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THE GEOGRAPHIC SOCIETY OF CHICAGO
Butuetin No. 2

THE PLANT SOCIETIES OF
CHICAGO AND VICINITY

BY

HENRY C. COWLES

. aX
Associate Professor of Plant Ecology, the University of Chicago

PUBLISHED FOR THE GEOGRAPHIC SOCIETY OF CHICAGO
BY
THE UNIVERSITY OF CHICAGO PRESS
CHICAGO, ILLINOIS

AGENTS
THE BAKER & TAYLOR COMPANY, New York
THE CAMBRIDGE UNIVERSITY PRESS, London and Edinburgh

Ke

Published rgorz

PREFACE

This bulletin is designed to accompany the first bulletin of the
Chicago Geographic Society by Prof. Rollin D. Salisbury and Mr.
William C. Alden, and in many places it is assumed that the geographic
features of the Chicago area, as there outlined, are known to the
reader. The matter here presented has been gathered by the author
in the course of the past five years, and has recently been published in
the BoranicaL GaZETTE, essentially as presented here.

The author desires to express his indebtedness to Mr. W. B.
McCallum, who has taken most of the photographs with which this
paper is illustrated. These illustrations, by common agreement, have
also appeared in the BoTanicaL GazETTE. igs. 7 and 73 were con-
tributed by Prof. J. J. Allison of Joliet. igs. 34, 35 and 36 have been
previously published by the author. The map shown in fg. 379 appeared
in the first bulletin of the Chicago Geographic Society.

OUTLINE

INTRODUCTION

THE PLANT SOCIETIES.

A. THE INLAND GROUP.

1, THE RIVER SERIES.
a. The Ravine:
b. The River Bluff.
c. The Flood Plain.

2. THE POND-SWAMP-PRAIRIE SERIES.
a. The Pond.
b. The Undrained Swamp.
c. The Prairie.
3. THE UPLAND SERIES.
a. The Rock Hill.
b. The Clay Hill.
c. The Sand Hill.

B. THE COASTAL GROUP.

1, THE LAKE BLUFF SERIES.
2. THE BEACH-DUNE-SANDHILL SERIES.
a. The Beach.
b. The Embryonic or Stationary Beach Dunes.
c. The Active or Wandering Dunes. The Dune Complex.
d. The Established Dunes.

APPENDIX.—THE PRINCIPAL LOCALITIES ABOUT CHICAGO FOR THE
Stupy OF PLANT SOCIETIES.

INTRODUCTION.

In recent years a great impulse has been given to the study of
plants in their environment by the works of Warming, Schimper, and
other European botanists. The subject that deals with this part of the
botanical field is now called plant ecology—the science of plant house-
keeping, or, as some would say, plant sociology. One phase of ecology
deals with the meaning of plant structures, such as leaves, roots, flow-
ers; the variation of these organs is investigated in relation to the
influence of external agents, and attempts are made to work out the
causes which determine plant forms. This phase of the subject is
presented in Kerner and Oliver’s Natural History of Plants and in Dr.
Coulter’s Plant Relations.

A second phase of ecology, and the one that concerns us here, has
to do with plants not as individuals, but as grouped in societies. Very
superficial observation shows that certain plants grow in swamps, others
in forests, and still others on sand dunes. Warming, in his Ecological
Plant Geography, published at Copenhagen in 1895, gave the results
of a long series of investigations as to the causes determining these
diversities in the distribution of plants. He divided the plants of the
world into four great groups: hydrophytes, or plants which grow in
water or wet places ; xerophytes, or plants which grow in dry habitats ;
mesophytes, or plants which grow in places of medium moisture, such
as ordinary forests and meadows; and halophytes, or plants which
grow in salt-water or alkaline soil. It will be seen that all of these
groups except the last are related to water, which is commonly re-
garded as the most important factor in determining local differences in
plant societies. Most botanists have accepted Warming’s classification
of plant societies as a more or less complete organization of this part
of the ecological field.

The present paper attempts to relate the plant societies not
only to water, but also to soil, and more especially to the physi-
ography. The geographic and ‘physiographic features of the Chi-
cago region have been admirably presented in papers by Leverett,’

1LEVERETT, F.: The Pleistocene features and deposits of the Chicago area. Chicago.
1897.
Hf

8 INTRODUCTION.

and Blatchley,! and more recently in a bulletin of the Chicago
Geographic Society by Salisbury and Alden.” As the map shown
in Fig. 39 indicates, the topographic and soil areas in the vicinity
of Chicago are of three types: morainic deposits, chiefly bowlder
clay; the Chicago plain, representing the area covered by the glacial
Lake Chicago; and beach or dune sands, connected with the present
or former beach lines. Speaking generally, the Chicago district has
three great vegetation types connected with these three soil and.
topographic types: the mesophytic upland forests of the morainic
clays, the hydrophytic lakes and swamps or mesophytic prairies of
the Chicago plain, and the xerophytic forests of the dunes and
beaches.

A close analysis shows that the types of plant societies are numerous
in each of the three general areas named above. In the morainic
areas there are several forest types, as will be shown in the body of the
paper, and it is here that the various phases of stream activity with
their characteristic plant societies are best seen. The types of vegeta-
tion on the plain are fewer, including in the main only the various
transitions between ponds, swamps, and prairies. The ancient beach
lines present some, but not much variety, but the dune area of the
present beach line presents a rich diversity of plant societies.

The keynote of this paper is that each particular topographic form
has its own peculiar vegetation. This is due to the fact that the soil
conditions upon which plants depend are determined by the surface
geology and the topography. From the standpoint of the vegetation
the topographic relations are more important than the geological. As
will be shown later, all kinds of soils may have the same vegetation
when placed in similar topographic conditions, whereas the same soil
may show many diverse types of vegetation. The topographic condi-
tions determine the exposure, tNe presence or absence of drainage, and
the humus content of the soil, and are thus of overshadowing im-
portance.

Having related the vegetation largely to topography, we must rec-
ognize that topography changes, not in a haphazard manner, but ac-
cording to well-defined laws. The processes of erosion ultimately

1BLATCHLEY, W.S.: The geology of Lake and Porter counties, Indiana. Reprint from

the Twenty-second Annual Report of the Department of Geology and Natural Resources of
Indiana. Indianapolis. 1897.

*SALISBURY, R, D., and ALDEN, W. C.: The geography of Chicago and its environs.
Chicago. 1899.

EXCURSION BULLETIN NO. 2

PRICE 10 CENTS

THE

GEOGRAPHIC SOCIETY
OF CHICAGO

EXCURSION ON THE ROCK RIVER OF ILLINOIS
BETWEEN ROCKFORD AND DIXON

PREPARED OCTOBER, 1911

BY

MR. R. E, BLOUNT, Leader

oo

PORTION OF THE ROCK AND PECATONICA RIVERS, ROCKFORD,
NEW MILFORD, BYRON, OREGON, GRAND DETOUR, DIXON

PRE-GLACIAL STREAMS, CONJECTURAL

ROCK RIVER

HE most picturesque portion of Rock River lies between Rockford and
T Dixon. From Rockford north the river lies in a pre-glacial valley.

A few miles south of Rockford, the river abandons its old valley
(which runs nearly south and is largely filled with glacial debris), and takes
a new course ina southwest direction. This new course in places coincides
with the valleys of pre-glacial streams, and in places cuts across old divides.
In the former instances, the presént valley is broad, a mile more or less,
with gently sloping sides; in the latter, the valley is narrow with precipitous
slopes. The wooded bluffs, in places picturesquely carved by rain wash,
are the most attractive features of the region. From their crests long vistas
of the river reach away to the open valley, with its cultivated slopes.

HISTORICAL

The rock of this region is Ordovician, for the most part Galena-Trenton
dolomite, with a strip of St. Peters sandstone outcropping from a point
near Oregon to a point south of Grand Detour, and a small area of Lower
Magnesian limestone south of Oregon. This whole section probably had
been base-leveled, the streams rejuvenated, and the valleys developed about
to maturity in pre-glacial times. The glacial incursions carried away the
mantle rock, and the upper part of the bed rock, and spread a covering of
glacial drift over the surface. This drift (2//) covering smoothed off the
irregularities of contour of the solid rock surface, and is adequate for an
arable soil; at the same time that it does not completely fill the valleys,
leaving the drainage good. There are very few acres of waste land. The
latest ice-sheet which overspread this region was much older than the last
one which covered the region about Chicago. While the northeastern part
of the state was covered with the last ice-sheet, this area was exposed.
The earlier glacial drift was decomposing, in preparation for the rich soil of
the rolling prairies. Streams were cutting their valleys in the glacial drift
and into the underlying rock. The present valley of Rock River was
nearly as large as now when the Late Wisconsin ice-sheet invaded the state.
Thru the valley poured the floods of water from the later glacier, carrying
an immense load of sand and gravel, much of which was deposited, partially
filling the valley. This filling of gravel and sand is usually topped by a
few feet of clay and loam. Since the glacial period, the river has sunk its
valley in these fills to a depth of 25 or 80 feet, leaving the parts which
still remain as level, well drained terraces with arich soil. On the terraces
the first settlements sprang up, and they are the sites of most of the villages
and cities along the river.

LOCAL NOTES

“The Bluffs.”. Abaut two and a half miles north of Byron the river
has cut thru a pre-glacial divide, forming the best gorge in its whole course.
On the west side the dolomite rocks rise precipitously though pretty. well
screened by. the trees on the talus, which is sometimes washed by the spring
floods. The east side is well covered with forest, with here and there a
ledge of rock outcropping. The bluff is well marked for only about half a
mile, but extends to the north much farther, lying back many rods from
the present channel of the river. . The most picturesque of the several
ravines cutting the bluff is the most southerly, lying about one-eighth of a
mile from its south end. It is shady, cool and damp, even on the hottest
summer days. Before the upland timber was cleared off to make room for the
plow, there were several delightful springs which supplied a perennial stream
down this gorge, whose bed is now dry much of the year. A salient rock,
easily reached from above or below, locally known as Black Hawk’s pulpit,
stands near the middle of the principal bluff. The view to the north and
south from the crest of the bluff is worth not only the climb from the road,
but a journey of many miles.

The Gravel Fill. In later glacial times, the water rushing thru the
gorge at The Bluffs carried a load of coarse sediment which it was com-
pelled to drop when it spread out in the broad pre-glacial valley to the
south. This formed the terrace on which the village of Byron is situated.
The gravel beds are highest near the mouth of the gorge, and fall away at
a scarcely noticeable rate down stream. In places they are scantily covered
with soil. In the village they are covered with several feet of clay, topped
with a rich loam. In the gravel pit of the Great Western Railway, the
details of the structure of river deposits—cross-bedding, stratification, etc.,
can be well studied. The gravel pit is replacing the stone quarry in these
days of cement construction. ,

The Galena-Trenton Rock. The glaciers that passed over this region
removed the weathered rock, leaving the firm rock surface covered with till.
Here and there on places of considerable slope the rain-wash has removed
the clay, sand and gravel, leaving occasional bowlders perched on the bed
rock. Where the drift has been removed, the bed rock has been shattered
by changes of temperature to a depth of a few feet, below which the firm
rock appears. These exposed places are most convenient for opening
quarries. Before the common use of cement in construction, the quarries
supplied the surrounding country with stone, and some of it was shipped
forty or fifty miles to the east. Now the quarries are seldom worked.
The rock is compact, stands the weather fairly well, and can be burned for
lime. It contains abundant fossils—corals, crinoids, cephalopods, etc.
Specimens of Orthoceras four or five inches in diameter have been found.

The Big Spring. About two miles southwest of Byron, from a rock
crevice at the foot of a hill washed by the river in flood, gushes a little
stream of clear, cool water. This spring is typical of those that abound in
limestone regions. It is one of the few still surviving the destruction of
the forests which once covered the uplands bordering the river. It has
shrunk to less than half its former volume, and its companion springs a few
rods on either side have disappeared entirely. The spring is fed by the
_.rain water which seeps down thru the soil and collects in the cracks of the
rock. The cracks are enlarged by the slow dissolving of their sides, till
an underground system of channels is formed. The deforestation of the
land results in a rapid run-off of the rain, and robs the spring of its water

supply.

Ganymede and Black Hawk. Half a mile to a mile north of Oregon
the river cuts thru another pre-glacial divide, forming high, steep valley
sides, in places with outcropping rock. A number of Chicago artists have
built cottages on the crest of a bluff above a fine spring, and spend their
summers here. A few feet away and a little lower than the spring, they have
built a masonry basin to form a bathing pool for those who like a cold plunge.
Tradition has it that years ago Margaret Fuller, traveling thru the wild
west, named this spring Ganymede, and under the gnarled cedars at the
top of the bluff wrote the verses ‘“Ganymede to his Eagle’. In honor of
this noted woman, the island lying near the bluff is called Margaret Fuller
Island. A heroic statue of Black Hawk, the work of Lorado Taft, crowns
the hill, and ever gazes in dignified contemplation down the valley once
dear to his vanished race.

Oregon, like the village of Byron, is situated on a terrace of sand and
gravel, the material of which was derived from the ice of the Wisconsin
glacial epoch. The pre-glacial valley in which the terrace lies extends to
the southeast, and seems to have headed in the hills west of the city. Be-
tween Oregon and Grand Detour are several places where the water of the
river is shallow, and its gradient steep, making navigation difficult in low
water. There is here a large amount of water-power going to waste. Resi-
dents have little doubt that as this region develops, there will be one or
more dams built between Oregon and Grand Detour, as well as at Byron,
and the power used for lighting or manufacturing, as is now done at Oregon,
Dixon and other cities on the river.

Castle Rock. About five miles below Oregon the river, probably cutting
thru another ancient col, is flanked by bold headlands of St. Peter’s sandstone.
The contrast with: the limestone bluffs farther north is striking. The white
and tawny sandstone is less resistant to the weather and is more fancifully
carved by the rain. Its waste supports a vegetation markedly different
from that on the rich limestone soil. A number of miles to the north is a
considerable growth of white pine, not found elsewhere in Illinois. Visitors
who have been along the Illinois River from Ottawa to La Salle will recog-
nize the kinship to this area, a likeness depending on the same underlying
rock.

Grand Detour. The big bend in the river is the seat of a village once
flourishing and hopeful of great manufacturing development; now dormant
and consoling herself by the enterprise of two hotels, fairly well patronized
by summer visitors. A wing dam, now fallen into decay, threw the current
of the river to the right bank, where it was caught in a canal, and conducted
by a short cut across the bend. Thus power was obtained for driving the
factory wheels. A generation ago Grand Detour plows were familiar to the
Illinois farmer. The factory burned. The concentration of capital at
Rockford, Moline, Chicago and elsewhere was more efficient in building up
extensive industries than the natural advantages of water-power. Therefore
Grand Detour sleeps. In the bend and for a few miles down stream are
beautiful rocks of St. Peter’s sandstone jutting into the stream, White
Rock, Whirlpool Rock, Pine Point, etc.

