322 THE REASON WHY. 



" And when he sa\v a fis? tree in the way, he came to it, and found nothing thereon, 



but leaves only, and said unto it, Let no fruit grow on thee henceforward for 



ever. And presently the tree withered away." MATTHEW xxt. 



1274. Why have trees with large trunks a great number 

 of leafy brandies ? 



Because it is by the leaves that the secretion is formed which 

 supplies the woody fibre. The number of leaves on a tree, therefore, 

 generally bears a relation to the size of its trunk, and the number 

 of its branches. 



1275. Why have poplar-trees comparatively few branches 

 and leaves ? 



Because their trunks are comparatively small, although they 

 grow to a great height. 



1276. Why had the mammoth-tree comparatively few leaves 

 in relation to the immense size of its bark? 



Because the woody texture of this tree (Wellingtonea 

 gigantea) is exceedingly light and porous. It is, in fact, lighter 

 than cork, and, therefore, requires less leaf-produce in its formation. 



1277. Why have oak-trees an abundance of leaves? 

 Because their wood is so dense that they require a larger amount 



of the wood-forming secretion which is supplied by the leaves. 



1278. Why are the trunks of trees round? 



Because, generally speaking, the leaves are distributed upon 

 branches around the trees in every direction. They consequently 

 send down the wood-forming principle on all sides. When a trunk 

 is unduly developed on one side, it may generally be traced to the 

 unequal distribution of the branches. 



1279. What are exogenous stems ? 



Exogenous stems are those that grow by the addition of wood 

 on their outer surface, underneath the bark. 



1280. What are endogenous stems ? 



Endogenous stems are those that grow inwardly, from the 

 centre. Trees of this class, of which palms are the bc>st 

 example, are almost peculiar to tropical climates. 



1281. Why do endogenous stems chiefly abound in tropical 

 climates ? 



Because, probably, the excessive heat of those climates wouW 



