WHERE THE TREE IS ALIVE 



This section of the trunk of a small 

 tree is pictured in such a way as to 

 expose the cambium layer, just beneath 

 the outer bark. In this layer are located 

 all the protoplasmic cells, aside from 

 those in the leaves and roots, that are 

 really alive. A portion of the woody 

 tissue just beneath the cambium 

 conveys the watery solution upward 

 from the roots; but the return flow of 

 sugary sap takes place solely in the 

 cambium layer, where also the proto- 

 plasmic or life activities go on, through 

 which the tree grows; growth itself 

 being due to the deposit of material 

 produced in the leaf cells. The central 

 wood fibers of the trunk are totally 

 dead. 



