Hammocks and Everglades of Florida. 271 



formation has led many botanists to conclude, at first glance, 

 that there must be marked soil differences to account for the 

 difference in the vegetation. Yet, strange as this mav seem, 

 it is apparently not the case. The soil in the region about 

 Miami is a more or less porous limestone rock, nearly solid in 

 places but more often \\ith numerous crevices and pits filled 

 with sand. Sometimes the rock lies bare, but perhaps more often 

 it is covered by a layer of sand several centimeters deep. Here 

 and there occur peculiar \vell-like pits from 15 cm. to two meters 

 in diameter and up to three or four meters in depth, the deeper 

 ones containing water, at least at the bottom. These so-called 

 pot holes are probably the result of the solvent action of water 

 at a time w hen the ground was submerged. They are frequent- 

 ly lined by the most delicate ferns, e. g. species of Hymeno- 

 phyllaceae. Except for a greater amount of humus in the soil 

 due to the decay of the dense vegetation it supports, the soil 

 in the hammocks appears the same as that in the pine woods. 

 How, then, can we account for these marked differences in 

 vegetation? The soil is the same, except for the differences 

 noted, and these are better explained as a result of the presence 

 of the hammock than as the cause. Some hammocks seem not 

 to be increasing in size, but the fact that some are spreading 

 would show that it is not entirely a question of soil dift'erences. 

 The writer's observations led him to suppose that the genesis 

 of a hammock is about as follows: Somewhere in the pine woods 

 a few of the small shrubs or occasional small persimmon {Dios- 

 pyros virginiana) or other broad leaved trees of which a few- 

 kinds are found also in the pine woods, form a somewhat sheltered 

 place within which the air is somewhat moister. Here, owing 

 to the increased shade, the soil does not dry out so much as where 

 the sun is more direct. Other trees, favored by this increased 

 moisture of soil and air, especially the live-oak, are thus en- 

 abled to get a start. Soon more trees and shrubs appear, the 

 conditions becoming more favorable the more numerous and 

 larger they become. The whole space underneath the trees 

 grows up to underbrush. The denser the growth becomes and 

 the laiger the trees, the more humid is the air, while the dense 

 shade protects the soil from drying out. Many of the plants 



