MANUFACTURE AND UTILIZATION OF CARBOHYDRATES 173 



carbohydrate content of bearing spurs in May may be associated with 

 flowering. The higher maximum in these same spurs in September is 

 probably connected with the development of specialized tissues in the 

 purse during fruit development. 



The study of the various types of carbohydrate, particularly starch 

 and sugars, shows similar seasonal fluctuations despite some variation. 



Starch. — The only analytical data on the seasonal variation in starch 

 content are on spurs. In woody tissues, starch is a relatively small 

 fraction of the total polysaccharides, but probably a significant fraction 

 of the available carbohydrates. Figure 18 shows the starch variations 

 in bearing, non-bearing and barren spurs of the apple. ^°° 



z: s: 



c^ 



Fig. 18. — Starch content of apple spurs in percentages of dry weight; bearing spurs 

 represented by continuous lines, non-bearing spurs by broken lines and barren spurs by 

 dot-dash lines. {After Hooker. ^^'') 



There are two maxima for starch and two minima. This was shown 

 microchemically by Mer and d'Arbaumont.'^^ The maximum in Septem- 

 ber and the minimum in May correspond to the maximum and minimum 

 for total carbohydrates. The second minimum in January and the 

 second maximum in March are due to conversion of starch to sugars and 

 a resynthesis of starch in spring just before vegetation commences. The 

 second maximum is not, however, so high as the first — except in bearing 

 spurs — which indicates that a certain amount of carbohydrate has been 

 consumed in respiration or used for the formation of other substances. 

 Determinations of the ether extract permit an estimate of the fat and oil 

 content and show that fats increase during the winter. The previous 

 discussion of the structure of starch indicates that this is the point 