Dixon, like the other towns along the river, is situated on a terrace in
a pre-glacial valley, and just. below a cut through an old divide. It is the
center of a rich farming region and has considerable small manufacturing.
The largest industry is the cement works, just above the town. The fall
in the river is used in generating electricity. The deep water above the
dam gives opportunity for much pleasure boating, and the beautiful groves
bordering the stream afford delightful picnic grounds.

INTRODUCTION. 9

cause the wearing down of the hills and the filling up of the hollows.
These two processes, denudation and deposition, working in harmony
produce planation; the inequalities are brought down to a base level.
The chief agent in all these activities is water, and no fact is better es-
tablished than the gradual eating back of the rivers into the land and
the wearing away of coast lines; the material thus gathered fills up
lakes, forms the alluvium of flood plains, or is taken to the sea. Vege-
tation plays a part in all these processes, the peat deposits adding
greatly to the rapidity with which lakes and swamps are filled, while
the plant covering of the hills, on the contrary, greatly retards the
erosive processes. Thus the hollows are filled more rapidly than the
hills are worn away. As a consequence of all these changes, the slopes
and soils must change; so, too, the plant societies, which are replaced
in turn by others that are adapted to the new conditions.

There must be, then, an order of succession of plant societies, just
as there is an order of succession of topographic forms in the chang-
ing landscape. As the years pass by, one plant society must necessa-
rily be supplanted by another, though the one passes into the other by
imperceptible gradations. One thing more must be recognized, and
that is that environmental influences are normally cumulative. A plant
society is not a product of present conditions alone, but the past is
involved as well. For example, a hydrophytic plant society may be
seen growing in a mesophytic soil; the author has seen a mesophytic
tamarack swamp which can be explained only in this way. We have
in this phenomenon a lagging of effects behind their cumulative
causes, just as the climax of the heat in summer comes long after the
solstice.

In a classification like this great emphasis is placed on border lines
or zones of tension, for here, rather than at the center of the society,
one can best interpret the changes that are taking place. Of course
the order of succession referred to above is a vertical or historical one.
One plant society is said to follow another if it is actually superimposed
upon the one preceding. In many cases, if not in most, there is a
horizontal order of succession at the present time that resembles the
vertical succession of which we now have only the topmost member.
Instances of similarity between vertical and horizontal orders of suc-
cession are well shown in peat swamps and along shores and flood
plains. Along a sandy shore it is only by studying the horizontal suc-
cession that one can get any idea of the vertical, since all fossil traces

10 INTRODUCTION.

of preceding plant societies have passed away. In peat swamps
one can sometimes verify the results of a horizontal zonal study by
investigating the fossil remains beneath.

We may now outline the main features of a physiographic classifi-
cation of plant societies. Speaking in the large, the tendency of the
erosive processes is to reduce the inequalities of the topography and
produce a base level. This base level may not soon be reached,
though geological history furnishes instances of extensive base level-
ing. Crustal movements interfere with the erosive agencies, and a
mature base level topography may become rejuvenated by a great up-
lift of the land, or sinking, on the other hand, may check the rapid
action of erosion. Yet even with the crustal movements there go these
topographic changes, and with them the plant societies must change.
Putting the facts of physiography in the terms of ecology, the con-
ditions become more and more mesophytic as the centuries pass. In
a young topography such as the recently glaciated areas of Michigan,
Wisconsin, and Minnesota, there is a great variety of topographic con-
ditions and of plant societies. Among these are many hydrophytic
lakes and swamps and many xerophytic hills. The hills are being
denuded and the swamps and lakes are being filled, so that the hydro-
phytic and xerophytic areas are becoming more and more restricted,
while the mesophytic areas are becoming more and more enlarged. In
passing from youth to old age, then, a region gradually loses its hydro-
phytic areas, and also its xerophytic areas, though in the latter case
there is usually at first an increase in the xerophytic areas, which is due
to the working back of the young streams into the hills. These latter
conditions are well shown in Iowa; in the comparatively recent Wis-
consin drift of northern central Iowa the topography is much less
diversified and there are fewer xerophytic areas than in the older
Iowan drift farther south, which has been greatly dissected by stream
erosion. Later, however, the inequalities are removed and we find
great mesophytic flood plain areas, such as are seen along the lower
Mississippi.

From what has been stated it will be seen that the ultimate stage
of a region is mesophytic. The various plant societies pass in a series
of successive types from their original condition to the mesophytic
forest, which may be regarded as the climax or culminating type.
These stages may be slow or rapid; some habitats may be mesophytic
from the start; undrained lakes and swamps fill up and become meso-

INTRODUCTION. II

phytic with great rapidity, whereas granite hills might take many cen-
turies, or even geological epochs, in being reduced to the mesophytic
level. Again, the stages may be direct or tortuous; we have already
seen how the first consequences of stream erosion may be to make
mesophytic areas xerophytic. So, too, in flood plains, the meander-
ings of the river may cause retrogressions to the hydrophytic condition
such as are seen in oxbow lakes, or the river may lower its bed and the
mesophytic flood plain become a xerophytic terrace. But through all
these changes and counterchanges the great mesophytic tendency is
clearly seen; mesophytic areas may be lost here and there, but many more
are gained, so that the approach to the mesophytic base level is unmis-
takable. Moreover, the retrogressive phases are relatively ephemeral,
while the progressive phases often take long periods of time for their
full development, especially in their later stages. The statements
made in this paragraph have reference only to such regions as the one
in which Chicago is located. In desert regions, and also in arctic or
alpine districts, the ultimate stage cannot, of course, be mesophytic
under the present climatic conditions.

THE PLANT SOCIETIES.

A. THE INLAND GROUP.
1. THE RIVER SERIES.

A. The ravine.—No topographic forms lend themselves so well

to a physiographic sketch of the vegetation as do those that are con-
nected with the life history of ariver. Beginning with the ravines,
which are deep and narrow, because of the dominance of vertical cut-
ting, we pass to the broader valleys, where lateral cutting becomes
more pronounced. From this stage on we have to deal with two phases
of river action, the destructive, which is concerned with the life history
of the bluff, and the constructive, which has to do,with the develop-
ment’of the flood plain.
Wherever there is an elevated stretch of land adjoining a body of
watery. such as a lake bluff, one is apt to find excellent illustrations of
the beginning of aravine. Fig. 7 shows an embryonic ravine of a
type ‘that may be seen frequently along the clay bluffs between Evans-
ton and Waukegan. A ravine of this type is essentially a desert, so
far as plant life is concerned. The exposure to wind and to alterna-
tions of temperature and moisture is excessive. The lack of vegeta-
tion, however, is due chiefly to the instability of the soil; this
instability is particularly great in the case of clay bluffs such as these,
where the seepage of water causes extensive landslide action. No
plants can get a foothold in such a place, unless it be a few species
that may be able to make their appearance between periods of land-
slide action ; among these plants annuals particularly predominate.
The perennials that may be found in such places are almost entirely
plants which have slid down the bank. Near the center of fig. 7 is a
clump of shrubs that have slid down in this way. Ravines of a similar
type may also be seen at many places inland, and wherever found the
poverty of vegetation on the slopes is the most striking character.

As a ravine extends itself inland the conditions outlined above
may be always seen about its head, but toward the mouth of the ravine
the slopes are less precipitous. Torrents cut down the bed -of the
ravine until a depth is reached approaching the water level at its mouth.

13

14 THE PLANT SOCIETIES OF

From this time on the slopes become reduced and the ravine widens
more than it deepens, by reason of lateral cutting, landslide action,
and side gullies. After a time a sufficient stability is reached to per-
mit a considerable growth of, vegetation. If the erosion is slight
enough to allow a vegetation carpet to develop, a high degree of

Fic. 1.—Embryonic ravine in the lake bluff at Glencoe. Entire absence of vegetation on the
unstable clay slopes, with the exception of shrubs and grasses that have slid down from the top.

luxuriance may be attained. In fact, ravine conditions are usually
extremely favorable for plants, after the initial stages have passed. In
a comparatively few years the vegetation leaps, as it were, by bounds
through the herbaceous and shrubby stages into a mesophytic forest,
and that, too, a maple forest, the highest type found in our region.
Nothing shows so well as this the brief period necessary for a vegeta-
tion cycle in a favored situation as compared with an erosion cycle.

Of such interest are the facts just noted that it is worth while to
mention some of the characteristic ravine plants. Perhaps the most
characteristic trees of the Glencoe ravines are the basswood (7ika
Americana) and the sugar maple (Acer saccharinum), though the ash,
elm, and other trees are trequent. The most characteristic under-

CHICAGO AND VICINITY. 15

shrub is the witch hazel (Hamamelis Virginiana). The herbaceous
plants are notoriously vernal forms, such as Hepatica, Thalictrum,
Trillium, Mitella, Dicentra, Sanguinaria (Bloodroot); mosses abound
and liverworts are frequent. A ravine with the above vegetation is
shown in fig. 2. Wecan explain this flora only by regarding it as

at

Fic. 2.—Ravine at Glencoe wi.h a mesophytic forest vegetation on the slopes (temporary
climax). Presence of erosive forces indicated by leaning trees. Water commonly present in
the stream bed.

having reached a temporary climax. Ravine conditions are more
favorable for plants than those that precede or follow. .The instability
and exposure of the gully have gone; in their place there is protection
from wind and exposure. The shade and topography favor the collec-
tion and conservation of moisture, and as a result there is a rapid
development into a high-grade forest, as outlined above.

Rock ravines are much less common in the Chicago area than are
those of clay, since the underlying limestone rarely comes near the
surface. Excellent illustrations of stream gorges are to be seen at
Lockport, and also in various tributaries of the Illinois river near
Starved Rock. A striking difference between these rock gorges or

16 THE PLANT SOCIETIES OF

cafions and the clay ravines is in the slope of the sides. The physical
nature of the rock excludes landslide action, hence the sides are often
nearly vertical for along time. Lateral cutting is also relatively slow
as compared with clay. Thus the conditions for vegetation at the
outset are much more favorable than in a clay ravine. Rock-bound

Fic. 3.—Head of a cafion in the St. Peters sandstone at Starved Rock. Erosive forces
prominent, and vegetation slight on the dripping slopes.

gorges are very shady and often dripping with moisture, hence liver-
worts and many mosses find here a habitat even more congenial than
in the clay. Among the higher forms are found the most extreme
shade plants that we have, such as Impatiens, Pilea, and shade-loving
ferns, plants whose leaves are broad and remarkably thin. igs. 7 and
4 represent cafions of the above description, whose rocks drip with
moisture.

The stages of development pass much more slowly in cafions than
in clay ravines, largely because the primitive conditions of shade and
moisture remain for a long period of time. Nor do the steep slopes

: CHICAGO AND VICINITY. 17

permit the development of a wealth of trees and shrubs, since a secure
foothold is not easily found. However, as the cafion broadens out
and the slopes become less steep, shrubs and trees come in, though a
typical mesophytic forest is rarely seen. The Starved Rock ravines
are cut in St. Peters sandstone, those at |.ockport in the Niagara lime-

Fic. 4.—Side of a cafion in the St. Peters sandstone at Starved Rock. Herbaceous shade
vegetation on the precipitous slopes.

stone, yet the vegetation in the two places is essentially alike; at any
rate, the resemblances are greater than the differences. Much has been
written on the physical and chemical influences of rocks upon the
vegetation. The facts seen here seem to show that the physiographic
stage of a region is more important than either. The flora of a youth-
ful topography in limestone, so far as the author has observed, more
closely resembles the flora of a similar stage in sandstone than a young
limestone topography resembles an old limestone topography. A

18 THE PLANT SOCIETIES OF

limestone ravine resembles a sandstone ravine far more than a lime-
stone ravine resembles an exposed limestone bluff, or a sandstone
ravine resembles an exposed sandstone bluff. We may make the above
statements in another form. Rock as such, or even the soil which
comes from it, is of less importance in determining vegetation than
are the aerial conditions, especially exposure. And it is the stage in
the topography which determines the exposure.

All of the preceding statements as to topographic stages, whether
young or old, refer not to times but to constructional forms. Two
ravines, equally youthful from the topographic standpoint, may differ
widely as to actual age in years or centuries, since erosion is more
rapid in one rock than in another. In our region, however, elements
of actual time are not very important, except as between rock and clay,
since the limestone is less soluble and the sandstone is more easily
eroded than is often the case. :

B. The river bluff-—As a valley deepens and widens, the conditions
outlined above undergo radical changes. From this point it will be
necessary to discuss two phases in the growing river, the bluff phase
and the bottom phase. We have left the clay ravine bluffs in a state
of temporary climax, clothed with luxuriant mesophytic forest trees
and with a rich undergrowth of vernal herbs. More and more the
erosive processes are conspicuous laterally, and widening processes
prevail over the more primitive deepening. As a result, the exposure
to wind, sunlight, and changes of temperature increases; the moist-
ure content of the slopes becomes less and less. The rich meso-
phytic herbs, including the liverworts and mosses, dry up and die.
The hamus oxidizes more rapidly, and a xerophytic undergrowth
comes in. In place of Hepatica and its associates, we find Antennaria,
Poa compressa (Wire grass), Eguisetum hyemale (Scouring rush), and
other xerophytic herbs; Polytrithum also replaces the mesophytic
mosses. ‘The first signs of the new xerophytic flora are seen at the top
of the ravine slope ; indeed, the original xerophytic plants may never
have been displaced here by the ravine mesophytes. As the ravine
widens, the xerophytic plants creep. down the slope, often almost to
the water’s edge. Some of the young ravines between Evanston and
Waukegan show xerophytes at the summits of the slopes. ig. 5
shows a widening ravine at Beverly Hills; the vegetation is much less
luxuriant than that shown in the young ravine of fig. 2.

After a few years have passed, xerophytic shrubs appear on the

CHICAGO AND VICINITY. 19

bluff in place of the witch hazel and its associates. And it is not long
until xerophytic or semi-xerophytic thickets prevail, in place of the
former mesophytic undershrubs. Among the more characteristic of
these shrubs are the hop tree (P%elea trifoliata), bittersweet (Celastrus
scandens), sumachs (Rhus typhina and R. glabra), chokecherry

Fic. 5.—Open ravine at Beverly Hills, showing gentle slopes covered with a less mesophytic
vegetation than is shown in fg. 2. Dominance of oaks in place of maples and basswoods.

(Prunus Virginiana), nine-bark (Physocarpus opulifolius), wild crab
(Pyrus coronaria). Two small trees are common on stream bluffs, the
service berry (Amelanchier Canadensis) and the hop hornbeam (Os¢rya
Virginica); this last species is perhaps the chief character tree of river
bluffs, and is rarely absent. Perhaps the best examples of xerophytic
streain bluffs near Chicago are along Thorn creek. One of the most
interesting things about these bluff societies is the frequent presence
of basswoods and sugar maples. Doubtless these trees look back to
the mesophytic associations that have otherwise disappeared. As
would be expected, the last of the mesophytes to die are trees, because
they are longer-lived than herbs and shrubs, and also because their
roots reach down to the moisture. But they cannot be succeeded by

20 THE PLANT SOCIETIES OF

their own kind, inasmuch as the critical seedling stages cannot be
passed successfully.

