190 



fresh stirred, and moistened by rains, alters and 

 vitiates the atmosphere more than that thick 

 wood of plants, which covers an uncultivated 

 soil ! To these local causes are joined other 

 causes less problematic. The neighbouring 

 borders of the sea are covered with mangroves, 

 avicennias, and other shrubs with astringent 

 bark. All the inhabitants of the tropics are ac- 

 quainted with the noxious exhalations of these 

 plants ; and they dread them so much the more, 

 as their roots and stocks are not [always under 

 water, but alternately wetted and exposed to 

 the heat of the sun #. The mangroves produce 



strated by numerous experiments on the humus and earth of a 

 dark colour (carburetted) . It is perhaps at the time that 

 this absorption of oxygen takes place, and in consequence of 

 it, that, according to the complicated action of affinities, these 

 deleterious gaseous combinations with a double or triple 

 basis are formed. 



* The Creoles comprehend the two genera, rhizophora and 

 avicennia, under the name of mangrove, distinguishing them 

 by the epithets Colorado and prieto. The following is a cata- 

 logue of the social plants, that cover those sandy plains on 

 the seaside, and characterize the vegetation of Cumana and 

 the Gulf of Cariaco. Rhizophora mangle, avicennia nitida, 

 gomphrcna flara, g. brachiata, sesuvium portulacastrum (bi- 

 drioj, talinum cuspidatum (vicho), t. cumanense, portulacca 

 pihsa (sargosojy p. lanuginossa, illecebrum maritimum, atri- 

 plex cristata, heliotropium viride, h. latifolium, verbena 

 cuneata, mollugo vertieillata, euphorbia maritima, convolvu- 

 lus cumanensis. These geographical sketches of vegeta- 

 tion were traced on the spot, by entering in a journal under 



