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regions in question, and what is perhaps more extraordinary, than
that which exists between Eastern Asia and Europe, although there
is continuous land communication between these two continents.

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The writer recalls vividly the strangely familiar aspect of the
vegetation of Japan, especially in the island of Yezo, where nearly
all the more conspicuous plants were either the same, or closely
related to common species of the Atlantic states. Such character-
istic plants as the Fox-grape, Poison-ivy, Sumach, Bittersweet
(Celastrus), Sensitive-fern {Onodea sensibilis). Elms, Maples, Beeches,
Oaks, and Magnolias, all closely i*esembling or identical with Eastern
American species, were striking features of the vegetation. Were
these forms also common to our Pacific coast, and extended across
the continent, there would be nothing remarkable in encountering
them in Japan, but most of them are quite wanting in the Pacific
states and the intervening country.

Professor Asa Gray made a. very careful study of the relation of
the Japanese flora to that of North America, and states that over
60 per cent of the Japanese plants are represented in our Atlantic
states by either identidal species or closely related ones. This is
against 37 per cent for Pacific North America and 48 per cent for
Europe. Ninety genera are given as common to Japan and America,
which are absent from Europe, and of these the greater part are also
wanting on our Pacific coast. Among the most characteristic of
these may be mentioned Magnolia, Nelumbo, Ampelopsis, Wistaria,
Hydrangea, Hamamelis, and Catalpa.

A study- of these forms reveals the interesting fact that the trees
are, almost without exception, genera which are represented in the
Tertiary flora of Europe, as well as that of Japan and America, and
it is highly probable that the herbaceous plants, like Dicentra, Podo-
phyllum, Jeffersonia, and other peculiar types of the Asiatic and
North American flora, are also descended from Tertiary ancestors.

The survival of these plants in such widely separated regions is
accoimted for by the topography of the country, which allowed them
to retreat southward during the glacial period, and to reestablish
themselves northward with the increasing warmth. The climatic
conditions of the present are very similar in the two regions, and
are suited to the needs of these plants. Their absence from those
parts of Europe where the climatic conditions are suited to their
growth is due to their complete extinction during the severe glacier-
ation to which all of northern Europe was subjected.

The absence of these from the Pacific coast is readily explicable
from the character of the climate in the warmer parts, which is quite
unsuited to the growth of most of these forms.

The occurrence of the same or closely related species of the same
genus in widely separated regions can also be explained usually as
survivals of a once widespread type. A well-known case is the
genus Torreya, a Conifer of the Yew-family. Four species are now
known, one in Florida, one on the Pacific coast, and two in China

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and Japan. We know, however, that in Tertiary times this was a
compion genus all over the northern hemisphere. The Sequoias of
California, and the Cypresses (Taxodium) of the southern swamps,
are also disappearing remnants of widespread Tertiary genera.

Flora of the United States

The great extent of territory within the United States, as well as
the great diversity of surface, is accompanied by a corresponding
variety in the flora, the distribution of which offers many interesting
problems, and illustrates nearly all types of vegetation.

The unbroken central plains possess a continental climate of the
most pronounced character, with a rapid decrease in rainfall west-
ward. On the eastern seacoast there is abundant rainfall, increas-
ing southward, while on the Pacific slope the reverse is the case.
Finally, the arid central and southwestern plateaus are genuine des-
erts, whose scanty flora is extremely characteristic. The direct con-
nection with the Tropics results in a strong infusion of tropical
types in our southern flora, and the unbroken chain of mountains
on the Pacific slope has been an important highway for the south-
ward emigration of many northern types, including a few Asiatic
forms ; and at the east the Appalachian Mountains have also served
to extend the southward range of many northern species.

Leaving aside the aquatic and strand floras, we may divide the
flora of the United States, roughly, into a forest flora, a prairie flora,
and a desert flora, these merging, more or less gradually, into each
other in some cases.

