PLANT STEMS 191 



arrangement of the layers in one and the absence of all such arrange- 

 ment in the other. 



In Experiment 97, when the cross section of a dicoty- 

 ledonous tree was examined, it was found to be composed 

 of circular rings, but no such rings are found in the cross 

 section of the monocotyledonous tree. When later we 



A BANYAN TREE. 



Some of its branches descend, and take root in the ground, and so appear 

 like stems. 



examine the seeds of corn and bean, we shall find that 

 they also differ very much. 



When the bark is removed from a stem, like the willow 

 or apple, the soft smooth layer underneath is found to be 

 composed of living cells. This is called the cambium 

 layer. During the season of growth, 'these cells are con- 

 tinually subdividing and forming new cells, thus adding 

 to the thickness of the stem. The age of a tree can be 