The life history of the rock ravines, or cafions, is somewhat differ-
ent. When the ravine vegetation is at its height, the moisture and
shade are greater here than in the clay, hence the high development of

Fic. 6.—Xerophytic bluff of St. Peters sandstone at Starved Rock on the IJIlinois river, show-
ing conifers and other plants of dry rocks. Influen:e of erosive forces seen at the base.

liverworts and their associates. As the ravine widens, these extreme
shade forms are doubtless driveéh out almost immediately by xero-
phytes, since intermediate or mesophytic conditions are seldom seen
where the soil is rock. Furthermore, the xerophytic conditions become
much more extreme on rock bluffs than on clay bluffs. This is well
illustrated at Starved Rock (see fg. 6), where the dominant tree vege-
tation is coniferous, consisting especially of the white pine (Pinus
Strobus) and the arbor vite (Zhuya occidentalis). The herbs and
undershrubs here are also pronouncedly xerophilous, resembling the
vegetation of the sand dunes, e. ¢., Sedaginella rupestris, Campanula
rotundifolia, Pellea atropurpurea, Talinum teretifolium, Opuntia Rafi-

CHICAGO AND VICINITY. 21

nesquit, etc. The entire bluff flora down to the river’s edge is xero-
phytic, except in shaded situations.

When a stream in its meanderings ceases to erode at the base of a
bluff, increased opportunity is given for plant life. Through surface
wash the slopes become more and more gentle. Mesophytic vegeta-

Fic. 7.—Ravine in the Niagara limestone at Lockport, showing the beginnings of a flood
plain.

tion comes in at the foot of the bluff and creeps up as the slopes
decrease. Finally the xerophytes are driven from their last strong-
hold, the top of the slope, and. the mesophytes have come to stay, at
least until the river returns and enters upon another stage of cliff
erosion. The growth of a ravine into a valley with xerophytic bluffs is.
rapid, when expressed in terms of geology, but far less rapid when.
expressed in terms of vegetation. A ravine in the vigor of youth may
develop so slowly that forest trees may grow to a considerable size
without any perceptible change in the erectness of their trunks. Thus,

22 THE PLANT SOCIETIES OF

in figs. 2 and 5 it will be seen that most of the trees stand approxi-
mately vertical. But the activity of the erosive forces, slow as it may
be, is nevertheless revealed by occasional leaning, or even falling, trees.
From the above it is easy to understand that cycles of vegetation often
pass much more rapidly than cycles of erosion, but never more slowly.
During one erosion cycle the mesophytic forest develops at least twice
—once on the ravine slopes, and then finally on the gentler slopes that
betoken approach toward base level.

C. The flood plain.—We may now follow the successive stages in
the development of the flood plain vegetation. While the ravine is
still young, as in fg. 2, there is no permanent stream, but merely tor-
rents, which remain but a short time. As the ravine deepens, widens,
and lengthens, thus approaching the underground water level and
increasing the drainage area, the water remains for a longer and longer
time after each rainfall. As the ravine conditions thus become more
and more hydrophytic, the original flora, perhaps of shade mesophytes
(as Impatiens), becomes replaced by amphibious shade plants, such as
the common buttercup (Ranunculus septentrionalis), Plantago cordata,
various mosses, etc. Together with these forms algz of short vegeta-
tive period may be found in the wet seasons. When the ravine at last
is sufficiently developed to have a permanent stream, a definite hydro-.
phytic flora appears, consisting largely of alge (e. g., Batrachos-
permum), aquatic mosses, and seed plants with finely dissected leaves
and strong holdfast roots (such as Myriophyllum), though these latter
plants are more characteristic of ponds. In the early phases of a
stream the currents are rapid and the vegetation (apart from lower
forms) is sparse, by reason of the difficulty which plants have in secur-
ing and retaining a foothold on the stream bed. This difficulty is due
to the rapid erosion and consequent instability of the substratum, as
well as to the direct destructive aclion of the currents. Fig. 7 shows
one of these young streams whose flora is sparse.

Springs and spring brooks may be classed with ravine streams, but
differ from them in the relative absence of erosion phenomena. This
type of stream is uncommon in the Chicago area, though there are a
few spring brooks near Chesterton. The water supply is much more
constant than in ravine streams, and the shade of the ravines is often
lacking. Besides the aquatics, there may be mentioned a characteristic
brookside flora, including such plants as Symplocarpus fetidus (Skunk
cabbage), Asclepias incarnata (Swamp milkweed), Chelone glabra, Poly-

CHICAGO AND VICINITY. 23

gonum sagittatum, and two or more species each of Eupatorium,
Lobelia, Mentha, Lycopus, and Bidens. The most characteristic
spring brook shrub is the alder (A/mus incana), though the extensive
northern development of alder thickets has no parallel here.

As the energy of the developing stream is checked, the conditions

Fic. 8.—General view of the Illinois valley near Starved Rock, showing islands and anexten-
sive flood plain with trees along the margin. Young islands in the foreground, older islands in
the background.

for plant life become more favorable. In the quiet pond-like waters of
an older stream there may be found many of the aquatics that frequent
the ponds and lakes. In fact, the flora that is given later as character-
istic of half-drained ponds and lakes (such as Calumet lake) may be
transferred almost bodily to sluggish streams, such as the Calumet and
Desplaines rivers.

When streams are old enough, and therefore slow enough, to sup-
port a pond vegetation, they have become essentially depositing rather
than eroding streams, and we find there the development of a flood
plain. While the river is still confined within narrow walls, and may
thus be called young, there may be embryonic patches of flood plain,
representing alternations of erosion and deposition in the stream.
Fig. 7 shows such a condition of affairs; though the stream is young

24 THE PLANT SOCIETIES OF

and more destructive than constructive at that point, there are to be
seen small flood plain areas with their typical tree inhabitants.

There is no place where flood plain development can be better
studied than on growing islands in relatively rapid and yet essentially
depositing streams, such as the Illinois river at Starved Rock. Fig. 8

Fic. 9.—Young island -.n the Illinois river at Starved Rock (close view of island in foreground
of fg. &), seen from above, and showing the destructive action of the river.

gives a general view of the Illinois islands and flood plain. In fgs.
g and zo the lower island (foreground of fg. &) is seen close at hand.
Any obstacle, such as a partially submerged tree trunk, serves to check
the river current and cause a deposition of sand or silt, and before
long a sand bar originates. As in the case of a sand dune, the bar
itself becomes an obstacle to the currents, and hence continually grows
larger.

The first vegetation, as on the lake beach, consists largely of annuals,
especially the giant ragweed (Amdérosia trifida); rushes and sedges,
some annual and some not, are also present, but are less conspicuous.
The perennials that manage to survive one season are largely washed

CHICAGO AND VICINITY. 25

away in the winter and spring, so that in reality the vegetation is almost
exclusively annual. The first woody plants to get a more or less per-
manent foothold: here are willows (Sadix nigra and S. longifolia).
While islands of the above type gain more soil than they lose, a
comparison of figs. 9 and zo shows that the river erodes above and
deposits below. As a consequence, these islands migrate down the
river, as well. as grow in area year by year. Hence the upper part of
the island is the oldest, as the vegetation well shows. igs. 8 and so

Fic. 10.—Same island as shown in fg. 9, but seen from below, and showing the constructive
action of the river. Naked sand bar recently formed at the lower end of the island (left hand).
Ambrosia farther toward the right, willows on the older part of the island (extreme right).

show at the lower end the sand bar, which comes to a point, and is so
young or’so exposed to submergence as to be barren of vegetation.
Next comes the Ambrosia, then the willows, and finally a characteristic
flood plain forest (background of jg. 8). The asymmetry of the
river island vegetation is in striking contrast with the zonal symmetry
of pond islands, as will be shown later (see fg. 79). The cause is
evident, viz., the relative lack of symmetry in river currents as com-
pared with pond currents.

The gradual encroachment of the land upon a stream through con-
tinuous deposition is well shown along the Desplaines river, and toa
less complete degree along the Chicago river and Thorn creek. In
the Desplaines bottoms the sand bar and island formations of the IIli-
nois are largely absent, the currents being much less rapid. In the
shallow water near the margin of the river are various hydrophytes,
such as Sagittaria (Arrowhead), Rumex verticillatus (Swamp dock), etc.

26 THE PLANT SOCIETIES OF

The outermost fringe of land at ordinary low water is often almost as
barren of vegetation as are the islands, but the soil is fine, and hence
makes a mud flat instead of a sand bar. Immediately after the spring
freshets have gone, an alga vegetation is frequently found on these
flats, consisting especially of Botrydium and Vaucheria. Later in the

Fic. 11.—Flood plainof the Des Plaines river at Glendon Park, showing encroachment on
the river. Willows in the foreground, cottonwoods farther back,

season, annuals, or even scattered perennials, may occur here, though
the winter and spring floods uproot or bury most of this vegetation.
The Ambrosia and willow vegetation soon appears, as described above.
The river maple (Acer dasycarpum) usually appears with or soon after
the willows. After the willows the cottonwood (Populus monilifera)
and the ash (fraxinus Americana) soon come in. Fég. 7% shows an
advancing flood plain of this type; willows are seen on the margin
and cottonwoods farther back.

Gradually the growing flood plain becomes dry enough to permit
the germination and development of a true mesophytic flora. The
trees named above, especially the willows, are largely replaced by others
that seem better adapted to the changed conditions; among these are
the elms (U/mus Americana and U. fulva), the basswood (Zilia Amer-

CHICAGO AND VICINITY. 27

cana), the walnut and butternut (/uglans nigra and /. cinerea), the
pig-nut (Carya porcina). In this rich flood plain forest there are many
lianas climbing over the trees, ¢.g., greenbrier (Smilax hispida), grape
(Vitis —various species), Virginia creeper (Ampelopsis quinguefolia),
and poison ivy (Rhus Toxtcodendron).

Fic. 12.—Mesophytic flood plain forest in the bottoms of the Des Plaines river at Riverside.
Elms and basswoods. Rich herbaceous vegetation, consisting largely of Phlox.

The undergrowth in these river woods is very dense and luxuriant,
the alluvial character of the soil making it very fertile. Among the
shrubs are the thorns (various species of Crategus), the gooseberry
(Zibes Cynosbat), and many others. The herbaceous vegetation is
dominantly vernal, the shade being too dense for a typical estival flora.
Prominent among the spring flowering herbs are 77¢/ium recurvatum,
Phlox divaricata, Polemonium reptans, Hydrophyllum Virgintcum
(Waterleaf), Mertensia Virginica (Lungwort), Collinsia verna, Claytonia
Virginica (Spring beauty), Lrythronium albidum (Dogtooth violet),
Arisaema triphylum and A. Dracontium (Indian turnips), WVepera
Glechoma (Ground ivy), Jsopyrum biternatum, Caulophyllum thalic-

28 THE PLANT SOCIET/ES OF

troides (Cohosh), Viola cucullata, Galium Aparine. Other character-
istic herbs are the nettles (Ur#ica gracilis, Laportea Canadensis), various
umbellifers (Heracleum, Cryptotaenia, Sanicula, Osmorrhiza), and the
parasitic dodder (Cuscuta Gronovit). Fig. 12 shows a characteristic
mesophytic flood plain forest along the Desplaines river; underneath

Fic. 18.—Flood plain forest along a smalk stream at Lockport, showing a rather striking
collection of southern trees (see text). Cuffee tree in the foreground.

the elms and basswoods is seen a rich herbaceous flora, consisting
largely of Phlox, which the picture shows in full bloom.

In some of the bottom lands there is a rather striking collection of
trees, whose chief range is mainly southward. 7g. 73 shows a flood
plain tree group near Lockport, most of whose members are largely
southern, viz., the coffee tree (Gymnocladus Canadensis), seen in the
foreground; the pawpaw (Astmina ¢riloba), the sycamore (Platanus
occidentalis), and the hackberry (Celts occidentalis.) In other flood

CHICAGO AND VICINITY. 29

plains there may be found the mulberry (A@orus rubra), the red bud
(Cercis Canadensis), the buckeye (.2ésculus glabra), and the tulip (Zzrzo-
dendron tulipifera).

None of these trees are common in our district, and only Celtis
may be regarded as frequent. These relatively southern trees are
found not only along the Desplaines and its tributaries, where there is
supplied a continuous habitat along the river southward, but also along

Fic. 14.—Flood plain of the Calumet river near Chesterton, showing the beginnings of ter-
race formation, indicated more by the falling elm than by the topography.

the Calumet and its tributary, Thorn creek. The occurrence of the
tulip is full of interest, since it has been found thus far chiefly (perhaps
only) in the vicinity of the dunes. Its occurrence has been noted
especially at Chesterton along a small stream which empties into Lake
Michigan at that point; the tulip has also been found away from
present streams, but apparently in old valleys whose streams have been
diverted by dune activity. The confinement of these southern trees to
flood plains is not strange, since in such habitats are given the most
congenial conditions that can be found in our area.

The vegetation on flood plains is not always as described above.
Sometimes meadows are found instead of forests; this condition is par-
ticularly well shown along Thorn creek. /zg. 78 shows a stretch of
meadow of this type. Besides various grasses, such as Poa pratensts

30 THE PLANT SOCIETIES OF

(Blue grass) and Agrostis alba vulgaris (Red top), there are often other
plants in abundance, e. g., Zhalictrum purpurascens (Meadow rue), Fra-
garia Virginiana (Strawberry), and Anemone Pennsyluanica. The eco-
logical meaning of the meadow is not clear. Probably mowing or
grazing is responsible for the failure of a mesophytic forest to develop.

Fic. 15.—Terrace in the flood plain of the Des Plaines river at Glendon Park, showing how
amesophytic flood plain may become xerophytic. The opposite bank shows deposition and
flood plain enlargement (fg, 77). ;

Extensive thorn (Crategus) thickets sometimes occur in these meadows,
and probably betoken the beginning of a mesophytic forest. Exten-
sive and apparently natural meadows are found in the Calumet valley.

