250 TIMBER AND SOME OF ITS DISEASES. [CHAP. 



a portion but a very large portion of this starch 

 and sugar : we can trace them down the vascular 

 bundles of the venation, through the leaf-stalk, into 

 the cortex, and eventually to the cambium-cells ; and 

 it is necessary to be quite clear on the following 

 points : (i) the cambium-cells, like all other living cells 

 which contain no chlorophyll, need to be supplied 

 with such foods as sugar, starch, &c., or they starve 

 and perish ; (2) since these foods are prepared, as we 

 have seen, in the leaves, and in the leaves only, it is 

 obvious that the vigour and well-being of the cam- 

 bium depend on the functional activity of the leaves. 



We have already seen how the cambium-cells gi 

 rise to the young wood, and thus it will be clear how 

 the formation of timber is dependent on the functional 

 activity of the leaves. Moreover, it ought to be 

 mentioned, by the way at least, that it is not only the 

 cambium which depends upon the leaves for its 

 supplies all the roots, young buds, flowers, and fruits, 

 &c., as well as the cortex and cork-forming tissues, are 

 competitors for the food supply. Now it is clear that 

 if we starve the buds there will be fewer leaves 

 developed in the following year, and so next year's 

 cambium will again suffer, and so on. 



I have by no means traced all the details of even 

 the first ramifications of the complex network of 



2S. 

 )W 



