6 STRUCTURE OP THE STEMS OF TREES. 



scious of, and which is totally unpossessed by small 

 ones. 



In England, the trees are all of the class called 

 " exogenous/' that is to say, they have numerous 

 and spreading branches; the leaves, when held 

 between the eye and the light, are found, if broad 

 enough, to be marked in every portion by net-work 

 of green lines, technically called the "veins;" 

 and upon the outside of the trunk there is bark, 

 which can be removed like the peel of an orange. 

 When one of these exogenous or branching trees 

 is cut down, or if a branch be lopped off, the exposed 

 end, on being polished, shows concentric circles 

 surrounding a central point, which in young parts 

 of the tree indicates a column of living pith. The 

 concentric circles announce the age of the tree or 

 branch, which usually is just as many years old in 

 that part as there are rings. In its earliest stage, 

 or while in its first season of growth, the stem of 



SECTION OF EXOGENOUS STEM. 



the seedling tree consists only of pith and an en- 



