MANUFACTURE AND UTILIZATION OF CARBOHYDRATES 175 



by respiration, translocation to the leaves and fruit, and utilization in the 

 formation of complex carbohydrates. The assimilatory activity of the 

 leaves soon restores the sugar content of the spurs, but a marked increase 

 does not commence until September, This is due to continued demands 

 for sugar by the developing fruit on bearing spurs and to starch accimiula- 

 tion in non-bearing spurs. The increase in sugars after September is 

 associated with the decrease in starch during this period and represents a 

 partial conversion of starch to sugars. Some of this sugar is sucrose, 

 a form in which carbohydrate is stored during the winter, as the figures 

 in Table 6-4 show. 



The sugar used in the development of fruit is considerable, as Table 

 65 indicates. In the apple, the percentage and absolute amounts in 

 the fruit increase steadily, the rate of increase becoming greater as 

 maturity approaches. This holds for prunes also.^^^ In pears the 

 percentage decreases at first and then increases, while the absolute 

 amounts increase steadily. In either case the increase in absolute 

 amount extends to the end of August or the middle of September. 



Michel Durant^^'' points out that a period of carbohydrate synthesis followed 

 by one of hydrolysis and simplification is found in fruits as well as in leaves. 

 Ripe fruit therefore contains more sugar than unripe fruit. The increase in the 

 sugar content may continue even after the fruit is picked. This occurs in drying 

 prunes when sugar is formed by the hydrolysis of starch. If prunes after 

 removal from the tree are exposed to the sunlight for 2 or 3 days, their sugar 

 content increases, but after 5 days' exposure their sugar is rapidly consumed in 

 respiration and fermentation.'*^ 



In recapitulation, it is emphasized that the carbohydrate supply 

 of the plant is manufactured in the leaves and that the leaves supply the 

 entire plant. In consequence, movement of carbohydrate is usually 

 away from the leaves to the growing points, cambium and storage organs. 

 Carbohydrate is stored mostly in the immediate vicinity of places where 

 it may later be used. Thus the work of Magness'^s andof Curtis" indi- 