As we have seen, the climax type of vegetation on the flood plain
is the mesophytic forest; but here, as well as on the river bluffs, the
climax may be but temporary. Retrogression is almost sure to come
in connection with terrace formation. While it is true that deposition
is the main feature of flood plains, it is also true that erosion has not
ceased; the downward cutting of the river once more causes vertical
banks, though this time in its own flood plain. This action is seen in
jig. 74, which shows the beginning of the new erosive phase, and its
indication in the falling elm. There has doubtless been lateral erosion
here also, since elms are not usually marginal trees. zg. 75 shows

CHICAGO AND VICINITY. 31

the erosion of the flood plain still farther advanced; this bank is just
opposite the willow vegetation shown in Aig. 77, hence there is depo-
sition on one side and cutting on the other. A river may thus swing
quite across its flood plain, destroying all that it has built, including
the mesophytic forest. Not only is the vegetation destroyed directly,

Fic. 16.—An oxbow lake in the flood plain of Thorn creek. The willows are antecedent,
dating back to a stream margin, while the shrub (Cephalanthus) and herb vegetation is asso-
ciated with the present undrained condition.

as shown in fg. 74, but also indirectly, since the lowering of the river
causes the banks to become more xerophytic. In place of the her-
baceous mesophytes, Equisetum and other relatively xerophytic forms
may appear, though the trees usually live until directly overthrown by
the river.

One more phase of river activity may be brieflysketched. In mean-
dering over a flood plain, serpentine curves, or oxbows, are frequently
formed. In time the river breaks across the peninsula, and the oxbow
remains as a crescentic lake. The conditions radically change almost
immediately, and the river life is replaced by pond life, The change
is even more striking on the margins, where the old plants pass away
and the forms of undrained swamps come in. ig. 76 shows the rem-

32 THE PILANT SOCIETIES OF

nant of one of these oxbows; on the farther side are old and dying
willows, trees that look back to the well-drained river margin. On
either side of the pond are seen clumps of the button bush (Cepha-
lanthus occidentalis), one of the most characteristic plants of undrained
swamps. ‘Thus the willows are antecedent and the button bush subse-

Fic. 17.—A dead oxbow lake in the flood plain of Thorn creek. A willow still remains at
the right, while the shrubs (Cephalanthus) have closed in upon the lake.

quent to the formation of the cut-off. zg. 77 shows a portion of the
same, in which the willows, and even the pond itself, have gone, and
only the marginal button bush is left, though in this case the margin
occupies the center of the origimal pond. Near Starved Rock an
extinct oxbow lake on the flood plain of the Illinois river contains an
extensive patch of Sphagnum and Osmunda, among the most character-
istic plants of undrained swamps. There are many undrained swamps,
some with tamaracks, in the Calumet valley. The future of these
swamps is like that of other swamps, and will be described in the next
section. 7g. 78 shows a morainic island in the Thorn creek flood
plain; the stream has meandered, but has thus far left this detached
fragment of the morainic mainland with a large part of its original
flora.

CHICAGO AND VICINITY. 33

In closing the section on rivers, al] that is needed is to emphasize
again the idea that the life history of a river shows retrogression at
many points, but that the progressions outnumber the retrogressions.
Not only this, but retrogressive phases are relatively ephemeral. Thus
a river system, viewed as a whole, is progressive, and through all its

Fic. 18.—Flood plain of Thorn creek near Glenwood, showing a meadow instead of a forest.
At the center is an uneroded island, detached from the morainic mainland, seen at the left. The
vegetation of the island 1s similar to that of the morainic upland.

vicissitudes there is an ever-increasing area of mesophytic forest.
When the theoretical base level is reached, there seems to be no
‘apparent reason why mesophytic forests should not be developed
throughout most of the great plain.

2. THE POND-SWAMP-PRAIRIE SERIES

A. The pond.—There are all gradations between rapid streams and
completely undrained ponds, and corresponding with these various
‘gradations are characteristic plant species. It will be convenient to
‘subdivide the series under discussion into two parts, the first dealing
with undrained ponds and swamps, the second with half-drained ponds

and swamps.

NN
34 THE PLANT SOCIETIES OF

No two floras can be more unlike in species or in adaptations than
are the typical brookside and swamp floras. Though each type may
be called hydrophytic, so far as the water is concerned, the vegetation
is really hydrophilous in the first case, but pronouncedly xerophilous
in the second. Peat bogs, which may be taken as the type of undrained
swamps, have a remarkable assemblage of xerophytic adaptations, such
as leathery or hairy leaves, and special structures for water absorption.
Schimper believes that these structures are due to the difficult absorp-
tion in peaty soil, the humus acids and the lack of oxygen being detri-
mental to normal root activities. For similar reasons the normal soil
activities of bacteria and fungi are lessened, and as a result of this
relative lack of decay great quantities of peat accumulate. All of
these peculiarities of peat bogs may be referred to the lack of drainage,
since the stagnant conditions prevent oxidation and the removal of
the bumus acids. The lack of drainage is of course due to topographic
conditions. Peat bogs and undrained lakes, therefore, are features of
a young topography, since several agencies combine to cause their
rapid destruction. Rivers may work back and tap the undrained lakes
or inlets may fill them up. Probably the most important agent in the
death of undrained lakes, however, is the vegetation, as will be seen
later. The great abundance of lakes and ponds in the young glaciated
regions as compared with older regions to the south is a striking
proof of their short life.

In the immediate neighborhood of Chicago typical peat bogs are
scarce. They find their best development in the depressions of the
dune region, where they may be called abundant. Wherever a sag
between two dunes is low enough to retain moisture for the greater
part of the season, the conditions favor the development of an un-
drained swamp flora. If the depression is so low that the water level
outcrops throughout the year, fhen there is an undrained pond or
lake. The first flora in this latter case consists of plants that are able
to exist with little or no change in the water of the pond except
through rain and evaporation. Among these plants the alga Chara
takes a prominent place. The water lilies (Nymphaea and Nuphar)
are an exceedingly important constituent of this first vegetation, as is
also Utricularia, which is represented by several species. The above
species, together with others, play a great part in filling up lakes, since
their remains accumulate with almost no decay. Chara in particular
is a soil former of great importance. The rapidity with which these

CHICAGO AND VICINITY. 35

filling processes are carried on is striking; in pools of known age
among the rubbish heaps of Jackson park the author has noticed
accumulations of Chara peat amounting to one or two inches per
year.

B. The undrained swamp.—lIt is obvious that the processes outlined
in the preceding paragraph must eventuate in the death of the lake or
pond involved and its replacement by a marsh, entirely apart from
ordinary erosive activities. Indeed, as has been stated, these activities
are relatively unimportant here; this fact is shown by the absence of
‘ordinary sediments from most peat beds. As the aquatics make the
pond shallower and shallower, they make it more and more unfit for
themselves and fit for their successors, viz., those plants which grow
along pond margins. Among the first plants of this type are various
sedges (Carex), also the bulrush (Scerpus Jacustris), though this latter
species is more characteristic of the half-drained margins than of those
under discussion here. Other marginal plants of our peat bogs are
Menyanthes trifoliata (Buckbean) and Potentilia palustris (Swamp
cinquefoil).

The vegetation that follows may be called tvpical of peat bogs.
The dominant plants are usually shrubs, especially the leather leaf
(Cassandra calyculata); this plant may be so abundant as to give tone
to the landscape. /%g. 79 shows some Cassandra islands in a sedge
swamp. It is clear that the islands represent places where in the
original lake the water was shallow. The present remnant of the lake
is shown at the left. Not only have the sedge zones advanced upon it
from all sides, but centers of sedge growth appear also in shallow
places in the lake itself. Just as the sedge zone encroaches upon the
lake, when conditions become favorable, so the Cassandra zone
advances on the sedges. Again, a tree zone advances on the shrubs,
as will be seen farther on. The zonal arrangement of plant societies
that has just been seen is a feature of most peat bogs, and is due to
the symmetry of lake and bog conditions. It will be observed that
along the lake margin the zones advance toward a common center,
while on the islands the advance is from a center. Eventually, of
course, the marginal and island zones will merge.

Besides Cassandra many other plants are commonly found in the
shrub zone. Other shrubs are the swamp blueberry (Vaccinium corym-
bosum), the cranberry (Vaccinium macrocarpon), the dwarf birch (Betula
pumila), the alder (A/nus incana), the hoary willow (Salix candida),

36 THE PLANT SOCIETIES OF

and the poison sumach (RAus venenata). Characteristic herbs,
especially in the open places, are the pitcher plant (Sarracenia pur-
purea), the sundew (Drosera rotundifolia), various orchids, as Calopogon
pulchellus, Pogonia, and Cypripedium; sedges, as Eriophorum and
Dulichium ; Woodwardia Virginica, and Elodes campanulata. One of
the most typical plants of these places is the peat moss, Sphagnum.

Fic 19.—Typical peat bog in a depression between established dunes at Miller.. Relict of
the original pond at the left. Sedges (light-colored vegetation) are encroaching on the lake,
while shrubs, mainly Cassandra, are encroaching on the sedges. Cassandra islands toward the
right. Advance of conifers on Cassandra (seen in its beginnings on the islands) shown at the
extreme right.

The flora just mentioned has many interesting features which are
well known and may be passed over briefly. The highly xerophytic
character of this plant society has already been noticed, and the rea-
sons for it briefly given. The xerophytic structures are well illustrated
in the leathery leaves of Cassandra and the absorption and storage
adaptations of Sphagnum. Many bogs of this type are very spongy
and unstable, whence the name quaking bogs; this feature is due to
the rapid growth of the vegetation and the absence of ordinary inor-
ganic soils for a considerable depth. The similarity of the peat bog
vegetation throughout the northern hemisphere is one of its most
striking features. Not only the adaptations but the species themselves

CHICAGO AND VICINITY. é 37

are similar over vast areas; the conditions are unique and the flora also.
None of our plant societies, not even the lakeward dune slopes, have
such a pronounced northern flora as do the peat bogs. No contrast
could be more striking than that between the southern vegetation of
the flood plains and the northern flora of the bogs.

fig. 79 shows that a coniferous vegetation, now represented by

Fic.,20.—Tamarack swamp in an undrained portion of the Calumet flood plain at Miller.
Peat bog herbs and shrubs in the foreground.

but two or three small trees at the centers of the islands, is to follow
the Cassandra. Such an advance of conifers on Cassandra is shown in
the background at the right. The most typical conifer in such cases
is the tamarack (Larix Americana); with this the arbor vitae (Thuya
occidentalis) is sometimes found. Larix and Thuya swamps reach but
an imperfect development in our region, and little need be said about
them. The shade in these forest swamps is so dense that bare patches
of soil are often seen. The vegetation consists largely of shade plants,
among which may be mentioned Mnium and other similar mosses,
Coptis trifolia (Goldthread), Cornus Canadensis, Viola blanda (White
violet), and Impatiens. The tamaracks appear to be succeeded by the
pines (Pinus Strobus or P. Banksiana), and they in turn by oaks, as
the soil becomes drier and better drained, and thus more adapted

38 THE PLANT SOCIETIES OF

to deciduous trees. ig. 20 shows a tamarack swamp near Miller, °
Ind.

Not all peat bogs havea history like the above. Just as some flood
plains are forested and others not, so some peat bogs grow up to
shrubs and trees, while others are dominated, for a long time at least,

Fic. 21.—Shallow, undrained swamp (peat bog) at Dune Park. In the foreground the
relict of the original pond, with water lilies, then in order, encroaching zones of bulrushes.
sedges, willows, and pines. The oaks in the batkground are onan established dune, and are
not encroaching on the swampy soil.

by herbs and grasses. ig. 27 shows a swamp of this character. Bul-
rushes are seen to be encroaching upon the water lily vegetation, while
back of the bulrushes, instead of Cassandra, is a zone with sedges and
grasses and scattered willows. Among the species other than sedges
and grasses in a plant society like this are Vola sagittata and V. lan-
ceolata, Potentilla Anserina, Fragaria Virginiana (Strawberry), Par-
nassia Caroliniana, Sabbatia angularts, Gentiana crinita, Gerardia pur-
durea, Castilleta coccinea (Painted cup), Aletris farinosa, Iris versicolor,

CHICAGO AND VICINITY. 39

Sisyrinchium angustifolium (Blue-eyed grass), Hypoxys erecta (Yellow-
eyed grass), Xyris flexuosa, Triglochin maritima. The shrubs in such
places are chiefly Sa/ix glaucophylla (Glaucous willow), Cornus stolo-
nifera (Osier dogwood), Potentilla fruticosa (Shrubby cinquefoil), Hyper-
tcum Kalmianum. The conditions that determine this type of bog, as
contrasted with the Cassandra type, are not clear. The soil is hard,
compact, shallow, and usually sandy; it may be that this type develops
in shallow depressions, while the. type with spongy, quaking ground
develops in deeper depressions. This second type much more closely
resembles the half-drained swamps in its flora than does the Cassandra
type, although so far as drainage is concerned it agrees with the Cas-
sandra bogs.

There is yet a third type of swamp which still more closely resem-
bles the half-drained swamp inits flora. It is found along the edge of
the Calumet valley near Dune Park, also at West Pullman. In this
case the soil is rather deep and rich, in which respects there is agree-
ment with the first type rather than the second. Grasses and sedges,
but of a more luxuriant type, dominate here also, and with them are
found such plants as Cephalanthus occidentalis (Button bush), Aspidium
Thelypteris, Onoclea sensibilis (Sensitive fern), Saxifraga Pennsylvanica,
Caltha palustris (Marsh marigold), Viola blanda, Polygala sanguinea.
Sphagnum occasionally occurs here, as it never does in the second
type. .Here again there is doubt as-to the determining conditions, but
it may be that things can be explained by the difference in the drain-
age. The ultimate fate of the second and third swamp types is not
known. The relative absence of trees and shrubs is certainly natural
and in no wise due to man. Possibly local prairies will be the final
type, or it may be that the forest will come in. ig. 27, which shows
pines encroaching upon the grassy areas, favors the latter view. So do
some of the facts seen in the Calumet valley.

All of the peat bog types have a characteristic marginal flora, z. ¢.,
the vegetation at the margin of the original lake is essentially alike in
all cases. These plants, as well as those of Cassandra bogs, are the
same over wide areas. The most common members of the bog margin
flora are the sour gum (WVyssa sylvatica,) the aspen (Populus tremuloi-
des), Ilex verticillata, Pyrus arbutifolia (including var. melanocarpa),
Spiraca salicifolia and S. tomentosa, Rubus hispidus, Gaultheria procum-
bens (Wintergreen), Osmunda cinnamomea, O. Claytoniana, O. regalis,
Betua papyrifera (Paper birch), and Polytrichum commune. This vege-

40 THE PLANT SOCIETIES OF

tation originates outside the swamp, and may be regarded as xerophytic;
however, it often encroaches upon the swamp as the latter develops.
At Thornton there is a dead swamp which is now almost entirely occu-
pied by this xerophytic bog margin flora, only a few of the original
swamp plants now remaining. Near Morgan Park isa bog margin flora
without a bog; a shallow trench has been dug and in this trench there
have appeared various peat bog plants, ¢. g., Sphagnum. These con-

Fic, 22.—Encroachment of bulrushes on Calumet lake, showing how plants may destroy
lakes.

siderations show that bog margin floras, though associated with most
bogs, are not necessarily genetically connected with them.

