146 BOTANY FOR YOUNG PEOPLE. 



perceive now why they are termed endogenous, 

 as they grow from the centre outwards. When 

 a European wood cutter, it has been well re- 

 marked, begins to fell a tree of this description, 

 he is quite astonished at his hardness. l If I 

 have so much difficulty with the outside,' says 

 he. ' how shall I ever get through the heart of 

 the wood ?' But as he proceeds, he rinds that 

 the trees of the tropical climates have tender 

 hearts though hard surfaces. It is said that 

 this renders them peculiarly appropriate for 

 making masts of vessels and pipes to convey 

 water. 



Exogenous trees toper from the bottom to the 

 top, and send off branches on all sides, which 

 the endogenous rarely do ; they more or less, in 

 all cases, resemble a cone in shape. The stem 

 is composed of the wood and bark. In the cen- 

 tre is the pith which answers somewhat like the 

 marrow that is in our bones for the purpose of 

 nourishing them. This pith or cellular sub- 

 stance is in both endogenous and exogenous 

 stems ; in the former it forms with the woody 

 matter irregular bundles, but has in the latter 

 a radiated appearance, distinguishing the differ- 

 ent kinds at first sight. 



