James G. (James George) Needham.

The life of inland waters; an elementary text book of fresh-water biology for students online

. (page 6 of 26)
Online LibraryJames G. (James George) NeedhamThe life of inland waters; an elementary text book of fresh-water biology for students → online text (page 6 of 26)
Font size
QR-code for this ebook

plants, such as cat-tail, rushes and sedges; of a swamp
as a wet area overgrown with trees ; and of a bog as such
an area overgrown with sphagnum or bog-moss, and
yielding under foot. The great Montezuma Marsh o'f
Central New York (shown in the initial above) is


9O Types of Aquatic Environment

typical of the first class ; the Dismal Swamp of eastern
Virginia, of the second; and over the northern lake
region of the continent there are innumerable examples
of the third. These types are rarely entirely isolated,
however, since both marsh and bog tend to be invaded
by tree growth at their margins. Such wet lands occupy
a superficial area larger by far than that covered by
lakes and rivers of every sort. They cover in all
probably more than a hundred million acres in the
United States; great swamp areas border the Gulf
of Mexico, the South Atlantic seaboard, and the lower
reaches of the Mississippi, and of its larger tributaries,
and partially overspread the lake regions of upper
Minnesota, Wisconsin, Michigan and Maine. In the
order of the areas of " swamp land" (officially so desig-
nated) within their borders the leading states are
Florida, Louisiana, Arkansas, Mississippi, Michigan,
Minnesota, Wisconsin and Maine.

Swamps naturally occupy the shoal areas along the
shores of lakes and seas. Marine swamps below mean
tide occur as shoals covered with pliant eel-grass.
Above mean tide they are meadow-like areas located
behind protecting barrier reefs, or they are mangrove
thickets that fringe the shore line, boldly confronting
the waves. With these we are not here concerned.
Fresh -water marshes likewise occupy the shoals border-
ing the larger lakes, where protected from the waves by
the bars that mark the shore line. In smaller lakes,
where not stopped by wave action, they slowly invade
the shoaler waters, advancing with the filling of the
basin, and themselves aiding in the filling process.

That erosion sometimes gives rise to lakes has
already been pointed out; much oftener it produces
marshes; for depositions of silt in the low reaches of
streams are much more likely to produce shoals than
deep water.

Cat-Tail Marshes

Cat-tail Marshes In the region of great lakes every
open area of water up to ten feet in depth is likely to
be invaded by the cat -tail flag (Typha). The ready
dispersal of the seeds by winds scatters the species
everywhere, and no permanent wet spot on the remotest
hill-top is too small to have at least a few plants. Along

FIG. 26. An open-water area (Parker's Pond) in the Montezuma Marsh in
Central New York. Formerly it teemed with wild water fowl. It is sur-
rounded by miles of cat-tail flags (Typha) of the densest sort of growth.

the shores of the Great Lakes and in the broad shoals
bordering on the Seneca River there are meadow-like
expanses of Typha stretching away as far as the eye
can see. Many other plants are there also, as will be
noted in a subsequent chapter, but Typha is the
dominant plant, and the one that occupies the fore-
front of the advancing shore vegetation. It masses its
crowns and numberless interlaced roots at the surface

92 Types of Aquatic Environment

of the water in floating rafts, which steadily extend into
deeper water. The pond in the center of Montezuma
Marsh shown in the preceding figure is completely
surrounded by a rapidly advancing, half -float ing even-
fronted phalanx of cat-tail.

FIG. 27. "The Cove" at the Cornell University Biological Field Station, in
time of high water. Early summer. Two of the University buildings
appear on the hill in the distance.

Later conditions in such a marsh are those illustrated
by our frontispiece : regularly alternating spring floods,
summer luxuriance, autumn burning and winter freez-
ing. This goes on long after the work of the cat-tail,
the pioneer landbuilding, has been accomplished.
The excellent aquatic collecting ground shown in the
accompanying figure is kept open only by the annual
removal of the encroaching flag.

Okefenokee Swamp


The Okefenokee Swamp. In southern Georgia lies
this most interesting of American swamps. It is
formed behind a low barrier that lies in a N., N. E.
S., S. W. direction across the broad sandy coastal plain,
intersecting the course of the southernmost rivers of

FIG. 28. A view of "Chase's Prairie" in the more open eastern portion of the
Okefenokee Swamp, taken from an elevation of fifty feet up a pine tree on
one of the incipient islets. The water is of uniform depth (about four or
five feet). This is one of the most remarkable landscapes in the world.

Photo by Mr. Francis Harper.

Georgia that drain into the Atlantic. Behind the bar-
rier the waters coming from the northward are retained
upon a low, nearly level plain, that is thinly overspread
with sand and underlaid with clay. They cover an
area some forty miles in diameter, hardly anywhere too
deep for growth of vascular plants. There is little dis-
coverable current except in the nascent channels of the

94 Types of Aquatic Environment

two outflowing streams, St. Mary's and Suwannee
Rivers. The waters are deeper over the eastern part of
the swamp, the side next the barrier; and here the
vegetation is mainly herbaceous plants, principally
submerged aquatics, with occasional broad meadow-
like areas overgrown with sedges. These are the so-
called * 'prairies." The western part of the swamp
(omitting from consideration the islands) is a true
swamp in appearance being covered with trees, prin-
cipally cypress. A few small strips of more open and
deeper water (attaining 25 feet) of unique beauty,
owing to their limpid brown waters and their setting
of Tillandsia-covered forest, are called lakes.