A word may be said about undrained swamps among the active
dunes. The conditions here, of course, are far more severe than in ordi-
nary peat bogs and only a few spedies are able to endure in such a hab-
itat. The most typical herb is Juncus Balticus littoralis. Seedlings of
the cottonwood, as well as the long-leaved and glaucous willows, ger-
minate in these wet depressions. Reference will be made to these plants
in connection with the dunes.

In the morainic portions of our territory there are few if any peat
bogs as described above, although they are usually more typical of
moraines than of other topographic areas. On account of the clay soil
which characterizes the morainic uplands there are many patches of
swampy woods throughout the district. Shallow depressions of this

CHICAGO AND VICINITY. Al

type in sandy soil would not have a swamp developed. Morainic for-
est swamps are characterized by several trees, viz.: the bur oak, swamp
white oak, and scarlet oak (Quercus macrocarpa, Q. bicolor, and Q. coc-
cinea), the red maple.(Acer rubrum), the elm (Ulmus Americana), and
the ash (Fraxinus Americana). Other species are Cephalanthus occiden-
Yalis (Buttorr bush), Salix atscolor, Ribes floridum (Wild currant), Carda-
mine rhomboidea purpurea (Spring cress), Ranunculus septentrionalis

Fic. 28.—Pond at Waukegan almost destroyed by bulrushes.

(Buttercup). This vegetation is ultimately supplanted by the mesophytic
forest. A vegetation allied with that of swamps is the amphibious ditch
flora with such plants as Vasturtium palustre (Ditch cress), Penthorum se-
doides (Ditch stonecrop), Proserpinaca palustris (Mermaid weed), Zud-
wigia palustris, Polygonum Hydropiper (Water pepper), etc.

Calumet lake and Grand Calumet river may be taken as types of
half-drained waters. We have here conditions that are midway between
those of peat bogs and those of ordinary rivers. The vegetation is sub-
ject neither to the currents of the rivers nor to the stagnant conditions
of the peaty lakes, and hence the luxuriance of the flora is far greater
than in either of the other instances. The aquatic vegetation is rich
both in species and individuals. Here is to be found a great wealth of
alga vegetation, including such forms as Cladophora, Spirogyra, Oedo-
gonium, Hydrodictyon. Among the floating plants are Riccia, Riccio-
carpus, the duckweeds (Spirodela, Lemna, and Wolffia). There are also
a large number of attached plants, including many species of Potamo-

42 THE PLANT SOCIETIES OF

geton (Pondweed), Ranunculus aquatilis (White buttercup), Brasenia, Ne-
lumbo (Lotus), Myriophyllum (Water milfoil), Ceratophyllum (Horn-
wort), Elodea (Waterweed), Vallisneria (Tape grass), and Naias. Thisrank
growth of vegetation fills the lake up rapidly, since the currents are not
sufficient to carty off the plant remains. There is a rapid advance of
marginal plants upon the lake, a phenomenon that is shown in jig. 22,

Fic. 24.—Typical grass prairie near Pullman. This prairie has been reclaimed naturally
from Lake Calumet, and has passed through bulrush and sedge stages.

where the scattered bulrushes (Scirpus /acustris) are seen to be soon fol-
lowed by a dense bulrush society. With or soon after the bulrushes
are a number of marginal plants, @specially Zypha /atifolia (Cattail),
Pontederia cordata (Pickerel weed), Sparganium curycarpum, Sagittarta
variabilis and S. heterophylla (Arrowheads), Zizania aquatica (Wild rice),
Phragmites communis (Reed), Acorus Calamus (Sweet flag), and Erio-
phorum cyperinum. Fig. 23 shows a stage in which a lake has been ali
but destroyed by a rank bulrush vegetation.

C. The prairte—Sedges encroach rapidly upon the bulrushes as the
new soil becomes raised more and more above the lake, and grasses in
‘turn encroach upon the sedges, forming a prairie. zg. 2g shows an
expanse of grassy prairie which has developed through these successive

CHICAGO AND VICINITY. 43

stages from Calumet lake. Skokie marsh and Hog marsh are undergo-
ing transformations of this character also. Sometimes with the prairie
grasses are a number of coarse xerophytic herbs, largely composites, as
Silphium laciniatum (Compass plant), S. cerebinthinaceum (Prairie dock),
S. integrifolium (Rosin weed), Lepachys, Solidago rigida, Aster, Liatris
(Blazing star), with some legumes, as Amorpha canescens (Lead plant),

Fic. 25.—Prairie at Pullman in which the compass plant (Silphium) grows with the grasses.
This prairie is much older and drier than that shown in /rg. 2¢

Petalostemon (Prairie clover), Melilotus (Sweet clover), and Baptisia,
Eryngium, Dodecatheon (Shooting star), Phlox, Adium cernuum (Wild
onion). A Silphium (Compass plant) prairie is shown in fg. 25. The
prairies of our area are in the basin of the glacial Lake Chicago, and
hence all may be referred to a lake or swamp origin, exactly as prairies
are developing from Calumet lake today. This explanation of the prairie,
an undoubted explanation for the cases in hand, must not be applied to
the great climatic prairies farther west. Whether the Chicago prairies
will ever become forested is a question not easily answered. There
are signs of it in some places, as at Stony Island, but this topic needs
more detailed treatment than can be given here.

The processes outlined in‘this section are rapid. The mesophytic
prairie or forest develops from the lake or marsh, while the region as a
whole still retains a young topography. Thus this mesophytic assem-

44 THE PLANT SOCIETIES OF

blage, like that of the ravine slope, is bound to pass away, though its
life tenure is much longer. Sooner or later river action will enter;
there will be developed ravines, xerophytic bluffs, and ultimately flood
plains, again with a mesophytic flora. A broad survey then shows a
rapid development to a somewhat prolonged temporary climax, and
finally, after ravine and bluff vicissitudes, there appears the true and
more enduring climax of the mesophytic flood plain.

3. THE UPLAND SERIES.

A. The rock htl,—While all of a land area is eventually worked
over by stream activities, and can thus be referred to the river series,
other activities are at work in a young topography. The swamp
series which has just been discussed is one illustration. So also there
are hills which are not due to erosive processes, but to other causes,
notably, in our region, morainic hills and sand hills. There are rock
hills, also, which are not connected with the present erosion cycle. All
of these hill types have their peculiar vegetation features, and must be
discussed apart from river activities, since they have an interesting his-
tory before they are attacked by stream erosion.

We may speak first of rock hills, which in the vicinity of Chicago
are quite rare, and consist entirely of dolomitic Niagara (Silurian)
limestone. Not only are hills of this limestone quite rare, but surface
outcrops of any kind are uncommon, because of the heavy drift.
Hence the rock vegetation of the Chicago area is not very important.
Perhaps the most interesting outcrop is at Stony Island, where it is quite
easy to trace the various stages in the development of the vegetation.
This rock, like most limestone, is subject to chemical as well as mechan-
ical erosion, but is much more resistant than most limestones, on
account of its strongly dolomitic @haracter. The first vegetation that
gets a foothold is composed of lichens, but the lichen flora appears to
be rather sparse, perhaps because of the chemical nature of the rock,
since lichens are commonly supposed to shun calcareous soils. The
relative poverty of lichens may be due, however, to the easy solution
of the surface rock layers and the consequent difficulty in retaining a
foothold. The limestone is considerably jointed and fractured, and
there is in consequence a rich crevice vegetation, composed of several
mosses, especially Ceratodon and Bryum, and also various grasses.
fig. 26 shows a vegetation of this nature, and among the other crevice

CHICAGO AND VICINITY. 45

plants is an abundance of Sodidago nemoralis. Other species growing
in the crevices or on the first soil which is formed on the rock face are
Potentilla arguta, Verbascum Thapsus (Mullein), Heuchera hispida (Alum
root), Poa compressa (Wire grass), etc. At Thornton there is a rock

Fic. 26.—Slope of limestone ledge at Stony Island, showing mosses and higher plants
establishing themselves in the crevices.

outcrop which gradually recedes from the surface, and it is possible to
tell by the vegetation where the rock surface dips considerably under
the surface of the soil. Where the soil is shallow the dominant plant
is Poa compressa, but as the soil layer deepens it becomes gradually
replaced by oa pratensis (Blue grass). Similarly, at Stony -Island,
crevices can be distinguished in a covered horizontal rock surface by a
sudden change from the xerophytic plants of the shallow soil, that hides.

46 THE PLANT SOCIETIES OF

most of the rock, to the mesophytic plants of the deeper soil which lies
over the crevices. ;

Through rock decay and the accumulation of organic matter a con-
siderable soil comes to be developed where there was at first an outcrop
of bare rock. The opportunity for a shrubby vegetation eventually

Fic. 27.—Limestone ledge at Stony Island, showing vegetation farther advanced than in
%ig. 26. The crevice shrubs here are chokecherries (Prunus Virgintana),

arrives, especially in the crevices. ig. 27 shows such a vegetation
getting a foothold. Among the shrubs in such places are the choke-
cherry (Prunus Virginiana), ninebark (Physocarpus opulifolius), poison
ivy (Rhus Toxicodendron), Rosa humilis, samach (Rhus typhina), hop
tree (Prelea trifoliata), wild crab (Pyrus coronaria). Still later the way
is open for a tree vegetation, at first xerophytic, but ultimately meso-
phytic, as the author has frequently observed in the Alleghanies. There
can be no doubt but that a temporary mesophytic climax can be

‘CHICAGO AND VICINITY. 47

reached even on rock hills, though the probability of this is much
greater where the hill is composed of limestone than in the case of
sandstone or granite.

B. The clay hil Morainic hills are common in the Chicago re-
gion,and almost without exception they are covered with a mesophytic
forest, in which the dominant trees are usually the white oak (Quercus

Fic. 28.—Typical upland clay (morainic) forest at Beverly Hills. The dominant trees here
are red oaks (Quercus rubra), though a white oak (Q. a/éa) 1s shown at the extreme right.

alba), the red oak (Quercus rubra), and the shell-bark hickory (Carya
alba). This is easily the dominant forest type of the Chicago region,
and is remarkably characteristic of morainic areas. The soil in all
cases is a glacial clay or till, heterogeneous in composition, but rich in
food salts. Of all our plant society life histories these are about the
most difficult to unravel, and it is due to the favorable conditions un-
der which they have developed. After the continental glacier left this
region for the last time, it was doubtless on these low morainic hills
that the first mesophytic forests were developed. And they have been
developed for so long that almost no traces of their history are

48 THE PLANT SOCIETIES OF

left behind; we have only the completed product, the mesophytic
forest.

Where these mesophytic forests are disturbed we may perhaps get
some notion of what took place in the first postglacial centuries. On
the clay banks along the drainage canal, and also on recent river bluffs,
one may follow in rapid succession a series of plant societies leading
to the forest. There is here no pronounced lichen or moss stage as on
rock hills, but the first vegetation consists of xerophytic annuals and
perennial herbs. Xerophytic shrubs, especially Salix and Populus,
soon appear. It is not long before there is an extensive thicket forma-
tion with an herbaceous undergrowth. Humus accumulates with great
rapidity, and we soon have almost a mesophytic vegetation in which
the dominant thicket species are likely to be the aspen (Populus tremu-
loides), wild crab (Pyrus coronaria), red haw (Crategus punctata, C.
coccinea, etc.). Such a thicket is the immediate forerunner of the oak-
hickory type of mesophytic forest. When a forest of oak and hickory.
is cut down or destroyed by fire, it returns after a comparatively short
interval, but the first stages in the clearing are thicket stages much
like those just described. Of course it takes much longer to develop
a forest from naked clay soil than from a forest land that has been
cleared. Whether the stages that led up to the first postglacial forests
are such as have been described is very doubtful. It is much more
likely that the first forests were of slow growth and were coniferous in
character, such as are found farther north. zg. 28 shows a typical
morainic hill forest of the above type. Here the dominant tree is the
red oak; a white oak is seen at the right.

Among the shrubs of these morainic forests there may be men-
tioned, apart from the crabs and haws, the hazel (Corylus Americana),
and various species of Viburnum. Many herbaceous plants are found,
among which are Podophyllum (May*apple), Claytonia (Spring beauty),
various species of Aster, Trillium, Geranium maculatum, Viola pubes-
cens (Yellow violet), Anemone nemorosa, etc. Sometimes the bur oak
(Quercus macrocarpa) is the dominant tree in these morainic forests,
though in such cases the habitat is usually more moist or else the
drainage is less perfect. A bur oak forest is shown in fig. 29. The
transition from this type to the morainic swamp forests, already men-
tioned, is an easy one, and bur oaks are often found with the swamp
white oak and other species characteristic of such places.

In spite of the abundance of the type of morainic forest described

CHICAGO AND VICINITY. 49

above, it is scarcely probable that it is anything more than a very
slowly passing forest stage. The fact that in all directions from Chi-
cago the ultimate forest type on morainic uplands is not the oak-
hickory but the maple-beech forest leads us to expect that here. This
latter type seems to be of a higher order in all respects. It is found
in richer soil, where the humus content is very great. Seedlings of the

Fic. 29.—Typical forest of low morainic clay soil, made up chiefly of bur oaks (Quercus
macrocarpa).

beech or maple can easily grow in the relatively light oak forest,
whereas oaks cannot grow in the denser shade of the maple or beech.
Furthermore, oak forests have been seen with a pronounced under-
growth of beech. It would seem that one of the chief factors in
determining the order of succession of forests is the light need of the
various tree species, the members of the cuiminating forest type being
those whose seedlings can grow in the densest forest shade. There
are evidences that the oak forests about Chicago are being succeeded
by the beech or inaple. The best instance of this which the author
has seen is on the low moraines along the Desplaines river west of
Deerfield. The sugar maple (Acer saccharinum) has already been
mentioned as a character plant of the temporary mesophytic forests of
ravines. Here we see it in the more permanent forest of the morainic

50 THE PLANT SOCIETIES OF

hills. The beech (Fagus ferruginea) is much rarer than the sugar
maple, though it is a rather important constituent of the mesophytic
forests about Chesterton. Why the beech-maple forest has lagged so
far behind in the region about Chicago is a question not yet settled.
If these forests elsewhere have had an oak stage it indicates that the
development here is very slow.

Though the forests just described, whether of the oak-hickory or
the maple-beech type, are of a high degree of permanence, it can be
seen that this permanence is but relative. Sooner or later stream
action will enter these districts and base leveling processes will begin
on amore rapid scale. But for these activities the lowering of hills
would be very slow indeed, so slow as hardly to interfere at any point
with a luxuriant development of the vegetation. The destruction of
these morainic forests by stream erosion is well shown near the shore
north of Evanston, and also along Thorn creek. fig. 78 shows a
morainic island in a flood plain, the sole remnant of an extensive
stretch of upland mesophytic forest. We must therefore regard upland
forests as temporary also, though they endure for a much longer time
than do the temporary mesophytic forests of the ravines.

