VOL. III.] Forms of Trees. ir 



undivided stems and sloping branches indicate their origin in the 

 snowy regions in the north. 



C. The globular form. This form is possessed by trees in warm 

 and dry regions or localities. The object of the form is to protect 

 the tree from sun and heat, and to preserve the moisture in the soil 

 around the root. Example: the live-oak, the wild California wal- 

 nut, the Texas umbrella, and the tropical ceiba, or Bombax tree. 

 The mesquite of the Mojave desert belongs to this form. 



D. The umbrella form. This form is principally found in moist 

 tropical climates. The object of the form is to give to the tree as 

 much sun and heat as possible, which can again only be had at a 

 certain altitude above the tops of the dwarfer vegetation. Example: 

 various papilionaceous trees, as well as most varieties of trees in the 

 tropical lowlands of both continents. 



In connection with this, I will call attention to the form of the 

 bases of the trunks and of the surface roots in trees growing in 

 moist places, especially in the tropics. The trunks branch out above 

 the soil and form peculiar horizontally compressed roots, sometimes 

 five to six feet high, but only a few inches thick. Such surface 

 roots are found in most tropical trees, as well as in many swamp 

 trees; for instance, the swamp cedar of the Mississippi delta. The 

 object is to steady the tree when floods or excessive rains soften 

 the ground; round roots would then offer much less resistance. 



I have here merely tried to outline the principal forms of trees 

 and their trunks and branches, and have endeavored to state the 

 causes which have been at work in moulding them. 



There are, however, many other agencies which assist in forming 

 the shape of trees. Such are the elasticity of the wood, which would 

 make the pyramidal shape of the tree less necessary; hairiness of 

 the leaves, which tends to counteract sun and dryness; a tough and 

 thick bark, which would also render sun and heat less injurious — all 

 these must be taken in consideration when we study the forms of 

 trees. 