The whole swamp is in reality one vast bog. Its
waters are nearly everywhere filled with sphagnum.
Whatever appears above water to catch the eye of the
traveler, whether cypress and tupelo in the western part
or sedges and water lilies on the "prairie," everywhere
beneath and at the surface of the water there is sphag-
num ; and it is doubtless to the waterholding capacity
of this moss that the relative constancy of this great
swamp on a gently inclined plain near the edge of the
tropics, is due.

Climbing bogs In-so-far as swamps possess any basin
at all they approximate in character to shallow lakes;
but there are extensive bogs in northern latitudes that
are built entirely on sloping ground; often even on
convex slopes. These are the so-called "climbing
bogs." They belong to cool-temperate and humid
regions. They exist by the power of certain plants,
notably sphagnum, to hold water in masses, while
giving off very little by evaporation from the surface.
A climbing bog proceeds slowly to cover a slope by the
growth of the mass of living moss upward against
gravity, and in time what was a barren incline becomes
a deep spongy mass of water soaked vegetation.

Conditions in Swamps 95

Conditions of life In the shoal vegetation-choked
waters of marshes there is little chance for the formation
of currents and little possibility of disturbance by wind.
Temperature conditions change rapidly, however, owing
to the heat absorbing and heat radiating power of the
black plant -residue. The diurnal range is very great,
water that is cool of a morning becomes repellantly hot
of a summer afternoon. Temperatures above 90 F.
are not then uncommon. Unpublished observations
made by Dr. A. A. Allen in shoal marsh ponds at the
Cornell Biological Field Station throughout the year
1909, show a lower temperature at the surface of the
water than in the bottom mud from December to April,
with reverse conditions for the remainder of the year.
The black mud absorbs and radiates heat rapidly.

Conditions peculiar to marshes, swamps and bogs are
those due to massed plant remains more or less per-
manently saturated with water. Water excludes the
air and hinders decay. Half disintegrated plant
fragments accumulate where they fall, and continue
for a longer or shorter time unchanged. According to
their state of decomposition they form peat or muck.

In peat the hard parts and cellular structure of the
plant are so well preserved that the component species
may be recognized on microscopic examination. To
the naked eye broken stems and leaves appear among
the finer fragments, the whole forming a springy or
spongy mass of a loose texture and brownish color.
The color deepens with age, being lightest immediately
under the green and living vegetation, and darkest in
the lower strata, where always less well preserved.

The water that covers beds of peat acquires a brown-
ish color and more or less astringent taste due to in-
fusions of plant-stuffs. Humous acids are present in
abundance and often solutions of iron sulphate and
other minerals.

96 Types of Aquatic Environment

Muck is formed by the more complete decay of such
water plants as compose peat. The process of decay is
furthered either by occasional exposure of the beds to
the air in spells of drought, or by the presence of lime
in the surrounding soil, correcting the acidity of the
water and lessening its efficiency as a preservative.
Muck is soft and oozy, paste-like in texture and black
in color. In the openings of marshes, like that shown
on page 89 are beds of muck so soft that he who ven-
tures to step on it may sink in it up to his neck. In
such a bed the slow decomposition that goes on in hot
weather in absence of oxygen produces gases that
gather in bubbles increasing in size until they are able
to rise and disrupt the surface.* So are formed marsh
gas (methane) which occasionally ignites spontaneously,
in mysterious flashes over the water the well known
"Jack-o-lantern" or "Will-o-the-wisp" or "Ignis
fatuus" and hydrogen sulphide which befouls the sur-
rounding atmosphere.

The presence in marsh pools of these noxious gases,
of humous acids, and of bitter salts, and of the absence
of oxygen except at the surface, limits their animal
population in the main to such creatures as breathe air
at the surface or have specialized means of meeting
these untoward conditions.

High and Low Water Swamps being the shoalest of
waters are subject to the most extreme fluctuations.
That they retain through most dry seasons enoug"h
water for a permanent aquatic environment is largely
due to the water-retaining power of aquatic plants.
Notable among these is sphagnum, which holds en-
meshed in its leaves considerable quantities of water,
lifted above the surrounding water level. Aquatic seed

*See Penhallow, "A blazing beach" in Science, 22:794-6, 1905.