C. The sand hill—A third type of upland is found in the sand
hills, but since most of these in our district are of dune origin, their
treatment will be deferred until later.

B. THE COASTAL GROUP.
1. THE LAKE BLUFF SERIES.

The plant societies that have been discussed hitherto may be found
in many if not in most inland districts. The societies that follow, on
the other hand, are best worked out only in connection with the coasts
of oceans or great lakes. Thedretically a bluff may be composed of
any kind of rock or soil, but those of our area are composed of mo-
rainic clays, and the life histories that follow will not hold good in
other conditions. It may be noted here that there is a short stretch
of rocky shore with lithophytic alge at Cheltenham, but there is
nothing that in any way approaches a rock cliff.

Wherever a sea or lake erodes rather than deposits, there is com-
monly developed a sea cliff of greater or less dimensions. The mate-
rial which is thus gathered may be deposited elsewhere in the form of
beaches, and later the wind may take up the sands from the beach and

CHICAGO AND VICINITY. 5}

form dunes. The Chicago area gives splendid examples of these two
types of sea activity; to the north of the city is an eroding coast line
with its bluffs, and to the south and southeast is a depositing coast
with extensive areas of beach and dune.

The lake bluffs at Glencoe give an excellent opportunity for the
study. of the life history of a sea-clitf vegetation. There can. be al-
most no other habitat in our climate which imposes such severe condi-
tions upon vegetation as an eroding clay bluff. The only possible
rival in this regard is a shifting dune, and even here the dune possesses
some points of advantage so far as the establishment of vegetation is
concerned. In the first place, the conditions as to exposure are
almost identical with those of a dune; the heat of midday and of
summer and the cold of night and winter are extremely pronounced;
the intensity of the light and the exposure to wind make the condi-
tions still more severe. In other words, the only plants that can grow
on these lake bluffs, at least in the earlier stages, are pronounced
xerophytes. Again, the character of the soil is unfavorable, for while
the clay is wet in the autumn, winter, and spring, it dries out ‘in the
summer and becomes almost as hard as rock. In the heat of summer:
the conditions for vegetation are no better on the hard, dry slopes of a
clay bluff than on the hot, dry sands of a dune. Finally, as to insta-
bility: it is doubtless the constant shifting of the sand which in the
last analysis accounts for most of the poverty of the dune vegetation.
It is similar on clay bluffs, for when the waves undermine the cliff at
its base, the action of gravity causes great masses of material to fall
down from the entire cliff face. Furthermore, when the clay is satu-
rated with water, great portions of the cliff face slide down, entirely
apart from the action of the sea or lake. At no time, then, is an
eroding bluff any more stable than a naked dune.

It becomes evident from a survey of the bluff conditions that all
vegetation is impossible so long as active erosion by the lake con-
tinues. Not only this, but vegetation at the top of the bluff is soon
destroyed. fig. 30 shows a naked cliff of this character ; at the top
there can be seen overhanging turf, giving evidence both of the
destructive action of the lake and also of the tenacity with which a
grass mat holds its place in the presence of adverse conditions. Near
the center of fg. 37 may be seen a white oak which was almost over-
thrown by the erosive activities, but which has been preserved through
the cessation of erosion at this point. The gully shown near the cen-

52 THE PLANT SOCIETIES OF

ter of fig. 70 is seen in closer view in fig. 7, the absence of vegeta-
tion, save that which has slid down from above, is very striking.

If for any reason the lake activities at the base of the cliff are
stopped, an opportunity is offered for the development of vegetation.
At Glencoe the cliff erosion has been checked to some extent by arti-
ficial means, and one can see various phases of cliff life within a small

Fic. 30.—Sea cliff along the eroding shore at Glencoe, exposing the morainic clay. Vege-
tation almost entirely absent. Projecting turf mats at the top show the tenacity with which
the vegetation holds its ground in the face of the erosive forces.

area. When the erosion at the base of the bluff ceases, conditions be-
come much more stable, though landslide action may still occur. In
time the slope gradient becomes so low that the cliff soil is essentially
stable; when this time arises vegetation develops with great rapidity
in spite of the xerophytic conditions, which are still as pronounced as
before. It is very obvious, therefore, that it is the instability of the
eroding cliff and not its xerophytic character which accounts for the
absence of plant life.

The first vegetation is commonly made up of xerophytic herbs,
both annual and perennial. Among these are the sweet clover (Meli-
lotus alba), various annual weeds, various species of Aster, especially

CHICAGO AND VICINITY. 53

A. laevis, Equtsetum hyemale (Scouring rush), various grasses, etc.
Soon there develops a xerophytic thicket vegetation, such as is shown
in fg. 37. This may be called the shrub stage of the captured cliff, and
among the dominant species are the juniper and cedar (Juniperus
communis and J. Virginiana), Salix glaucophylla (Glaucous willow), the

Fic. 31.—Sea cliff at Glencoe, at a place where lake erosion has ceased. Shrubs (largely
‘cedars and willows) prominent as well as herbs. Absence of lake erosion also indicated by the
gentle slope, as compared with jig.3o. The leaning oak at the top bears witness to former
erosive forces.

osier dogwood (Cornus stolonifera), Shepherdia Canadensis, various
sumachs (Rhus typhina and R. glabra). The following tree stage is
dominated by various poplars (Populus tremuloides, P. grandidentata,
P. monilifera), the hop hornbeam (Os¢rya Virginica), the white pine
(Pinus Strobus), the red cedar (Juniperus Virginiana), and some of the
oaks (probably Quercus rubra and Q. coccinea tinctorta). Fig. 32
shows a tree-clad cliff in which most of the above trees are to be
found.

Whether a mesophytic forest would develop on a lake bluff is

54 THE PLANT SOCIETIES OF

something of a question. It seems likely that semi-xerophytic trees
will dominate there for a long time to come on account of the xero-
phytic atmospheric conditions. Particularly at the top of the bluff do
the conditions remain severe, by reason of the great exposure, and also
the dryness of the soil. If the lake should recede for some distance,

Fic. 32.—Sea cliff at Glencoe, where lake efosion has been absent for a long period. Xero-
phytic trees and shrubs, especially conifers, dominate, ¢. g., white pine, red cedar, juniper.

a mesophytic forest could certainly develop on the bluff before it is
reduced to anything like the common level. This is shown on the
ancient lake bluff at Beverly Hills. Here there is an old cliff about
forty feet above the country level, representing a lake bluff of the
Glenwood stage of Lake Chicago.- This bluff has long had a meso-
phytic forest on its slopes, and yet it will be many centuries before
the erosive forces remove all traces of this ancient sea cliff. A still
more striking case is to be seen north of Waukegan, where an ancient

CHICAGO AND VICINITY. 55

lake bluff, higher than that at Beverly Hills and only a mile back of
the present lake shore, is tenanted by a high grade type of mesophytic
forest.

It will be instructive to make a few comparisons between lake bluffs
and other plant societies. Closest to the lake bluff in a physiographic
sense is the river bluff. When a stream has banks of clay, the con-
ditions seem decidedly similar, and yet the flora is not the same. A
comparison of the lake bluffs at Glencoe with the bluffs along Thorn
creek shows that some species are common, notoriously Ostrya, Rhus,
Quercus, Populus. Yet the differences are still more striking, for the
bluffs along Thorn creek do not show Salix glaucophylla nor Shep-
herdia; most striking of all, however, is the entire absence of conifers.
When we compare the lake bluffs with the rock bluffs of the Illinois
river, we find that the resemblances are greater than the differences,
since the river bluffs have conifers, though even here some of the lake
bluff forms are absent. When, however, we compare the Glencoe
bluffs with the dunes, we find that all of the dominant shrubs and trees
of the bluff are found also on the dunes; not only this—the dominant
bluff forms are dominant on the dunes also.

The facts of the preceding paragraph are pregnant with signifi-
cance. One obvious corollary is that, given similar soils but dissimilar
conditions of atmospheric exposure, as at Glencoe and Thorn creek,
the vegetation is unlike. Another and more striking corollary is that,
given the most dissimilar soils possible, viz., the Glencoe clay and the
dune sand, we still have similar vegetation, because the atmospheric
conditions are the same in the two cases. The evidence of the Illinois
river bluffs is less clear; they are more xerophytic than the bluffs along
Thorn creek; but whether this is chiefly due to rock as against clay, or
to greater exposure, is not certain. At all events, these facts show that
it is not enough to know about chemical or physical conditions in the
soil. We cannot divide plants into those of clay, rock, and sand, but
must take into account that most plants have a wide range of life, so
far as soil is concerned, provided the atmospheric conditions are con-
genial. The chief exception to this statement seems to be found, not
in the original soils, but in the superimposed humus. There are many
plants that require humus for their occurrence in nature, but it makes
no difference whether the subsoil is rock, sand or clay, provided alone
that the humus is present in sufficient quantity. It is by reason of this
last fact that the mesophytic forest can appear in all conditions in this

56 THE PLANT SOCIETIES OF

climate, since the mesophytic forest is associated to a high degree with
humus.

2. THE BEACH-DUNE-SANDHILL SERIES. .

A. Zhe beach.—The author has previously discussed in consider-
able detail the dynamics of the dune societies, ‘and it will not be neces-
sary to do more here than to summarize the chief conclusions, and add

Fic. 383.—Beach at Dune Park, showing the smooth and naked lower beach, the middle
beach with its line of débris, the upper beach with scattered shrubs, and the dunes.

a few new data. Before long it is expected that a paper will appear
giving the changes that have taken place since the first observations
were made in 1896. .

The beach in the Chicago area is xerophytic throughout. There is
nothing analogous to the salt marshes of the Atlantic coast, nor to the
hydrophytic shores farther north along Lake Michigan. The lower
portion of the beach is exposed to alternate washing by the waves and
desiccation in the sun, and is devoid of life. ‘The middle beach, which
is washed by winter waves, though not by those of summer, has in con-
sequence a vegetation of xerophytic annuals, the most prominent of
which is Cakile Americana (Sea rocket). The upper beach is beyond

1 Cowes, H.C.: The ecological relations of the vegetation on the sand dunes of Lake
Michigan. Bor. GAz. 27: 95-117, 167-202, 281-308, 361-491. 1849. Also reprinted separately.

CHICAGO AND VICINITY. 57

present wave action, and is tenanted by biennials and perennials in
addition tothe annuals. Ag. 33 shows a beach of this type, the lower
beach being smooth and even, the middle beach covered with débris,
while the upper beach has a scattered perennial vegetation.

The beach at the base of cliffs shows similar subdivisions, though
the zones are much narrower asarule. ‘lhe vegetation, too, is much
the same, though some forms, as Strophostyles, have not been seen as
yet on the beaches of the dune district. At the foot of cliffs there often
occur alluvial fans of sand, which have been deposited by the torrents
during and following rain storms. These fans have a comparatively
tich vegetation, and species sometimes occur here that are not found
elsewhere on the beach.

B. The embryonic or stationary beach dunes.—Wherever plants occur
on a beach that is swept by sand-laden winds, deposition of sand must
take place, since the plants offer obstacles to the progress of the wind.
If these plants are extreme xerophytes and are able to endure covering or
uncovering without injury, they may cause the formation of beach dunes.
Ainong the dune-forming plants of this type are dmmophila arundinacea
(Sand reed), Salix glaucophylla and S. adenophylla (Glaucous and glan-
dular willows), Prunus pumila (Sand cherry), and Populus monilifera
(Cottonwood). The shapes of these beach dunes vary with the charac-
teristics of these dune-forming plants. Ammophila dunes are exten-
sive hut low, because of strong horizontal rhizome propagation. Prunus
and Populus dunes are smaller but higher, because of the relative lack
of horizontal propagation and the presence of great vertical growth
capacity. Dunes are formed more slowly in protected places, and here
the dune-forming species may be plants that are ill adapted to the
severest beach conditions, such as the creeping juniper. A beach dune
of the type just described is shown in fig. 34.

C. The active er wandering dunes. The dune complex.—The sta-
tionary embryonic dunes on the beach begin to wander as soon as the
conditions become too severe for the dune-forming plants. The first
result of this change 1s seen in the reshaping of the dune to correspond
with the contour of a purely wind-made form. The rapidity of this
process is largely determined by the success or failure of the dune-
formers as dune-holders. The best dune-holders are Calamagrostis,
Ammophila, and Prunus.

‘There are all gradations between a simple moving dune and a mov-
ing landscape; the latter may be called a dune-complex. ‘The complex

THE PLANT SOCIETIES OF

58

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59

CHICAGO AND VICINITY.

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60 THE PLANT SOCIETIES OF

is a restless maze, advancing as a whole in one direction, but with indi-
vidual portions advancing in all directions. Itshows all stages of dune
development and is forever changing. The windward slopes are gentle
and are furrowed by the wind, as it sweeps along; the lee slopes are
much steeper. The only plant that flourishes everywhere on the com-
plex is the succulent annual, Corispermum hyssopifolinm (Bugseed),
although Populus monilifera (Cottonwood) is frequent. The scanty flora
is not due to the lack of water in the soil, but to the instability of the
soil and to the xerophytic air.

The influence of an encroaching dune upon a pre-existing flora
varies with the rate of advance, the height of the dune above the coun-
try on which it encroaches, and the nature of the vegetation. The burial
of forests isa common phenomenon. The dominant forest trees in
the path of advancing dunes are Pinus Banksiana (Scrub pine) and
Quercus coccinea tinctorta (Black oak). These trees are destroyed long
before they are completely buried. The dead trees may be uncovered
later, as the dune passes on beyond. A pine forest upon which a dune
is encroaching is shown in fg. 75, while such a forest after the dune
has passed is shown in fg. 36.

In the Dune Park region there are a number of swainps upon
which dunes are advancing. While most of the vegetation is destroyed
at once, Salix glaucophylla, S. adenophylla, and Cornus stolonifera (Osier
dogwood) are able to adapt themselves to the new conditions, by elon-
gating their stems and sending out roots from the buried portions.
Thus hydrophytic shrubs are better able to meet the dune’s advance
successfully than any other plants. The water relations of these plants,
however, are not rapidly altered in the new conditions. It may be, too,
that these shrubs have adapted themselves to an essentially xerophytic
life through living in undrained swamps. Again, it may be true that
inhabitants of undrained swamps ate better able to withstand a partial
burial than are other plants. A swamp upon which a dune encroaches
is shown in fig. 35.

Vegetation appears to be unable to capture a rapidly moving dune.
While many plants can grow even on rapidly advancing slopes, they
do not succeed in stopping the dune. The movement of a dune is
checked chiefly by a decrease in the available wind energy, due to
increasing distance from the lake or to barriers. A slowly advancing
slope is soon captured by p.ants, because they have a power of verti-
cal growth greater than the vertical component of advance. Vege-

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CHICAGO AND VICINITY.

