FORMATION OF WOOD AND BARK. 79 



their father, " are indeed true signs of the PINE 

 tribe, the members of which all bear cones, and 

 are therefore called Conifers : and also have pe- 

 culiar spiny leaves, and contain an abundance of 

 strong-smelling resin. But can you tell me whether 

 they are endogens or exogens ?" 



Mary said she could hardly tell by looking at 

 the leaves, because they were so narrow, but she 

 fancied they were straight-veined. Henry did not 

 think so, and he felt sure the trees were exogens, 

 from their hard and woody growth. Robert, too, 

 remembered that his father had said that all our 

 forest trees are exogens, so this settled the matter 

 yet they were told that because of some differ- 

 ences connected with the seed, these trees have 

 sometimes been considered a distinct class. 



"I shall scarcely do wrong, however," said 

 their father, " in calling them the lowest race of 

 exogens, from which they do not differ in growth, 

 but increase exactly in the same manner, by 

 yearly additions to the outer portion of the wood." 



" I cannot understand how trees get their new 

 layer every year without our noticing it," said 

 Mary ; " there are the elms at the end of the gar- 

 den, with their rough old trunks ; I play under 



