58 BOTANY OF THE VOYAGE OF THE SULPHUR. 
Ill.—WESTERN TROPICAL AMERICA, 
FROM MEXICO TO GUAYAQUIL. 
DirrerENT portions of the west coast of intertropical America were so re- 
peatedly visited between the years 1836 and 1839, that we became familiar with 
its general aspect. There is as much variety and individual force in the character 
of scenery as in many other objects; and the tropical American has its own, quite 
distinct from the Asiatic, though probably not to be very satisfactorily expressed. 
Strictly speaking, intertropical America would include a large portion of Peru, 
and of which the expedition also had some experience. But to the south of Cape 
Blanco, in the Bay of Guayaquil, the vegetation is so exceedingly different from 
what is usually regarded as tropical, that at present, our attention is best confined 
to that range of country which extends between the Bay of Guayaquil and San 
Blas, at the entrance of the Gulf of California, or between 2° 30’S., and 21° 32’ 
N.L. This extensive tract is far from possessing an uniform vegetation, for that 
to the north of Panama differs materially from what obtains to the south. Both 
are, however, excessively tropical ; a boundless forest invests the surface nearly 
every where, and there is a certain uniformity in the physical agents. 
The climate is necessarily tropical, but is not every where synchronous in its 
seasons; at Guayaquil the rains are expected with the new year, but as we 
ascend the coast to the northward they are gradually later, till at San Blas, on the 
limits of the tropics, their accession takes place about St. John’s day in June. 
The influence exerted by them over the vegetation is therefore at various times, 
and between the limits of this tract there will be a difference of nearly six 
months. The relations of the seasons are those usual within the tropics, with the 
exception, that in the Bay of Choco, the period of rains is prolonged even to ten or 
eleven months, and the vegetation is characterised by excessive and rank luxuri- 
ance. In the distribution of temperature, we are not prepared to meet, in these 
latitudes, with any very remarkable diurnal or annual variation, and none such is 
observable within the limits stated above. 
