LOW SHORES OF TROPICAL REGIONS. 135 
thesun. Bubbles of air were disengaged, 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 substances 
thoroughly wetted were enclosed with a given vo- 
lume 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 hy- 
drogen, but no appearance of this kind was observed 
in the course of these investigations. 
“ Besides,” says Humboldt, “a thick wood cover- 
ing a muddy ground would diffuse noxious exhala- 
tions in the atmosphere, were it composed of trees 
which in themselves have no deleterious property. 
Wherever mangroves grow on the margin of the 
sea, the beach is peopled with multitudes of mol- 
lusca 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 themselves to the roots, crustaceous animals 
nestle in the hollow trunks, the seaweeds which 
the wind and tide drive upon the shore remain 
hanging upon the recurved branches. In this man- 
ner the maritime forests, by accumulating masses 
of mud among their roots, extend the domain of the 
continents ; but, in proportion as they gain upon 
the sea, they scarcely experience any increase in 
breadth, their very progress becoming the cause of 
their destruction. The mangroves and the other 
