STRUCTURE AND GROWTH 15 



cambium which heals wounds and covers over 

 cavities. 



More specifically, the cambium is a layer of cells 

 lying between the wood and the bark of the tree, 

 which, under proper conditions of temperature and 

 nutriment, have the power of growth and division; 

 that is, of producing new cells. Most of the new 

 cells produced by this multiplication are deposited 

 either on the wood which is inside the cambium, 

 or on the inside surface of the bark, which is out- 

 side the cambium, and these cells quickly lose the 

 characteristics of cambium cells and become special- 

 ized wood or bark cells. They of course no longer 

 have the power of growth or division, and in that 

 sense all the cells in the trunk except the cambium 

 cells and the innermost bark cells, which in many 

 ways work with the cambium, are dead. 



Leaving the cambium for a time, let us glance 

 at the other regions of the trunk. The sapwood 

 has for its function the conveyance of water (with 

 small amounts of minerals dissolved therein) from 

 the roots to the leaves. The sapwood (of the 

 roots as well as of the trunk and branches) also 

 acts as a storehouse in which digested food is laid 

 up over winter. The principal effect of the re- 

 moval of sapwood from the tree is that the water 

 supply of the leaves is cut off. 



The heartwood has no physiological function, 

 though it may help the sapwood a little at lifting 



