VOL. I. | Forms of Trees. 9 
eventually destroy the tree. In crossing Central America I was 
especially impressed by these different tree forms, characteristic of 
different regions. Along the lowlands of the Pacific Coast up to 
2,000 to 3,000 feet, the characteristic form of the various strong. 
growing trees was the umbrella form. Above 3,000, and from that 
altitude towards the interior in the dry and warm district the globu- 
lar form predominates. As we ascend the interior highlands in the 
vicinity of Coban the climate suddenly changes and becomes very 
moist. With this change comes also a change in the form of the 
trees which here assume the regular umbrella form. The same 
climate continues uninterrupted to the Atlantic Coast, and the 
district is characterized throughout by the predominating umbrella 
form. 
All trees require more protection when young, and this explains 
why young trees are shaped differently from older trees. Thus the 
form of a young specimen of the common blue gum (Aucalyptus) 
is well known. While young the tree is pyramidal and the slop- 
ing branches are covered by horizontally extended leaves. No 
form can be more adapted to withstand heavy winds. As the tree 
grows older, the stem stronger, and the roots penetrate deeper, this 
original form is not required any more, and the tree assumes a 
semi umbrella-like crown. 
If we consider the principal forms of trees in their connection 
with influences of wind, snow, rain, sunshine and heat, we find that 
the various forms may be grouped principally under the following 
heads: 
A. The upright form, with a central undivided trunk and with 
downward sloping branches. This form is possessed by most conifers 
inhabiting snow-visited regions. The downward slope of the 
branches facilitates the shedding of the snow, while the undivided 
trunk offers less resistance to heavy loads of snow. Forked or 
branched trunks would split or break. 
This form may be either necessary to the species, as when the 
latter is confined to snow-visited districts (example Picea amabilis ), 
or it may be inherited and continue as a characteristic of the species 
which grows in a warmer climate, but which evidently had been 
evolved from a species which once inhabited colder regions. Ex- 
ample: the redwood (Seguova sempervirens), Lawson cypress ( Cu- 
pressus Lawsoniana), and many other evergreen trees inhabiting 
