THE FUNCTIONS OF THE WOOD 199 



DISTRIBUTION OF CARBOHYDRATE RESERVES 

 IN THE WOOD. 



Starch was present in large quantities in the wood at the 

 time these determinations were made. The cells of the 

 medullary rays, the last few layers of elements formed in 

 each year-ring and the first layer of the next, and the 

 elements in contact with the vessels, were densely crowded 

 with starch grains. The sheath of starch-containing 

 elements round the vessels was continuous, and often 

 many -layered, in the root and in the stem at the ground- 

 level. Higher up only some of the elements in contact 

 with the vessels contained starch, but those which did so 

 were densely packed. Also it was noticed that in this 

 region the first layer of the spring wood was without starch, 

 except where it was in contact with vessels. Generally 

 there appeared fewer starch-containing elements at the 

 higher levels. In the root the number of starch-containing 

 cells is still further augmented by the fact that the vessels 

 are much more numerous, hence the number of elements 

 constituting the starch-bearing sheaths is more considerable. 

 A quantitative estimation of the cross-section of the various 

 elements of the wood in some trees will be given farther on. 

 Leclerc du Sablon (1902) has quantitatively analyzed 

 the wood of the stem and roots of trees at various periods 

 of the year. He examined both deciduous trees and ever- 

 greens. As typical of the behaviour of the former, his 

 results with the chestnut are quoted in the following table. 

 The variations in the carbohydrate content are very great. 

 From these figures it may be seen that the quantities 

 of stable reserves, polysaccharides, far exceed those of the 

 sugars. During the winter there is a diminution in storage 

 products, due mainly to respiration. The sugars increase 

 in the spring, and the polysaccharides (starch, dextrin, 



