118 LOAV SHORES OF TIlOl'ICAL REGIONS. 



CHAP. XI. considerable quantity of brandies and roots with the 

 Tiienrui ^^*^^^' ^^ making experiments on the mangrove upon his 

 fe'iove. arrival at Caraccas. Tlie infusion in warm water was of a 



brown colour, and had an astringent taste. It contained 

 extractive matter and tannin. When kept in contact 

 witli atmospheric air under a glass jar for twelve days, 

 the purity of tlie latter was not perceptibly affected. 

 The wood and roots placed under water were exposed to 

 ]\x]H'n. tlie rays of the sun. Bubbles of air were disengaged, 

 uicuu. which at the end of ten days amounted to a volume of 



40 cubic inches. These consisted of azote and carbonic 

 acid, with a trace of oxygen. Lastly, the same sub- 

 stances thoroughly wetted were enclosed with a given 

 volume of atmospheric air in a phial. The whole of the 

 oxygen disappeared. These experiments led him to 

 think that it is the moistened bark and fibre that act 

 upon the atmosphere, and not the brownish water which 

 formed a distinct belt along the coast. Many travellers 

 attribute the smell perceived among mangroves to the 

 disengagement of sulphuretted hydrogen ; but no ap- 

 pearance of this kind was observed in the course of 

 these investigations. 

 ohseiv.it inns " Besides," says Humboldt, " a thick wood covering a 

 of iiumboiat. muddy ground would diffuse noxious exhalations in the 

 atmosphere, were it composed of trees which in them- 

 selves have no deleterious property. Wherever man- 

 groves grow on the margin of the sea, the beach is 

 peopled with multitudes of mollusca and insects. These 

 animals prefer the shade and a faint light ; and find 

 shelter from the waves among the closely interlaced 

 roots which rise like lattice-work above the surface of 

 the water. Shells attach tliemselves to the roots, crus- 

 taceous animals nestle in the hollow trunks, the sea- 

 weeds which the wind and tide drive upon the shore re- 

 main hanging upon the recurved brancdies. In this 

 manner the maritime forests, by accumulating masses of 

 mud among their roots, extend the domain of the con- 

 tinents ; but, in proportion as they gain u])on the sea, 

 ihey scarcely experience any increase in breadth, their 