62 THE PLANT SOCIETIES OF

tation commonly gets its first foothold at the base of lee slopes about
the outer margin of the complex, because of soil moisture and protec-
tion from the wind. The plants tend to creep up the slopes by vege-
tative propagation. Antecedent and subsequent vegetation work
together toward the common end. Where there is no antecedent vege-
tation, Ammophila and other herbs first appear, and then a dense shrub
growth of Cornus, Salix, Vitis cordifolia (Frost grape), and Prunus Vir-
gintana (Chokecherry). Capture may also begin within the complex,
especially in protected depressions, where Sa@x longifolia is often
abundant.

D. The established dunes.—No order of succession in this entire
region is so hard to decipher as is that of the established dunes.
There are at least three types of these dunes so far as the vegetation is
concerned, and it is not yet possible to figure out their relationships.
The continuation of the conditions as outlined in the preceding para-
graph results in a forest society on the lee slope, in which is found the
basswood, together with a most remarkable collection of mesophytic
trees, shrubs, and climbers, which have developed xerophytic struc-
tures. These dunes are evidently but recently established, as is shown
by the absence of a. vegetation carpet; furthermore, the slopes are
almost always steep.

Again, there are forest societies in which the pines dominate, either
Pinus Banksiana or P. Strobus (White pine). These arise from a heath,
composed in the main of Arctostaphylos (Bearberry) and Juniperus.
The heath appears to originate on fossil beaches or on secondary .
embryonic dunes or other places where the danger of burial is
not great. It will be noted that both the heath and the pine forest are
dominated by evergreens. ‘These societies commonly occur near the
lake or on lakeward slopes, which are northern slopes as well. On
these coniferous dune slopes theresis to be found another notable col-
lection of northern plants, resembling ecologically the peat bog plants
already mentioned. Heaths and coniferous forests also occur on sterile
barren sand and in depressions where the conditions are unfavorable
for deciduous forests. A slight change in the physical conditions may
bring about the rejuvenation of the coniferous dunes, because of their
exposed situation. This rejuvenation commonly begins by the forma-
tion of a wind sweep, and the vegetation. on either hand is forced to
succumb to sand-blast action and gravity.

A third type of established dune is that in which the oaks pre-

4

CHICAGO AND VICINITY, - 63

dominate, and especially Quercus coccinea tinctoria. The oak dunes
are more common inland and on southern slopes. Probably the oaks
follow the pines, but the evidence’on which this is based is not volumi-
nous. The pines certainly have a wider range of habitat than the
oaks, occurring in wetter and in drier soil, and also in more exposed
situations. The mutual relations of the pines and oaks are certainly

Fic. 37.—Portion of an ancient beach line (Calumet beach) at Summit, showing the char-
acteristic oak vegetation, in this case chiefly bur oaks (Quercus macrocarpa).

interesting and deserve some very careful study. Pine forests prevail
on the north or lakeward slopes, and oak forests on the south or in-
land slopes. With the pines are other northern evergreen forms, such
as Arctostaphylos, while with the oaks are Opuntia, Euphorbia, and
other more southern types. The density of the vegetation on the
north side is also in contrast with the sparser and more open vegeta-
tion of the south side. The cause for this radical difference on the
two slopes is doubtless complex, but it is obvious that the north slope
has greater moisture, shade; and cold, and probably more wind.
Which of these is the more important is not certain, but the presence
of the northern aes seems in favor of cold or wind as the chief
factor.

64 THE PLANT SOCIETIES OF

There are a number of interesting sand hills and ridges at some
distance from the lake. Some of these are fifteen miles from the
present lake shore, while others are found at various intervals nearer
and nearer the lake. It has been found that these can be grouped for
the most part into three series, representing three beach lines of Lake
Chicago, as the glacial extension of Lake Michigan has been called.

Fic. 38.—Portion of an ancient beach (Glenwood beach) near Thornton. The trees here
are chiefly black oaks (Quercus coccinea tinctoria); the beach is higher, and the trees more
Juxuriant than usual.

The upper and oldest of these ridges has been termed the Glenwood
beach, the intermediate ridge the Calumet beach, and the lower and
younger ridge the Tolleston beach® The geographical relations of
these beaches is well discussed by Leverett, and also by Salisbury and
Alden, and nothing need be said here except as to the vegetation. In
general these ridges and hills have a xerophytic forest flora, dominated
by the bur, black, and white oaks (Quercus macrocarpa, Q. coccinea
tinctoria, Q. alba). The proportions between these trees varies strik-
ingly, though the bur or black oak is usually the chief character tree.
No satisfactory reason can yet be given for these variations, though
the bur oak appears to be more abundant on the lower and less
drained ridges, while the black oak is more abundant on the higher

CHICAGO AND VICINITY, 65

ridges. The shrub undergrowth is commonly sparse, and the most
frequent members of this stratum are the hazel (Corylus Americana),
Rosa, the New Jersey tea (Ceanothus Americanus), Salix humilis, the
low blueberry (Vaccinium Pennsylvanicum), and the huckleberry (Gay-
lussacia resinosa). Among the commoner herbs are Sr/ene stellata,
Antennarta plantaginifolia, Heuchera hispida, Rumex Acetosella (Field
sorrel) Carex Pennsylvanica, Potentilla argentea (Silvery cinquefoil), Poa
compressa, Pteris aguilina (Brake), Ceratodon purpureus. In open places
there are often almost pure growths of Poa or Potentilla. %gs. 3¢
and 35 show portions of these ancient beaches in which the oaks
dominate; fg. 34 shows, perhaps, the more common condition, 7. ¢.,
a rather low beach with a sparse tree growth.

The future of the vegetation on the established dunes and beaches
is somewhat problematical. From analogy with other plant societies
in this region, and from established dunes in Michigan, we should
expect a mesophytic forest, probably of the white oak-red oak-hickory
type at first, and then followed by a beech-maple forest. There are
evidences that some such changes are now taking place. On many
of the oak dunes, especially where protected from exposure, there is
already a considerable accumulation of humus. Herbaceous ravine
mesophytes, like Hepatica, Ariseema, and Trillium, are already present,
and with them mesophytic shrubs and trees, including the sugar maple
itself, though the beech has not been found on the dunes of our area, ,
as it has in Michigan. One might expect that the flora of the older
Glenwood beach would have advanced more toward the mesophytic
stage than has the flora of the younger Tolleston beach. Such, indeed,
seems to be the case, especially at Glenwood, where the white oaks are
more numerous, and the black oaks much larger and more luxuriant.
The humus is richer, and most things look as if the age of this beach
were notably greater than that of the Calumet or Tolleston beaches.
This subject, however, needs much further investigation. In any event,
one character of the ‘sand hill stands out in bold relief, viz., its great
resistance to physiographic change. Not only is its erosion slower than
that of the clay hill, but the advance of its vegetation is vastly slower
at all points along the line. The slowness of humus accumulation
accounts for this, perhaps, more than all else.

APPENDIX.

THE PRINCIPAL LOCALITIES ABOUT CHICAGO FOR THE STUDY
OF PLANT SOCIETIES.

In the following list of localities it will be convenient to discuss
the various districts about Chicago in regular order from north around
to southeast, using the various railroads and suburban street-car lines
as bases for discussion. The figures in parentheses after the various
towns indicate the railway mileage from the Chicago terminal station
of the particular railroad involved. References to pages are inserted,
showing where the various plant societies mentioned are described in
the body of the text. The accompanying maps show the geographic
and physiographic features of the places mentioned.

A number of the interesting localities about Chicago, as indicated
below, can be reached at small expense by utilizing the suburban
street-car lines. From the standpoint of expense, and often of con-
venience, though not of time, the street-car lines are perhaps the best
means of transportation for the points which they reach. However,
some of the railroads, notably the Illinois Central and the Chicago
Terminal Transfer, sell suburban tickets for but ‘slightly more than
street-car rates. Most of the railroads sell cheap ten and twenty-five
ride tickets, good for bearer, to the various points named below. ‘These
tickets are usually good for one year from date of sale, though on the
Michigan Central and Lake Shore and Michigan Southern railways
these tickets are good for but one month. On some railroads, especially
the Wabash, Chicago and Eastern Illinois, and Chicago, Rock Island
and Pacific, the above-named tickets are’ good until used. All of the
railroads inake rates for parties of sufficient size.

The places that can be reached by street-cars are briefly mentioned
in connection with the various railroads, but it may be well to: make a
general statement about the suburban street-car system of Chicago and
vicinity. “The Evanston street-car line pdsses near the dune, beach,
and swamp region about Edgewater.’ (See C., M. & St. P. below.)
The Chicago, Waukegan and Milwaukee car line reaches all the
districts along the north shore, as described on the line of the C. &
N. W. railway. The suburban service northwest is not good. Oak

66

APPENDIX. 67

HARTHOADE.

LEGEND.

Unsusmerceo Tice Areas.
= Titi Area of tHe Cuicaco Prain.
Sano anv Graver Deposits’ oF

Lake Guicaco.
SCALE oF MILES. ‘

Fic. 39.—Map showing the general distribution of the morainic uplands, prairie and swamp
areas, and postglacial beach deposits of the Chicago area (Salisbury and Alden).

68 APPENDIX.

Park, River Forest, and Maywood (see C. & N. W.) can be reached
by the Cicero and Proviso street-car line. The La Grange suburban
car line passes through Riverside and Grossdale (see C., B. & Q.).
The Chicago and Joliet line, southwest, reaches all points.described on
the C. & A. or A, T. & S. F. railways. On the south side, the
Chicago General and Chicago City railways run for a short distance
along the drainage canal. The Chicago City railway also reaches the
prairie districts west of Englewood (see C. T. T. and C. & G. T. rail-
ways). The Morgan Park and Blue Island street railway enters an
interesting territory (see C., R. I. & P.and C. T. T. railways). This
line now terminates at Harvey (I.C.R.R.). The Calumet street rail-
way reaches Hog Island (P., F. W. & C. Railway; Stony Island (reached
only by street-cars); Calumet lake, Pullman, and West Pullman (see
I.C. R. R.). The South Chicago city railway reaches Cheltenham
(I. C. R.R.), Irondale (Calumet lake and low prairies), Roby, Whiting,
Hammond, and East Chicago (P., F. W. & C. Railway); this last named
line traverses a country rich in lakes, swamps, and ancient beach lines.

Vorth.—The most interesting localities north of Chicago are along
the line of the Cu1caco anD NORTHWESTERN railway, Milwaukee divi-
sion; all of these points can also be reached by the Waukegan and
Milwaukee street-car line, which starts from Evanston. In the vicinity
of Rose Hill (8) and Rogers Park (9) there are numerous old beach
lines of the Tolleston stage, with their characteristic oaks (p. 64);
between the ridges are old lake basins, with peaty soil, commonly
utilized for truck farming. At W7rlmerfe (14) the ground is low and
flat, but well forested, with the characteristic trees of low moraines
(p. 48) and morainic swamps (p. 40). From Winnetka (17) to Lake
Bluff (30) there are magnificent places for study: clay ravines in all
stages of development (p. 13); lake bluffs, now naked, now grown. up
to shrubs and trees (p. 50) and upland morainic forests (p. 47). The
ravines and lake bluffs are particularly fine, and are nowhere else so
well developed. West of Winnetka and Glencoe is Skokie marsh,
which shows all the stages between swamp and prairie (p. 35). North
and south of Waukegan (36) are small but interesting dunes (p. 57)
and many dying pondsand swamps; an ancient lake bluff at this point
also presents interesting features.

At Edgewater (7), which may be reached by the Cuicaco, MIL-
WAUKEE AND St. Pau railway, Evanston line, or by the Chicago and
Evanston street-car line, there are some excellent dunes with a natural

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1 APPENDIX. : 69

vegetation (p. 57), also old beach lines (p.64), and dying swamps
(p. 35). Along the Milwaukee division of the C., M. & St. P. railway,
there are good opportunities for the study of the river series along the
north branch of Chicago river. There is an excellent flood plain
forest (p. 22) at Forest Glen (10), and from here to Oak Glen (16)
there are good river conditions, and also upland forests. Two miles
west of Deerfield (24) there is an extensive forested country, oaks domi-
nating for the most part, but with many maples towards the Desplaines
river (p. 49).

Northwest.—The Wisconsin CENTRAL railway runs rather close to .
the Desplaines river for many miles; studies of flood plain forests
(p. 25) may be made by walking about a mile east at Franklin Park
(15), Desplatnes (23), Wheeling (30), and Pratrie View (34). From
this latter point the splendid forests referred to in the preceding para-
graph can be reached as conveniently as from Deerfield. The Cuicaco
AND NORTHWESTERN railway, Wisconsin division, crosses the Desplaines
river at Desplaines (17), at which point there is a fair place for flood
plain study. At Barrington (32) there are interesting morainic forests;
three miles northeast is Lake Zurich.

The most interesting country northwest of the city is along the
CuHicaGo, MILWAUKEE AND ST. Paut railway, Elgin line. At Gale-
wood (9) the Glenwood beach is very prominent, and a marked con-
trast is shown between the tree vegetation of the beach (p. 64), and the
prairie to the east (p. 42). West of Glendon Park (12), where the
railroad crosses Desplaines river, is one of the finest forest districts
near Chicago; the flood plain flora (p. 25) merges gradually into the
flora of the flat moraine (p. 48), with morainic swamps (p. 40). At
Woodale (19) the railroad crosses Salt.creek; along this stream there
are upland forests (p. 47), as well as various phases of stream vegeta-
tion. There are extensive morainic forests with oaks and hickories
west of Bartlett (30).

West-—The CuicaGo anD NORTHWESTERN railway, Galena division,
passes through an extensive prairie district in the west part of Chicago,
now largely built up. The Calumet beach is crossed at Auszin (7) and
the Oak Park spit at Oak Park (8), but the original oak vegetation has
largely been destroyed. At River Forest (10) an excellent flood plain
forest is still preserved (p. 25). Northwest of E/mhurst (16) there are
some morainic forests (p. 47), which grade into flood plain forests along
Salt creek. Near Glen Ellyn (22) there are interesting morainic for-

a APPENDIX.

ests, especially in association with the east branch of Dupage river.
The places mentioned in this paragraph, except Elmhurst and Glen
Ellyn, can be reached by street-cars,

The Cuicaco Great WESTERN railway passes through essentially
the same territory as the Chicago and Northwestern. The Oak Park
spit is crossed at Forest Home (10), and the natural vegetation shows
fairly well at this point (p. 64). The Desplaines river is crossed
between Forest Home and Maywood, but the flood plain vegetation has
been somewhat altered by artificial agencies. The morainic country
west of Maywood (12) is largely tilled. The ILL1nois CENTRAL railroad,
Omaha line, also passes through the country just described. Interest-
ing studies of the first vegetation on clay soil (p. 48) can be made along
the drainage canal at Lawndale Ave. (7), Crawford Ave. (8), or Hyman
Ave. (9); this part of the canal can also be reached by the street-car
lines. The Calumet beach, which shows the usual oak vegetation (p. 64),
is crossed at Parkway Ave. (12). At Worth Riverside (13) the Des-
plaines is crossed and a good flood plain forest can be observed (p. 25).
At Hillside (17) there is a limestone cut, a rare feature about Chicago;
rock vegetation (p. 44) can be finely studied here. From Addison (24)
the forests along Salt creek, referred to in the preceding paragraph,
can be easily reached.

