182 THE STORY OP THE PLANTS. 



each year they rise higher and higher into the 

 air, and produce a fresh bunch of leaves at their 

 summit, they seldom branch, and they never 

 produce large buttressed stems like the oak or 

 the chestnut. 



The second main function of the stem is to 

 convey the raw sap absorbed by the roots to the 

 leaves and branches, and especially to the 

 growing points. This is such a very important 

 element in plant life that we must now consider 

 it in some little detail. 



If you look for a moment at a great spreading 

 oak-tree, with its top rising forty or fifty feet 

 above the level of the ground, and its roots 

 spreading as far and as deep beneath the earth, 

 you will see at once how serious and difficult a 

 mechanical problem it is for the plant to raise 

 up water from so great a depth to so great a 

 height without the aid of pump or siphon. For 

 the plant can no more work miracles than you 

 or I can. Yet every leaf must be constantly 

 supplied with water, that prime necessary of 

 life, or it will wither and die ; and every growing 

 part must obtain it in abundance, in order to 

 give that plasticity and freedom which are 

 needful for the earlier constructive processes. 

 Protoplasm itself can effect nothing without the 

 assistance of water as a solvent for all materials 

 it employs in its operations. 



How does the plant get over these difficulties ? 

 Well, the stem is well provided with a whole 

 system of upward distributing vessels in which 

 water jnay be conveyed to the various parts, 



