122 PHYSICAL GEOGRAPHY.

 

’ and in their turn send out other branches, and in this
way an extended area is covered. A single tree has been
known sufficiently large to give shade to 7000 men at the
same time.

The Llanos of the Orinoco are found in the
tropical zone. During the dry season, they are
almost entirely devoid of vegetation ; but during
the wet season, they are covered with grasses.

The Indian Archipelago affords an excellent illustration
of the wonderful luxuriance of the vegetation of the
tropics. Here the gigantic Rafflesia bears flowers three
feet in diameter!

In the northern and southern portions of the
tropical zone, where the mean annual temperature
ranges from 79° to 73° Fahr., the vegetation,
though similar to that of the equatorial regions,
begins to lose its density and luxuriance. The
forests contain less undergrowth and fewer para-
sitic plants. Tree-like ferns and figs are espe-
cially abundant, and some authorities have ar-
ranged these portions into separate zones, called
the zones of tree-ferns and figs.

319. The Sub-Tropical Zones, or the Zones of
Laurels and Myrtles, extend in each hemisphere,
from the isotherm of 73° Fahr. to 68° Fahr.
Here, the heat of summer, though sufficient to
ripen most of the tropical fruits, is not as intense
as in the tropical zone. The winters are mild,
and scarcely arrest the vegetation. The palms and
bananas of the preceding zones are still common,
but the characteristic vegetation is found in the
abundance of trees with thick, shining leaves, such
as the laurels, magnolias, and myrtles.

320. The Warm Temperate Zones, or the
Zones of Evergreen Trees, or trees which do not
shed their leaves, extend in each hemisphere,
from the isotherm of 68° Fahr. to 55° Fahr. In
this zone, trees with thick, shining leaves occur,
mingled with oaks, beeches, and others similar to
those found in our own forests. No palms occur,
but in their place we find a number of glossy-
leaved evergreen trees, and handsome evergreen
shrubs.

In those portions of this zone which are in the neigh-
borhood of the Mediterranean, the bay, myrtle, laurel, fig,
and the olive, are characteristic. The cork oaks, chest-
nuts, and pomegranates, are frequent. The vine, said to
be a native of this zone, attains here its greatest growth,
the stem often reaching a thickness of half a foot. In
America, oaks, pines, and tulip-trees occur.

The southern warm temperate zone includes
portions of New Zealand and Australia, and in
South America the Pampas of the Rio de la
Platte, where tree-like grasses abound.

 

 

321. The Cold Temperate Zone, or the Zone of
Deciduous Trees, or those which drop their leaves
in autumn, extends in the northern hemisphere,
from the isotherm of 55° Fahr. to 41° Fahr. For-
ests of deciduous trees are the main characteristics
of this zone ; oaks, birches, beeches, chestnuts, wal-
nuts, maples, elms, larches, alders, and sycamores,
are among the most common of the deciduous
trees. Mosses and lichens frequently cover the
trunks of the trees, and a rich and varied under-
growth occurs; the holly, clematis, wild rose, hon-
eysuckle, and rhododendron, are examples.

Extensive meadows, covered with grasses, are
found in this zone.

The deciduous character of the trees, and the almost
total absence of evergreens, produce a marked contrast
between winter and summer. During winter, the foliage
almost entirely disappears, and snow covers the ground
for long periods.

This zone is essentially one of extensive forests.
In connection with, the warm temperate zone of
the northern hemisphere, it has always contained
the most highly civilized races of men, and is es-
pecially rich in the number and luxuriance of its
food-plants.

322. The Sub-Arctic Zone, or the Zone of the
Cone-Bearing Trees, extends in the northern hemi-
sphere, from the isotherm of 41° Fahr. to regions
where the mean annual temperature for the month

 

Fig, 106, Pine-Trees.

of September is 36.5° Fahr. In this zone, both
forests and grassy meadows abound. The forests
are especially characterized by cone-bearing trees,
with evergreen, shining, needle-shaped leaves, such