VOL. III.] Partus of Trees. 9 



e\'entually 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 3'oung trees are shaped differently from older trees. Thus the 

 form of a young specimen of the common blue gum ( Eticalypttts) 

 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 w-hich evidently had been 

 evolved from a species which once inhabited colder regions. Ex- 

 ample: the redwood (Sequoia sempervirens), Lawson cypress ( Cu- 

 pressus Lawsoniana), and many other evergreen trees inhabiting 



