88 THE OAK 



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

 the starch serves as the basis of all the constructive 

 materials used by the tree. Thus it is converted into 

 a soluble form, and combined with nitrogen, phosphorus, 

 sulphur, &c. (obtained from the earth-salts), to make new 

 protoplasmic materials, and it passes down from the 

 leaves to nourish all the living cells that require it, in 

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

 at the apex of the stem and branches, buds, &c., and some 

 of it passes to nourish the cambium cells, the developing 

 flowers, acorns, &c. 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 

 proportion of salts taken up by the roots being quite 

 inconsiderable in comparison we obtain some idea of 

 the enormous gain of matter and energy from the outside 

 universe which goes on each summer. 



