164 THE STORY OF THE PLANTS. 



first is, to raise the foliage, with the flowers and 

 fruits as well, visibly above the surface of the 

 ground on which they grow, so that the leaves 

 may gain the freest possible access to rays of sun- 

 light and to carbonic acid, while the flowers and 

 fruit may receive the attentions of insects and 

 birds, or other fertilising and distributing agents. 

 The second is, to conduct from the root to the fo- 

 liage and other growing parts what is commonly 

 called the raw sap that is to say, the body of 

 water absorbed by the rootlets, together with the 

 nitrogenous matter and food-salts dissolved in it, 

 all of which are needed for the ultimate manu- 

 facture of protoplasm and chlorophyll. The third 

 is, to carry away and distribute the various ma- 

 tured products of plant life, such as starches, 

 sugars, oils, and protoplasm, from the places in 

 which they are produced (such as the leaves) to 

 the places where they are needed for building up 

 the various parts of the compound organism (such 

 as the flowers and fruit or the growing shoots), as 

 well as to the places where such materials are to 

 be stored up for safety or for future use (as, for 

 example, the tubers and roots, or the buds, bulbs, 

 and other dormant organs). Each of these three 

 essential functions we must now proceed to con- 

 sider separately. 



In order to raise the leaves and branches visi- 

 bly above the ground into the air above it, the 

 stem is made much stronger and stouter than the 

 ordinary leaf-tissue. If the plant does not rise 

 very high above the ground, indeed, as in the 

 case of small herbs, and especially of annuals, its 

 stem need not be very hard or stiff, and is often 

 in point of fact quite green and succulent. But 



