THE ISTHMUS OF PANAMA. 231 
sidered as constituting an important link between Pandanee and Palms. 
No less surprising is the occurrence of the genera Macleania, Splyro- 
spermum, and Cypripedium in the low coast region, in a temperature 
far exceeding that in which any of their species have hitherto been 
known to exist. 
The aspect of the flora is much more diversified than the uniformity 
of the climate and surface of the country would lead us to expect. 
The sea-coast and those parts influenced by the tides and the im- 
mediate evaporation of the ocean, produce a quite peculiar vegetation, 
among which the Mangroves, chiefly composed of different Rhizophoras 
and Avicennias, are the most remarkable features. Growing in all 
muddy places, down to the very verge of the ocean, they form im- 
penetrable thickets, the abode of alligators, sand-flies, and mosqui- 
toes, and the places, from whose exhalation of putrid miasmata, sickness 
spreads over the adjacent districts. To destroy these dreaded swamps 
is almost impossible: the Avicennias, with their asparagus-like rhizo- 
mata, send up innumerable young shoots whenever the main stem is 
disturbed; the Rkizophoras extend in all directions their long aerial 
roots, which soon reach the ground, and preserve the tree from falling, 
after its terrestrial roots have lifted it high above its original level. - 
At Panama, where the tide rises to the height of twenty-two feet, 
these trees are frequently under water, apparently without being 
in the least injured or checked in their growth. Rivers, as far as 
subjected to the influence of the ebb and flow, are full of Mangroves ; 
and the highest Rhizophoras, which, growing always on that side where 
there is the deepest water, assist the natives in conducting their canoes 
through the mud and sand-banks. Among many other littoral plants 
will be recognized the Prosopsis horrida, Kunth, Orescentia obovata, 
Bth., Cereus Pitajaya, De Cand., Hippomane Mancinella, Linn., Aero- 
stichum aureum, Linn., Ipomæa pes-capre, Swartz, Hibiscus arboreus, 
Desv., Cocos nucifera, Linn., Pithecolobium macrostachyum, Bth., Gui- — 
landina Bonduc, Ait., and several species of Jacguinia, Plumieria, and 
Ruyschia. * 
Far different is the vegetation of the savanas. The ground, being 
level or slightly undulated, is clothed during the greater part of the 
year with a turf of brilliant green ; groupes of trees rise here and there ; 
silvery streams, herds of cattle, and the isolated huts of the natives 
enliven. a scene, over which the absence of Palms and Tree-ferns throws 
