88 THE OAK. 



going into details concerning the use which the plant 

 makes of this starch, and it must suffice to say that the 

 starch serves as the basis of all the constructive materi- 

 als used by the tree. Thus it is converted into a soluble 

 form, and combined with nitrogen, phosphorus, sulphur, 

 etc. (obtained from the earth-salts), to make new proto- 

 plasmic materials, and it passes down from the leaves to 

 nourish all the living cells that require it, in the embry- 

 onic tissue at the apex of the roots, and that at the apex 

 of the stem and branches, buds, etc., and some of it 

 passes to nourish the cambium cells, the developing flow- 

 ers, acorns, etc. ; in short, wherever new organic ma- 

 terial is needed it is supplied from these stores formed 

 by the green leaves waving in the sunshine. If we 

 reflect that the little embryo in the acorn starts its life 

 with only a minute store of starch and proteids in its 

 cotyledon, and that all the tons of organic material 

 (chiefly wood) found in an old oak-tree have been super- 

 added to this by the action of the leaves the small pro- 

 portion of salts taken up by the roots being quite incon- 

 siderable in comparison we obtain some idea of the 

 enormous gain of matter and energy from the outside 

 universe which goes on each summer. 