The Eastern Forest. — The greater part of the country east of the
Mississippi was originally covered with a dense forest, containing an
extraordinarily large variety of deciduous trees, as well as a number
of coniferous ones. This forest, on the extreme north, merges into
the subpolar forest zone, which extends more or less completely
across the whole continent, but hardly reaches the confines of the
United States. Our northern forests, such as those of northern
Michigan and Wisconsin, are characterized by the frequent occur-
rence of the White-pine (Pinus strobris), as well as Hemlocks, Spruces,
and sometimes the Norway-pine (Pinus resinosa). Growing with
these, however, are various "hardwood" trees, especially Sugar-
maples, Beeches, Oaks, etc. Where the Pines predominate, there is
little underwood, and the ground is thinly carpeted with Club-mosses,
Wintergreen, and other, mostly evergreen, trailing plants.

Somewhat farther south, reaching its finest development in the
Ohio Valley and along the Alleghany Mountains, is the great forest
of deciduous trees, with relatively few Conifers, which are often
entirely absent. Here the variety of trees is far greater than in the

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northern forest. Among the predominant trees are various Oaks,
several Elms, Maples, Beech, Walnut, Hickories, Gums (Liquidambar
and Nyssa), Ashes, Tulip-tree, Sycamore (Platanus), Poplar. Far-
ther south appear the Magnolias, Persimmons, Papaw (Asiinina), and
some other sorthem types, which increase as the Gulf of Mexico is
approached. These trees are, with few exceptions, deciduous, and
in the spring the floor of the forest is carpeted with many beautiful
flowers, which pass through their whole growing period in a few
weeks. Of the early flowers especially characteristic of the Ameri-
can forest may be mentioned species of Claytonia, Dicentra, Erigenia,
Sanguinaria, Erythronium, Trillium, Podophyllum, and Jeffersonia,
which are associated with Hepaticas, Anemones, and Violets, much
like those of the European woods.

The deciduous forest is much richer in undershrubs and climbers
than the northern forest, and the number of these increases rapidly
as we proceed southward, where many beautiful flowering shrubs like
the Kalmias, Azaleas, Rhododendrons, Stuartias, Philadelphus, Hy-
drangea, etc., give an added charm to the woods. In these southern
forests, also, the number of climbing plants increases, and gives
a suggestion of the lianas of the Tropics. Clematis, Bittersweet,
gigantic Grapevines, Ampelopsis, Trumpet-creeper, Wistaria, and
other woody creepers cover the trunks of the trees with their gar-
lands of leaves, or clusters of showy flowers.

Autumn gives an additional beauty to these great deciduous forests,
when the Maples, Gums, and other trees display the magnificent colors
of their ripening foliage.

Near the coast, and farther inland southward, are barren sandy
districts, " Pine barrens,'' which are occupied almost exclusively by
Pines (P. palustriSy P, tceda, etc.), but these cover a relatively small
area compared to the great deciduous forests.

Finally, in the extreme south of Florida is a small district where
the forest is almost tropical in its composition, and contains a num-
ber of forms related to the adjacent West Indian types. Palmettoes,
wild Figs, a few epiphytic Orchids and Tillandsias, recall faintly the
exuberant growth of these plants in the neighboring islands of Cuba
and Jamaica.

Prairies. — With the diminishing rainfall westward, the forests of the
Atlantic states gradually give way to the prairies which cover most of
the region between the Mississippi and the base of the Rockies. The
transition is not a sudden one, and in southwestern Michigan, western
Indiana, and Illinois patches of prairie occur in the forested area, or
groves of trees occur scattered over the prairie region. The " Oak
openings " of this region are of this nature. They consist of groves
of somewhat scattered trees, mostly Oaks of several species, with
little or no undergrowth of shrubs. Even these disappear as the

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true prairie region is reached. Here no trees can grow except in the
shelter of ravines or along the beds of streams, where Cottonwoods
and Willows are generally found, even in the arid western part of
the prairie region. The typical prairie consists of various grasses
(e,g. Andropogon, Chrysopogon), which form a continuous turf in the
moister eastern prairies, but in the dry western plains are scattered
in tufts over the bare soil. Of these bunch grasses one of the most
characteristic is the Buffalo-grass {Bulbilis dactyloides).

The eastern prairies are gay in early summer with many beautiful
flowers — Phlox, Dodecatheon, Violets, Verbena, Castilleia, Lithosper-
mum; and later appear the showy Compositse, Silphium, Rudbeckia,
Erigeron, Solidago, Aster, Coreopsis, Gaillardia, etc. Further west-
ward, where the ground has been broken up. Sunflowers (Hdianthus
annuus) appear in countless legions.

