FOREST FORMATIONS OF THF ISTHMUS OF PANAMA 81 



these are seen mostly in species growing on flat, soft ground, their object 

 being probably to give the tree a broader base and firmer standing. 



On many other characteristic features of the trees and shrubs of the 

 rain-forest fragmentary information has been collected which may be 

 used as a basis for further study ; but while all are very instructive, these 

 data are not sufficiently well defined and grounded to be presented at 

 this time. 



The arrangement of the trees of the rain-forest in successive tiers 

 is a fact which easily strikes the student and has been commented upon 

 by many authors. In the rain-forest of Darien, very tall trees, the 

 crown of which spreads in full sunlight, are not numerous, and it is 

 difficult to procure the necessary specimens for their identification. 

 Besides one or two species of giant fig-trees, I have been able to recog- 

 nize two of the principals and to describe them as new species: Cou- 

 roupita darienensis, the Darien cannon-ball tree, and Coumarouna pana- 

 mensis, a papilionate tree nearly related to the one producing the tonka 

 bean. Of those forming the lower levels we have already a long list. 

 The giant trees just named appear as islands above the general upper 

 surface of the forests, so that the second story from above is really the 

 principal one. As constituents of this level we note, among others, 

 species of Copaifera, Virola, large-leaved Lecythis, Brosimum, Pou- 

 rouma, and at least one tall palm; in the third or middle level there 

 are species of Alseis, Warscewiczia, Guatteria, Eschweileria, Brownea, 

 and an increasing number of palms ; below this we enter into the 

 dominion of shrubs, extremely rich in species, with predominance of 

 Rubiaceae, Piperaceae, and Melastomatace?e. and again a few dwarf 

 palms. The density of the underbrush and immediate covering of the 

 soil is dependent upon the nature of the latter and the amount of light 

 it receives ; grasses and sedges are scarce ; terrestrial Aroids appear in 

 wet places ; thickets of Heliconias and their allies on the richer river 

 flats, while districts with a clayey soil covered with a thin layer of 

 humus will be rendered almost inaccessible by continuous fields of 

 Bromelia karatas. intermixed here and there with patches of the large 

 toothed Ananas. 



Add to this picture numerous vines, sometimes hanging in festoons 

 from the lofty heights, sometimes stretching vertically like as many taut 

 cables, and the luxurious vegetation of epiphytes, covering trunks, 

 branchlets. and even leaves, and a general though imperfect idea of the 

 rain-forests of Panama w ill have been evolved. 



Tn the same way one going from the base to tlie summit of a nionn- 



