650 



NATURALIST'S GUIDE TO THE AMERICAS 



vember; and the short wet, December 

 and January. There is considerable 

 variation in these seasons, and occa- 

 sionally a short season is almost 

 eclipsed. The rains offer no impediment 

 to research. There is no real period 

 of drought and only three-fifths of the 

 rain falls during the two rainy seasons. 

 The ranfall along the coast increases 

 from east to west from 84 to 100 in., 

 and towards the interior to 150 in. 

 along the eastern foothills of the Paka- 

 raima mountains. In the savanna re- 

 gion it is much lower, amounting to 

 about 60 in. 



ORIGINAL BIOTA 



1. The vegetation 

 A. General 



Knowledge of the flora and vegetation 

 of British Guiana is still far from com- 

 plete, and only the merest outline of 

 the leading features of the colony can 

 be given. 



The coastal swamps are occupied by 

 the usual mangrove thickets, in which 

 the black mangrove (Rhizophora) , the 

 white mangrove {Laguncularia) , and 

 the courida (Avicennia) are abundant. 

 These swamps extend up the principal 

 streams to the limit of the influence 

 of salt water. 



Fresh-water swamps and marshes 

 parallel the rivers throughout the 

 coastal lowlands, and are generally 

 subject to inundation during the rainy 

 seasons and at every high tide. At 

 the water's edge the tall mucca-mucca 

 (Monirichardia) is abundant, and farther 

 back the wild cacao {Pachira), the 

 pumpwood (Cecropia), and the trysil 

 (Pentaclethra) are characteristic, to- 

 gether with several species of palms 

 of the genera Mauritia, Euterpe, and 

 Manicaria. The whole is bound to- 

 gether by masses of vines, particularly 

 of the dogbane and milkweed families. 



Aside from a narrow strip of cultivated 

 land along the coast and the lower 

 courses of some of the rivers, the re- 

 mainder of the coastal lowlands and the 

 sand and clay belt is covered with rain- 



forest. It is at present impracticable 

 to distinguish or describe the various 

 plant associations, further than to 

 state that two general types of forest 

 may be distinguished, the one on the 

 clay hills, and the other on the sand 

 ridges (luxuriant tropical rain-forest). 

 The forest-cover is 124 to 150 ft. high; 

 the trees are straight and unbranched 

 for 60 to 75 ft. A second layer of 

 smaller trees is usually well developed. 

 Lianas are abundant and of large size, 

 while practically every tree is occupied 

 by epiphytic ferns, orchids, and bro- 

 meliads. The undergrowth of shrubs 

 and the ground cover of herbaceous 

 plants depends in general on the avail- 

 able light, and is best developed along 

 the stream banks. The great majority 

 of species are woody. 



The flora of these forests is extremely 

 rich and much of it is still unknown. 

 Among the hundreds of species of trees, 

 many of the commoner or more im- 

 portant are included in the genera 

 Eperua, Dimorphandra, Inga, Ma- 

 chaerium, Caraipa, Lecythis, Nectandra, 

 Licania, Hevea, and Mimusops. The 

 smaller trees and shrubs are largely 

 members of the myrtle, melastome, and 

 madder families. The herbaceous flora 

 includes numerous species of the arrow- 

 root, gesnera, and sedge families, to- 

 gether with numerous ferns and 

 lycopods. 



Higher ridges of pure sand are fre- 

 quently occupied by an open forest of 

 low trees with wide-spreading crowns, 

 in which Dimorphandra is characteristic, 

 and under which there is a luxuriant de- 

 velopment of shrubs, herbs, and grasses 

 showing in specific composition rela- 

 tions to the savanna vegetation of the 

 hinterland. 



Extensive savannas occupy most of 

 the southern half of the colony, covering 

 the high plateaus and broken onlj' by 

 belts of forest along the streams and on 

 some of the mountain slopes. The 

 vegetation here is composed chiefly 

 of several species of tall grasses and 

 sedges, with numerous herbs and low 

 shrubs as secondary elements, and 