The Cuicaco, BURLINGTON AND QuINCy railroad passes through a
country of much interest. Extensive prairies are seen from Chicago
to Riverside (11); at this latter place is a splendid field for study, the
bottoms of the Desplaines river being covered with a luxuriant flood
plain forest (p.25). On the east bank of the river the Calumet beach
(p. 64) and the xerophytic river banks (p. 18) show the usual features.
At East Grossdale (12) the Salt creek flood plains may be seen; this
stream empties into the Desplaines about half a mile from the station.
Between Western Springs (15) and Hinsdale (17) is an excellent region
for study; the headwaters of Flag creek are in a rather poorly drained
swamp (p. 35); west of this is a typical morainic topography with con-
siderable areas of forest (p. 47). North of Hinsdale there are also
morainic forests and a number of interesting places along Salt creek.
Morainic forests with maples as well as oaks may be seen at Dow-
ner’s Grove (21). There are forests along the branches of the Dupage
river at Lisle (24) and Maperville ( 28).

Southwest.—The CHICAGO AND ALTON railway, the Atcuison, To-
PEKA AND Santa FE railway and the Chicago and Joliet street-ear

APPENDIN. 71

line pass through identical territory and may be considered together.
The drainage canal is accessible for its entire length on all of these
lines. Within the city limits, especially near Corwith (7), the develop-
ment of a new vegetation can be well studied on the great clay piles
along the canal (p. 48). From Summit (12) to Joliet (37) the railroads
follow the Desplaines river, as well as the canal, and at various points
the underlying limestone comes closer to the surface than is usually
the case, permitting the study of its influence on the vegetation (p. 44).
At Summit the Calumet beach shows the characteristic beach line vege-
tation (p. 64). At Willow Springs (18) is an excellent place for the
study of morainic forests (p. 47), ravines (p. 13), and flood plain vege-
tation (p. 22). The rock débris from the canal has an interesting
vegetation here also. At Sag Bridge (22), besides the morainic for-
ests, the difference between the well-drained plant societies along the
river and the poorly drained societies (p. 35) along the Feeder is well
shown. The vegetation of rock outcrops can be especially well seen
near Lemont (25). Along Fraction run, a mile south of Lockport (33),
are to be seen perhaps the best rockbound ravines near Chicago (p._);
the beginnings of the flood plain vegetation are well shown here, as
well as the later stages along the river (p. 15).

The WasasH railway, St. Louis line, passes through the usual
prairie district (p. 42) between Englewood (7) and Oak Lawn (15); at
this latter place the Calumet beach is crossed and the characteristic
trees may Le seen (p. 64). Between Oak Lawn and Worth (18) the
Feeder is crossed, which shows the transitions between swamp and
prairie (p. 35). At Worth morainic forests occur, although this area
was submerged in the earlier lake stages. South of Worth there are
more areas of swamp and prairie along a tributary of the Feeder, also
a beach line with the customary oaks. At Palos Springs (20) is one of
the finest places in the Chicago area for the study of all phases of
vegetation in a morainic region which has been eroded. About two
miles northwest of the station are to be seen all types of morainic for-
ests (p. 47) and morainic swamps (p. 40). All phases of river activity
from the ravine to the flood plain may also be studied here (p. 13). A
short distance north is the Sag, with its extensive swamps. At Orland
(24) and Alpine (27) the morainic societies are also well developed.

The Cuicaco, Rock IsLanD AND Paciric railway crosses the Calu-
met beach at Washington Heights (13), at which point the oak vegeta-
tion is well developed (p. 64). This beach is followed to Blue Jsland

72 APPENDIX.

(16); otherwise the vegetation between Englewood and Blue Island is
chiefly prairie. A branch line of this railroad passes through Beverly
Hills and Morgan Park, joining the main line again at Blue Island.
All along this branch there are fine opportunities for the study of
morainic forests (p. 47), beach line forests, and prairies. At Beverly
Hills (12) there are interesting ravines (p. 13), and also a fairly well
developed flood plain (p. 22). All the points thus far mentioned in
this paragraph, except Beverly Hills, can be reached by street-cars.
Beyond Blue Island are low prairies. At Dupont (21) sharp transitions
are seen between the prairie, beach line, and morainic forest. At
Tinley Park (23) and Mokena (30) are morainic forests (p 47). Vew
Lenox (34) is an excellent place for study, showing morainic forests of
the maple type as well as oak, and also fine flood plain forests along
Hickory creek. This railroad furnishes the most direct route to
Starved Rock, Utica (94); see pp. 15, 20, 24.

South.—The ILtinois CENTRAL railroad, main line south, crosses a
region of swampy prairie between Grand Crossing (9) and Burnside
(12); at this latter place the Tolleston beach is crossed, showing the
typical vegetation (p. 64). Pud/man (14) is perhaps the most convenient
point from which to study Lake Calumet, together with the swamp and
prairie derived therefrom (p. 33). At Riverdale (17) the Little Calumet
river, which shows flood plain forests (p. 22) and xerophytic bluffs (p. 18),
is crossed, as is also the Tolleston beach for the second time. At
North Harvey (19) the river is again crossed. In the neighborhood of
Harvey (20) are extensive prairies. Between Haze/ Crest (22) and Home-
wood (23) the Calumet and Glenwood beaches are crossed, showing
very interesting conditions, especially east of Homewood; ancient
dunes of considerable size and dying peat bogs (p. 39) are found in
profusion. South of //ossmoor (25) morainic (p. 47) and flood plain
forests are well shown along Butterfield creek. The Blue Island
branch of the I. C. R. R. passes through West Pullman (17), where
are to be found splendid illustrations of beach line vegetation, and
also undrained swamps; about a mile to the south is the Little Calumet
river, with a well developed flood plain forest. The South Chicago
branch of this railroad crosses numerous recent beach lines, and at
Cheltenham (11) runs close to the lake shore, where a recent beach and
dune flora (p. 56), and also the vegetation of a rocky shore, may be
studied. All the places named in this paragraph can be reached by
street-cars, except Riverdale, Hazel Crest, Homewood, and Flossmoor.

APPENDIX. 73

The Cuicaco anp Eastern Iuinois railroad. At Auburn Park
(9) the Tolleston beach shows the usual beach features (p. 64). A low
prairie is crossed beyond Kensington (14). At Dolton (17) the same
features are shown as at Riverdale (I. C. R. R.). Near South Holland
(19) are extensive low prairies, also the Little Calumet river, with low
xerophytic bluffs. Zhornton (22) and Glenwood (23) are points of
great interest; nowhere about Chicago are there to be found better
illustrations of. the various phases of stream history than along Thorn
creek (pp. 19, 25). West of Thornton are the ancient dunes and
swamps already mentioned (see Homewood, I. C. R. R.). At Chicago
Heights (27) there are morainic forests (p. 47) and swamps (p. 40), and
also the various stream phases.

The Cuicaco TERMINAL TRANSFER railroad crosses the prairie dis-
trict west of Englewood. ‘At Sixty-ninth street (also reached by street-
cars), isone of the best places for a prairie study (p. 42). Between
Ninety-first street and Morgan Park morainic swamps (p. 40) and
forests (p. 47) are well displayed. West of Morgan Park there are
interesting ancient dunes and beach lines (p. 64), which mayv also be
reached by street-cars. This road then passes through Blue Island,
Harvey (see I. C. R. R.), Glenwood, and Chicago Heights (see C. & E.
I. R. R.).

The Cuicaco, INDIANAPOLIS AND LOUISVILLE railway (Monon
Route) follows along the Tolleston beach between Auburn Park and
Burnside, passes near Suny [sland (p. 44); this interesting point can be
conveniently reached only by street-cars; then through extensive low
prairies to the east of Lake Calumet. After crossing the Calumet
river, beach lines and swamps are seen on all sides (see Hegewisch
and Hammond, P., F. W. & C. Railway). Beyond Hammond (21), also
reached by street-cars, are many oak-clad ridges (p. 64) and undrained
swamps (p. 35), mostly connected with the Tolleston beach. South of
the Little Calumet river the Calumet beach line is crossed near May-
nard; south of Maynard (26) are great areas of swamp and prairie.
At Dyer (29) the Glenwood beach, with interesting ancient dunes, is
seen. Beyond this are extensive morainic forests (p. 47). At Cedar
Lake (40) lake and forest vegetation are well shown.

Southeast. — THE CuHicaco AND GRAND TRUNK railway passes
through much the same country as the C. T. T. R. R. (see above)
between Chicago and Blue Island. All types of prairie vegetation are
excellently shown at Chicago Lawn (10), also reached by street-cars.

74 APPENDIN.

Beyond Blue Island this road passes through Harvey (see I. C. R. R.),
and crosses Thorn creek (see C. & E.I.R.R.). At Oak Glen (28) the
Calumet beach shows ancient dunes with the usual vegetation (p. 62).
Beyond Maynard (31) are extensive swamps. At Griffith (36) are
beach lines, and at Azwsworth (45) and beyond this road passes through a
morainic country.

The PitTTspurG, CINCINNATI, CHIcaGo aNnD St. Lours railway
(Pan Handle Route) traverses the prairie district west of Engle-
wood, crosses beach lines at Washington Heights (see C., R. I.
& P. Ry.), West Pullman and Riverdale (see I. C. R. R.), and
Dolton (see C. & E. I. R. R.). After crossing the Little Calumet
river the Calumet beach is quickly reached at Lansing (27; see
Oak Glen, C. & G. T. Ry.). Beyond Maynard (29) are swamps and
low prairies, and at Schererville (34) are extremely interesting ancient
dunes connected with the Glenwood beach. Beyond this the country
is morainic.

The Cuicaco anp Erte railroad uses the the same tracks as the C.
I. & L. as far as Hammond (21). Beyond Hammond, also, the same
features are to be seen as on the road just mentioned. ‘The Calumet
beach is crossed at Highlands (26), and beach lines are well developed
at Griffith (29).

The Pirrspurc, FortT WayNE AND Cuicaco (Pennsylvania) rail-
way. At Constance (11) are extensive prairies, showing the stages of
development (p. 42); Hog Island, with a small area of morainic swamp
"forest (p. 40) is a short distance southwest. At Rody (15) Wolf lake
shows all stages of development between lake and prairie, as at Calu-
met lake (I. C. R. R.}; there are also many beach lines with oaks in
this neighborhood (p. 64). Constance and Roby can also be reached
by street-cars. Between Whiting (17) and Hobart (34) this railroad
crosses a great number of swamps*and beach lines. Among the best
places for study are Clarke (24), where forested beach lines and
undrained swamps are finely shown; the Grand Calumet river is close
by, with a rich aquatic and marginal vegetation. ‘The Tolleston beach
line is well displayed at Zolleston (27), and the Calumet beach may be
seen at Liverpool (31). A branch line of the P., F. W.& C. Ry.
passes through Hegewzsch (18), from which place Wolf lake (see
above) and various beach lines can be studied. Hammond (22) and
Last Chicago (23), also reached by street-cars, are the best places near
Chicago for studying the typical swamps and sandy ridges of the dune

APPENDIX. 75

region; Grand Calumet river, with its interesting aquatic and marsh
vegetation, is accessible from either town. .

The New York, Cuicaco anp St. Louis (Nickel Plate) railroad
passes through the same territory as the C. I. & L. as far as Ham-
mond, but has a station at Hegewisch (see P., F. W. & C. Ry.). The
country beyond Hammond has the beach lines and swamps as described
on other roads. The swamps and ancient dunes are well displayed at
Glen Park (30). West of Hodarr (35) is an interesting morainic island
in the lake plain.

The LakE SHORE AND MICHIGAN SOUTHERN railway passes through
one of the most interesting districts about Chicago, and is the most
convenient route to the dune region. As far as Whiting this road runs
parallel to the P., F. W. & C. Ry. Beyond Whiting (17) are many
low sand ridges with pines and depressions with water lilies; farther
on are higher ridges with oaks (p. 62) and depressions with swamps
(p. 35) instead of pools; these types of vegetation can be well studied
at Pine (23). Miller (30) is a place of great interest, showing living
dunes and the rich aquatic and marsh vegetation of Grand Calumet
river (p. 41) to the north, the ancient dunes of the Tolleston beach,
Cassandra and tamarack swamps to the south and southeast. Dune
Park (35) is far the best place to study living dunes in all phases (p.
57); established dunes and undrained swamps are also well displayed
at this point. Chesterton (41) is, all things considered, the most inter-
esting place in the vicinity of Chicago, since it shows types of nearly
all plant societies discussed in this paper; all phases of the river series
from the ravine to the flood plain; all stages from pond to prairie;
all types of dune activity, past and present; and morainic forests.
Spring brooks are best shown at this point, also the beech-maple
forests.

The Micuican CENTRAL railway diverges from the I. C. R. R. at
Kensington (13), passes across the swamps and prairies associated with
Lake Calumet, crosses an oak ridge and Little Calumet river. Beyond
Hammond (20) are the numerous swamps and ridges as described
above. At TZolleston (29) the Tolleston beach is finely displayed
(p. 62), and a remarkably sharp transition is shown between this
ancient line of dunes and the broad marshes associated with the Little
Calumet river (p. 41). At Zake (35) the Calumet beach and Deep
river are interesting fields for study; the railroad follows the beach
line for a number of miles. Por¢er (44) corresponds with Chesterton

46 APPENDIX.

on the L. S.& M.S. Railway (q. v.), and isa place of the greatest
botanical and physiographic interest. Between Porter and Michigan
City (56) the railroad crosses a peninsular portion of morainic terri-
tory and then follows somewhat closely the present shore, affording a
splendid view of the dunes.

The BaLTIMORE AND Ouio railroad passes through the same general
territory asthe L. S. & M. S. Railway between Whiting (25) and
Miller (38); see above), but somewhat nearer the.lake. Dunes, both
living and dead, as well as swamps, can be seen at Ldgemoor (30) and
Grand Calumet Heights (35). Beyond Miller this road passes through
a very interesting swamp region, including Cassandra and tamarack
swamps (p. 35); ancient dunes of the Tolleston and Calumet beaches
are also well displayed.

‘The Wazasu railway, Buffalo line, uses the same tracks as the C., I.
& L. Railway to Hammond (21); here, as well as at Last Chicago (22)
‘and TZolleston (29), the conditions are as noted above for the P. F. W.
& C. Railway. Ae¢na (33) corresponds to Miller on the L. S. & M.
S. Railway. Near Crocker (42) the various stream phases (p. 13) are well
illustrated along Salt creek.

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