190 
TROPICAL ZONE 
with mesophytic forest. The trees composing the forests 
are of many species, and are very rarely of social habit ; 
they are mostly evergreen and have either simple or branched 
stems. The simple-stemmed evergreens are characteristic 
of these regions ; they are chiefly Monocotyledons, e.g. Palms, 
Pandanaceae, Musaceae, Bamboos, &c. The trees mostly 
have straight trunks reaching to a height of 50 — 150 feet or 
more and bearing their leaves and branches (if any) at the 
top, where they are exposed to the full sunlight. Buttress- 
roots are very often found at the base of the trunk. The 
leaves are mostly more or less leathery with thick cuticle (to 
this is due the characteristic sharp rattle of the rain-drops in 
a tropical forest, and the brightness of the light reflected 
from the leaves) ; they are often corrugated (e.g. in Palms) 
or turned partly edgewise, or they stand with an upward 
slope, or (as in some Leguminosae) move upwards as the 
light becomes more intense, so that they obtain some 
protection against the radiation. The young leaves in some 
plants are produced at all periods of the year, in others 
periodically (often this periodicity has no direct relation to 
that of the climate) ; they have usually good arrangements 
for their protection in the bud, and are very often red in 
colour. Those trees which have not glossy leaves have 
usually rain-leaves with drip-tips. The flowers and fruits are 
very often borne on the older branches or even on the main 
trunk ; the reason for this is not known. Almost nothing 
is known of the relations of flowers and insects in the 
tropics. Many flowers are adapted to sun- or humming-birds. 
Below the larger trees are the shade-loving trees with 
thinner leaves, whose crowns reach a height of about 30 — 50 
feet, and below these again occur large herbs and under- 
shrubs, whilst on the ground are mosses, Selaginellas, 
saprophytes, &c. Besides these, two forms of vegetation 
especially characterise the wet tropical forest — lianes and 
epiphytes, both of which occur in profusion in every 
available space, so that the forest as a whole forms an 
inextricable tangle of the most varied vegetation. Parasites, 
myrmecophilous plants, and other interesting forms are 
often found. 
Grassy openings, except where produced by cultivation, 
are rare in the wettest regions. 
