considerable part used every day to furnish the carbo- 

 hydrate used in the building of wood, in the making of 

 fruit, and ultimately in respiration, so that only when the 

 fruit is becoming ripe and the development of new wood 

 is checked may there be a surplus of starch to accu- 

 mulate in trunk and branches. After the ripening of the 

 fruit much more starch may be made and accumulated' 

 in the twigs as a reserve for the young growth of another 

 season. Such accumulations of food-material are indis- 

 pensable, for in the peach thousands of blossoms are 

 produced and the fruit set before the leaves are unfolded, 

 a result of using food-materials that represent the work 

 of the previous season. 



Many varieties of apple do not ripen until after the 

 leaves fall, and it is possible that this holding and sustain- 

 ing of the fruit so long (meanwhile using stored food- 



