are confined by his will. As we journey
from the poles to the equator, we pass
successively through these belts of vegetation,
strictly subjected to the influence of the laws
of Heat. Passing rapidly from the icy arctic
region, clothed only by the red snow-plant,—
a simple vegetable-cell,—we enter a region
of silky mosses, grey withered lichens, and
low- stemmed alpine plants with tufts of
foliage and of flowers. Next we plunge into a
forest-region of dusky gnarled pines and tall
needle-leaved firs, whose spreading trunks or
mouldering mosses are swathed in a shroud of
dull, sedge-like ferns. Traversing a variegated
Flora, we reach—across the Drontheim line,
where wheat begins—a region in which
flourish the oak with its picturesque boldness
of branching, the yet more noble chestnut
covered with masses of foliage, the lime,
and the elm. In this region, smiling meadows
alternate with shadowy woods; and
the industry of man has covered the face
of the earth with rich and fruitful cornfields.
Scaling the Alps, we descend into a zone of
trees whose shining leaves the winter does
not nip; around whose trunks climb the
vine-boughs; and where, in summer, the
beautiful rock-rose replaces the sweet-
scented hyacinth of spring. This is the land
where

Through the dark green leaves the gold oranges glow.

More fortunate in our power of return
than those martyrs of our race whose
ambition to unfold the mysteries of the
Niger has hurried them to an early grave,
we stretch across the African Desert,
and enter the zone where the tropic sun
vivifying the earth, moist with the heavy vapour
of the ocean, imparts vigour to a matchless
race of plants. Here, the slender date lifts
its tall head on high, and mighty climbers
twine around huge sycamores. The lichen of
the north that sits so modestly in russet
garb on rock or tree and calls no man's
attention to itself, is exchanged for the parasite
with gorgeous blossoms that entwine
itself with the grasp of a boa-constrictor
round some hapless trunk, until it happens to
a tree in the tropics as it has happened in all
climates to men, that the strong parasite
attains the mastery and kills the stem by
which it rose. Here, too, the leafless
spurge prepares nutritious milk, or poisonous
sap—the one hardly distinguishable
from the other, except by careful analysis.
The baobab displays gigantic masses of
wood that have endured six thousand
years; and the dragon-tree, " embosomed in
infinite silence," recounts with speechless
tongue the experiences of fifty centuries of
time.

We have passed through the six regions of
heat's dominions, in which an ever-increasing
warmth of temperature continually gives birth
to a richer and more luxuriant vegetation.
A more condensed but more laborious view
of the compelling influence of heat might be
obtained in toiling up the colossal mountains
of the tropics; from whose summit man
is enabled to contemplate alike all the
families of plants and the stars of the
firmament. Here, the different climates,
instead of being spread over the earth's
surface, are ranged one above the other; and
heat, watching over the accomplishment of
its eternal ordinances, arbitrarily limits the
succession of the forms of vegetation;
imprisoning each within its proper zone of
elevation, as on plain land they were confined
within parallels of latitude. From these
heights the eye wanders over all the climatal
regions of vegetation piled one above the
other; surveying at a single glance the
feathery palm, the tree-fern with lace-
like foliage, the oak, the alpine rose,
the yellow wavy grass-fields, and the
grey lichen. At their base flourish the
banana of the south and the orange:
the lofty peaks are clothed with lichens or
with eternal snow.

It is here that we most clearly recognise
the imperial sway of heat over the
vegetable kingdom. It was on the rocky walls
and declivities of the Cordillera, that
Humboldt first read the laws of heat
indelibly inscribed, and demonstrated to us its
potent influence in effecting the climatal
distribution of organic forms, and in altering the
aspect of nature. It was a considerable step
towards more perfect comprehension of this
subject, when he connected with imaginary
lines those points on the earth which enjoy
the same mean temperature, and found that
such " lines of equal heat " coincide with
lines drawn to indicate the boundaries within
which wheat, maize, rice, the vine, the olive,
and other plants, are capable of successful
cultivation. These lines of equal heat are far from
being parallel to the equator; for local influences
strongly affect the temperature of every part
of the globe; but, to them closely cling the
boundaries of vegetation, loyal to the laws
of heat, and widely wandering from the parallels
of latitude to follow accurately these
devious lines which heat has traced for
them; scorning the regular tracks which
geographers have laid down. Nor does
the plant dare to transgress this limitary
legislation.

    This is the primal contract: these the laws
     Imposed by Nature: and by Nature's Cause.

Heat, however, is not the sole potentate
by whose will the fashions of the earth's
apparel are determined. Minor tyrants
enforce equally stringent limitations; narrowing
yet more the sphere of plant-existence,
and the circle within which plant-migration
is possible. One of these sub-regents, is soil.
The plant indigenous to the chalky cliff,
borne on the wings of the storm to a
rocky granite headland, will as surely perish
as the tropic shrub transported to an