Western Kansas, and Nebraska, and eastern Colorado are occupied
by arid plains with sparse vegetation, and approach in the character
of their vegetation the deserts of the far West. Yucca, various low
Cacti, and Sage-brush (Artemisia) suggest the strictly xerophytic
growths of the true deserts.

The great differences in the flora of the same latitude due to
the topography are most strikingly seen in the journey irom New
Orleans to Los Angeles in Southern California. The Gulf region
of Louisiana, with its swampy forests, presents an almost tropical
luxuriance of vegetation. Passing westward across Texas, the dense
forests of the coast soon give way to scattered groves of Pines, eviden(5-
ing the marked falling off in the rainfall, which becomes still more
pronounced in the western part of the state, where there is a prairie
formation with only a scattered growth of stunted trees, principally
the Mesquit (Prosopis). In the early summer these prairies show
many beautiful flowers, several of which are garden favorites, such
as the common Drummond's Phlox, Gaillardia, (Enothera, etc.

Deserts. — Journeying westward, another factor in determining the
vegetation is encountered, the southern extension of the Rocky
Mountains. On the westward side of the divide, in New Mexico
and Arizona, the region is a true desert with a very scant veget^
tion, including a number of most characteristic American types. Of
these the first in importance are the Cacti, which reach their greatest
development here and in the neighboring Mexican highlands. The
strange forms of the giant Cactus {Cereus gigantetis), once seen, are
never to be forgotten. In June, many of the Cacti are covered with
their showy crimson and yellow flowers, and with the magnificent
flower-clusters of the Yuccas, make a very striking floral display.
The Century-plant and other Agaves also occur in this region, but
are more abundant farther south.

Entering California, we cross the desolate Mojave desert, absolutely

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Vegetation on the Mojave Desert of Southern California ; Yucca arborescens, the
most conspicuous feature, accompanied by species of Juniperus. Larrea,
Lycium, Ephedra, and several Grasses. (Photograph by Prof. W. Trelease.)

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barren throughout most of its extent, and with its most conspicuous
plant the fantastic Tree-yuccas (PI. XIII), which occur in scattered
groves in a few places. Any more absolute contrast between the
eastern and western ends of the journey it woxild be hard to imagine.

The Flora of the Pacific Coast

The distribution of the plants upon the Pacific coast, especially in
California, offers most interesting problems to the student of phyto-
geography. Owing to the equalizing influence of the Pacific, and
the position of the mountain ranges, the climate of the whole Pacific
coast is extremely equable, luxuriant forests extending northward in
Alaska to about latitude 60^. At Sitka, in latitude 57^, extreme cold
is unknown, and the annual precipitation is nearly 250 centimetres,
so that the vegetation is almost tropical in its luxuriance. Spruce,
Hemlock, and Cedars, 30 to 50 metres in height, and with trunks 2
to 3 metres in diameter, are met with, and the ground is covered with
an impassable thicket of shrubs and herbaceous plants. Many of
these are northern types common to the whole sub-arctic zone ; but
others are evidently of Asiatic origin, and do not occur away from
the Pacific coast. The commonest tree, the Sitka-spruce (Picea
SitcJieThsis), is said to occur also on the northeast Asiatic coast, and
a number of herbaceous plants are also Asiatic. Of the latter, the
most conspicuous is the common Aroid (Lysichiton KanUchatcense),
which resembles somewhat the Skunk-cabbage of our Eastern states.
Another Asiatic plant is FritiUaria KanUchcUica, belonging to a
genus which occurs in America only on the Pacific slope.

The whole coast, as far south as Puget Sound, is covered with an
extraordinarily heavy forest of coniferous trees which often come
down to the water's edge. While at the far north the Spruce and
Hemlock predominate, in British Columbia and Washington the
Douglas Spruce (Pseudotsuga Douglasii) is the predominant tree.
Here it attains a height of 100 metres or more, and forms the most
important timber tree of the region.

Most of the herbaceous plants of this region are allied to the
common northern species, and in many instances are identical;
but there is a mingling of forms not found farther east, such as
Lysichiton. Violets, Trilliums, Dicentras, White Clover, much like
those of the Northeastern states, are common, and the general
aspect of the woodland flowers resembles that of northern Michigan,
or the Adirondacks.

