Western Reserve chronicle. [volume] (Warren, Ohio) 1855-1921, 1871-02-15
The North American Desert Flora Be.
tween 32o and 42o, North Latitude.


tween 32' and 420, North Latitude.
The following paper was read at the
meeting 1s7O) of the British Associa-
tiOn at Liverpool, England, by C. C.
Parry, NJ. D., the botanist of this De-
partment:
The desert tracts Of North America,
as at present defined by our recent
geographical knowledge, comprise
those interior basins Of greater or less
extent shut In by mountain ranges
from the influence Of the moist ocean
ic currents. These well marked dis
tricts, while presenting certain diver
sities Of soil corresponding to particu-
lar geological conditions, everywhere
characterized by an arid climate,
Irregular and seanty rainy seasons,
and wide extremes Of heat and cold,
both diurnal and annual. The per-
manent water courses Of this region,
having their distant sources in snow
clad SUBMITS, traverse q succession Of
basins, presenting occasional alluyial
belts bounded by elevated and abrupt
table-land, which latter is mainly
composed Of beds Of coarse gravel or
drifting sand. The intervening ridg-
es forming the basin rims are cut
through by those deep ehasms known
as eanOns.
The local drainage, but connected
with the main valleys, terminates
rather in salt lakes or saline fats, the
Intense evaporation being sufficient
to carry OF the superficial supply Of
water, leaving their soluble mineral
contents to be concentrated In the
lower depressiOns. The intervening
rocky ridges and isolated mountain
peaks, when not Of sufficient elevation
% act as eOndensers Of the upper cur
rents Of the atmosphere, exhibit the
same characters Of arid vegetation,
though comprising larger proportion
Of shrubbeFy and dwarf-tree growth.
One Of the most striking features of
the desert flora may be noted in the
very marked distinction between the
annual and perennial vegetation.
Thus, the annual desert plants, whose
period Of growth is strictly confined
to short and uncertain period Of
spring or faH rains, require for their
continued preservation a safe deposit
for their usually minute seeds during
the prolonged dry season. This con-
ditiOn is, in q great measure, supplied
by the porous sandy and gravelly
soil, or rock creviees, into which they
fall and are safely buried, not only
out Of the reach Of climatic influences,
but also safe from destruction by ami
mails Their growth is necessarily
rapid and evanescent, and no sooner
do warm rains mOisten the ground
than they spring forth from their
hiding places and elOthe the barren
soil with their seanty verdure, rapidly
flower and mature their seeds, which
are again deposited in the earth,
while their slight eyanescent forms
dry up and are blown away, hardly
leaving any visible trace Of their ex-
istence. These characteristics are
plainly exhibited in ordinary herbar-
ium specimens, and are further ex-
emphfied in the specific name Of
exile" 50 often very appropriately
applied. On the other hand, the per-
ennial desert plants either store up a
large amount Of surplus ROurishment
in their thick, tuberOus, or tap roots
or, in the case Of trees and shrubs,
present exposed stems and foliage Of
the most scant and starved character.
Spine-clad branches and green-bark-
ed stems are, in many instances,
made to supply the ONCE Of leaves, or |
where these latter are present, they
are often thiekly coated with resinous
varnish, or clothed with tomentOse
hairs or scales, serving, in either case,
70 check evaporation, and thus limit
the usual processes OF growth. The
preservation Of species in perennial
plants being less dependent than in
annuals on the production Of seeds,
these are generally scanty, often ma
ture late, and are frequently protected (
by hard or spiny envelopes. In GER
tain cases, especially among cactuses,
proliferous shoots, easily detached
and quickly roofing, serve the pur-
pose Of seeds in providing for the col
tinuance and distribution Of species;
and in such instances the very re-
markable and significant fact may be
noted, that the fruits generally prove
abOrtiye, or even revert to the eondi-
ton Of prOliferous shoots.