8 Forms of Trees. [zoe 



In the tropics the intense heat develops another tree form, the um- 

 brella form. In this region the heat is always accompanied by moist- 

 ure, and is thus never excessive or dangerous for trees which naturally 

 seek the light. The moisture and heat combined produce a most 

 vigorous and dense vegetation, the very opposite to what is found 

 in the arid zones. The effort ot the tree is therefore concentrated 

 in its endeavor to reach the light and to push out from the dense 

 shade nearer the ground. The most vigorous growing trees in this 

 region send up straight and undivided trunks to a level with the top 

 of the dense undergrowth, branch at this level and form immense 

 umbrella-like crowns above less vigorous trees. This umbrella- 

 form gives to the tropical landscape a distinct and characteristic ap- 

 pearance. A tendency to assume such an umbrella-form can also 

 be recognized among those trees of the temperate zone, which grow 

 in moist places, such as river bottoms, canons and other sheltered 

 localities — trees in fact, which delight in moisture. But nowhere 

 is the form so pronounced as in the tropics, where it is common 

 with all large species of the denser forests. The uplands of the 

 tropics, where the rainfall is less and where heat and drying winds 

 are more powerful, and where accordingly the vegetation is less 

 dense, the umbrella form is rare, or where it exists is caused by other 

 agencies. 



The origin of the tropical umbrella form is therefore not exactly 

 identical with that of the umbrella form assumed by most pines in 

 such districts as the Mediterranean or the gulf region of the United 

 States, and to a certain extent also by a few more northern pines. 

 This umbrella form is caused by the fallingoff of the lower branches, 

 which never possess the strength of the upper limbs. The um- 

 brella form, however, greatly favors their struggle against wind and 

 heat. 



In these drier places in the tropical districts the umbrella form 

 gives place to the globular form, the conditions there being quite 

 similar to what they are in the drier regions further north. Ob- 

 serve, for instance, the form of the ceiba ( Bombax Ceiba), which 

 inhabits dryer localities in the Central American tropics. This tree 

 is almost globular in shape, in order that its branches may give 

 necessary shelter to the trunk, and to keep away the reflected heat. 

 An effort to change the form of this tree by pruning results fatally, 

 as the branches become sun scalded and a prey to borers which 