The high mountain ranges of the northern Pacific coast are continued
southward into California, where they divide into the Sierra Nevada
and the series of Coast ranges. The rainfall diminishes rapidly
southward, and most of California has an absolutely rainless summer.

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The outer range of Coast Mountains, however, especially in the north-
em part of the state, has an extraordinarily heavy winter rainfaU,
and the dense ocean fogs, which prevail all through the dry season,
take the place of rain to some extent. It is upon these outer Coast
ranges that the Redwood {Sequoia sempervirens) grows, the tallest of
all our trees, some specimens reaching a height of nearly 115 metres
(340 feet), with trunks 6 metres or more in diameter. Many of the
northern plants have followed the mountains southward and estab-
lished themselves in the moist Redwood forests. Trillium, Violets,
Erythronium, Fritillaria, and, in the extreme north, Lysichiton and
Linnsea, are found. The Redwood forests cease about 100 miles south
of San Francisco (lat. 38**), and the forests from Monterey southward
are much dryer, with smaller and more scattered trees, mostly Pines.

At Monterey itself are two trees, most interesting as the sole surviv-
ors of their kind. These are the Monterey Pine (Pintis insignis) and
the Monterey Cypress (Cupresms macrocarpa) (PI. XV), which form
scattered forests close to the sea, but are unknown elsewhere. The
Monterey Pine also occurs sparingly at one or two other points along
the coast.

The second great forest region of California is that on the western
slope of the Sierra Nevada, at a height of 1200 to 2000 metres. Here
is perhaps the most magnificent forest of the world. Among giant
Sugar-pines, Yellow-pines, Spruces, Firs, and Cedars, grow the mon-
archs of the American jforests, the "Big-trees," Sequoia gigantea
(PL 1, Frontispiece). This forest is comparatively open and park-
like, and while the large trees are all Conifers, there is an under-
growth of angiospermous trees. Oak, Dogwood, Maple, and some
others, while many beautiful flowering shrubs also occur. Most
beautiful of all is the fragrant Azalea occidentalism which forms
thickets, covered with beautiful rose-tinted white flowers in early

Ascending the mountains, the trees diminish in size, and disappear
entirely at about 3000 metres. On the east side of the mountains,
owing to the very much diminished rainfall, the trees are much
smaller, and the mountains slope into the deserts of Nevada, covered
with Sage-brush and other desert vegetation.

The predominance of coniferous trees in all the forests of the
Pacific coast is remarkable. Nowhere do the deciduous trees form
any considerable element in the forest, although a considerable
number of species occur. These are found either as an undergrowth
of the coniferous forests or along streams, where they do not form
true forests. Most of these trees are related to eastern species, but
many of the characteristic trees of the Atlantic states are quite
absent. There are no Elms, Beeches, Hickories, Magnolias, or Gums
in the western forests, but the number of species of Conifers is very

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Cupressus macrocarpa, growing upon the exposed coast near Monterey. California.
This species is restricted to a few miles of the coast at this point. ( Photograph
by Dr. F. M. MacFarland.)

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much greater. CaJifornia alone has more species of Conifers than
the whole of the United States east of the Rocky Mountains.

Owing to the dryness of the summer, most of the trees and shrubs
in the central and southern parts of the state are markedly xerophytic
in character. The evergreen leaves are small and thick, well fitted
to endure the hot, dry summer. The great valleys are too dry to
allow the growth of forests, but the bottom-lands, and the foot-
hills of the moister valleys, are covered with wide-spreading oaks,
some of which, like the Live-oak {Quercus agrifolia), are evergreen.
The lower mountain slopes and the foot-hills are generally covered
with a dense growth of shrubs, sometimes thorny, and always
difficult to traverse. This " chaparral " is composed of a variety of
shrubs, including species of Oak and Chestnut, but largely composed
of species of Ceanothus, Adenostoma, Poison-oak (Rhus diversilobus)
and Manzanita (Arctostaphylos). Associated with these are many
beautiful bulbous plants like the Washington-lily, Brodiaea, Calo-
chortus, Zygadenus, etc., which are very largely represented in the
Californian flora.

