VOL. IIlI.] Forms of Trees. ae 
‘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 ata 
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. 
