12 
LauracecB, Myristicece, Scitaminece, Musacece, and Pipe- 
racecB, which prevail in equatorial forests, and perfectly 
characterise tropical vegetation ; but they do not do so 
more than the Anonacece, Dilleniacece, Guttiferce, Auran- 
tiacecB, Dipterocarpece, Sapindacece, Meliacece, Combre- 
tacece, Cinchonacece, Bignoniacece, Ebenacece, Sapotea:, 
CycadacecB, Bromeliacece, Pandanacece, and many others. 
As tropical climate is not terminated by an abrupt line, but, 
according to the influence of local causes, extended into 
higher latitudes, so does it carry with it the peculiarities 
of tropical vegetation. Thus, if the country be open 
towards the equator, the equinoctial rains will be blown 
with the periodical winds to much higher latitudes than 
where a mountain range intervenes, or the course of the 
winds is diverted by a high and shelving coast. Hence 
India, open to the south, is deluged by the periodical 
rains ; while Egypt, in the same latitude, owes its fertility 
only to the overflowing of the Nile. The same effects may 
ensue, if the same causes operate, along a valley or a 
mountain range. Thus, Humboldt has shewn that, in the 
basin of the Ohio, Gleditsia monosperma, the Catalpa, 
and Aristolochia Sipho, extend three degrees further north 
than on the coast of the Atlantic. So, along the base of 
the Himalayas, where there is considerable moisture of the 
soil, a vigorous vegetation has sprung up, which adds to 
the humidity of the atmosphere, as well by exhalation 
from its leaves as by preventing free evaporation from 
the ground. A greater equality of temperature is also 
preserved, from the umbrageous covering at once im- 
peding the ready absorption of heat by day, as it checks 
free radiation during the night. Hence, along this tropic- 
girt base, with greater equability of temperature, we find more 
uniform moisture than in the open plains; and in it many 
plants extending several degrees further north than they 
do in any other part of India; as, a species of Cinna- 