South of the Tehachapi mountains (lat. 35®) the country is much
more arid, and much of Southern California, especially the south-
eastern part, presents genuine desert conditions. Cacti, Yuccas,
Sa^e-brush, and other characteristic desert plants prevail, and, except
when irrigated, the land is quite useless for agriculture.

Constituents of the California Flora. — The position of California,
extending for ten degrees of latitude along the Pacific Ocean, and
absolutely shut off from communication with the eastern United States
by impassable mountains and deserts, has resulted in a flora having
but little in common with that of the Atlantic states. While a good
many northern plants have made their way southward, following the
mountains, few of these reach beyond the middle of the state, where
they are mingled with many types quite unlike any eastern forms,
and which have undoubtedly been derived from the south. It is
from Mexico, and to some degree from western South America, that
the characteristic plants of the open dry valleys and hills of middle
and southern California originally came, although a very large
number of them have become modified into distinct genera and
species. The open valleys and low hills in early spring are ablaze
with a marvellous variety of brilliant flowers, most of which are
quite new to the eastern student. The fiery orange Eschscholtzia, the
pure blue Nemophila, the creamy Platystemon, golden Compositse in
great variety, blue, white, and yellow Lupines, violet Brodiaeas, and
parti-colored Calochortus, form wonderful flower-carpets, whose
beauty must be seen to be appreciated.

These flowers, as well as many others, are either quite unrelated
to eastern genera or represented only by a small number of forms.

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which are to be considered as stragglers from the West. Thus the
genera Mimulus and Castilleia, which are especially numerous in
California, have each a single representative in the Eastern states.

The central part of California is a meeting-ground for the northern
and southern forms. In the Redwood forests of the Coast range, the
northern Violets, Trilliums, and Fritillarias flourish, and not infre-
quently follow the deep shady canyons almost to the level of the
valley, where they meet the southern Poppies and Lupines.

Some of the commonest of the valley plants are not natives, but
are importations, like most of the common roadside plants of the
East. The Wild-oats {Avena fatua), which covers the foot-hills of
many Californian valleys ; the " Filaree " (Erodium), and the Bur-
clover (Medicago denticulata), which are the commonest of weeds, are
all emigrants from the South of Europe, probably arriving with the
first Spanish settlers, but succeeding better in holding their own in
the new country in their competition with the natives and with other


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the North American Flora to that of South America. Science. 1900.

'01. 2. The Ecological Relations of the Vegetation of Western Texas.

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Chapman. Flora of Southern United States. Cambridge, Mass., 1897.
Clements, F. E., and Roscoe, P. Phytogeography of Nebraska. Lin-
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Coulter, J. M. Flora of the Rocky Mountains. New York, 1885.
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Engler and Prantl. Nattirliche Pflanzenfamilien.
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Scientific Papers. Boston, 1889.

Hitchcock, A. D. Ecological Plant Geography of Kansas. Trans.

Acad, of Sc, St. Louis, VIII. 1898.
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Potoni6, H. Lehrbuch der Pflanzenpalaeontologie. Berlin, 1899.
17. Sargent, S. C. Silva of North America. Boston and New York,
'98. 18. Schimper, A. F. W. Pflanzengeographie. Jena, 1898. (Includes

full bibliography.)
W. 19. Scott, D. H. Studies in Fossil Botany. London, 1900.
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'91. 21. Solms-Laubach, H. Count. Fossil Botany. Oxford, 1891.

22. Ward, Lester F. Many papers on fossil plants, mostly published in
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Abies, 338, ^0, 341, 343.

Abietineee, 332, 339, 340, 343.

Abietinn, 336, 313.

Absorption, of water, 467 ; of food, 499.

Acacia, 22, 409. 434, 503, Fig. 471; A,

^hxrocepkala, 527, Fig. 493.
Acanthaceffi, 459.
Acantbinese, 459.
Accessory pigments, 49, 472.
Acer, AceraceaB, 436, 437, 449, 467, 537;

A. saccharinunit Fig. 428; A, dasy-

carpum. Fig. 428.
Acetabolaria, 113, 115.
Achene, 368.

Achlya, 154, 155; A, Americana, Fig. 119.

Online LibraryDouglas Houghton CampbellA university text-book of botany → online text (page 45 of 50)