High and Low Water


plants, also, whose stems in life are occupied with
capacious air spaces, fill with water when dead and
fallen, and hold it by capillarity. So, they too, form
in partial decay a soft spongy water-soaked ground

Marshes develop often a wonderful density of popu-
lation, for they have at times every advantage of water,
warmth and light. The species are fewer, however,
than in the more varied environment of land. Com-
paratively few species are able to maintain themselves
permanently where the pressure for room is so great
when conditions for growth are favorable, and where
these conditions fail more or less completely every dry
season. Aquatic creatures that can endure the condi-
tions shown ^^ in the accompanying figure
must have ^feSf A& specialized means of tiding
over the ^vYTf J&t period of drouth.

FIG. 29. The bed of a marsh pool in a dry season, showing deep mud cracks,
and a thin growth of bur-marigold and spike-rush.

Life of Inland Waters


From a Report by the senior author. By
Courtesy of the New York Conservation Commission


A A. Well-lighted surface water
B. The breaker line

>c C. The level of the pond

D. The level of the Nitella

E. The region of disappear
ance of all growths of
green plants

F. The region of total dark-


IS the testimony of all
biology that the water
was the original home of
life upon the earth.
Conditions of living are
simpler there than on
the land. Food tends
to be more uniformly dis-
tributed. The perils of
evaporation are absent.
Water is a denser medi-
um than air, and sup-
ports the body better, and there is, in the beginning,
less need of wood or bone or shell or other supporting
structures. Life began in the water, and the simpler
forms of both plants and animals are found there still.
But not all aquatic forms have remained simple.
For when they multiplied and spread and filled all the
waters of the earth the struggle for existence wrought
diversification and specialization among them, in water
as on land. The aquatic population is, therefore, a
mixture of forms structurally of high and low degree.
All the types of plant and animal organization are
represented in it. But they are fitted to conditions so
different from those under which terrestrial beings live
as to seem like another world of life.


loo Aquatic Organisms

The population of the water includes besides the
original inhabitants those tribes that have always
lived in the water a mixture of forms descended from

ancestors that once lived on
land. The more primitive
groups are most persistently
aquatic. Comparatively few
members of those groups that
have become thoroughly fit-
ted for life on land have re-
turned to the water to live.


I VERY large group of plants
has its aquatic members.
The algae alone are predomi-
nantly aquatic. Most of them live wholly immersed;
some live in moist places, and a few in dry places,
having special fitnesses for avoiding evaporation. In
striking contrast with this, all the higher plants, the
seed plants, ferns, and mosses, center upon the land,
having few species in wet places and still fewer wholly
immersed. Their heritage of parts specially adapted
to life on land is of little value in the water. Rhi-
zoids as foraging organs, a thick epidermis with auto-
matic air pores, and strong supporting tissues are little
needed under water. These plants have all a shore-
ward distribution, and do not belong to the open water.
Only algae, molds and bacteria are found in all waters.

The Algae 101


It is a vast assemblage of plants that makes up this
group; and they are wonderfully diverse. Most of
them are of microscopic size, and few of even the larger
ones intrude upon our notice. Notwithstanding their
elegance of form, their beauty of coloration and their
great importance in the economy of water life, few of
them are well known. However, certain mass effects
produced by algae are more or less familiar. Massed
together in inconceivably vast numbers upon the sur-
face of still water, their microscopic hosts compose the
* 'water bloom. ' ' Floating free beneath the surface they
give to the water tints of emerald* of amberf or of
blood t. Matted masses of slender green filaments
compose the growths that float on oxygen bubbles to
the surface in the spring as "pond scums." Lesser
masses of delicately branched filaments fringe the
rocky ledges in the path of the cataract, or encircle sub-
merged sticks and piling in still waters. Mixtures of
various gelatinous algae coat the flat rocks in clear
streams, making them green and slippery; and a rich
amber-tinted layer of diatom ooze often overspreads the
stream bed in clear waters.

These are all mass effects. To know the plants com-
posing the masses one must seek them out and study
them with the microscope. Among all the hosts of
fresh water algae, only a few of the stoneworts (Char-
aceae) are in form and size comparable with the higher

Many algae are unicellular; more are loose aggre-
gates of cells functioning independently; a few are
well integrated bodies of mutually dependent cells.

*Volvox in autumn in waters over submerged meadows of water weed.

tDinobryon in spring in shallow ponds.

\Trichodesmium erythraum gives to the Red Sea the tint to which its
name is due. The little crustacean, Diaptomus, often gives a reddish tint to
woodland pools.

IO2 Aquatic Organisms

The cells sometimes form irregular masses, with more or
less gelatinous investiture. Often they form simple
threads or filaments, or flat rafts, or hollow spheres.
Algal filaments are sometimes simple, sometimes
branched; sometimes they are cylindric, sometimes
tapering ; sometimes they are attached and grow at the
free end only ; sometimes they grow throughout ; some-
times they are free, sometimes wholly enveloped in
transparent gelatinous envelopes. And the form of the
ends, the sculpturing and ornamentation of the walls and
the distribution of chlorophyll and other pigments are
various beyond all enumerating, and often beautiful
beyond description. We shall attempt no more, there-
fore, in these pages than a very brief account of a few
of the commoner forms, such as the general student of
fresh water life is sure to encounter; these we will
call by their common names, in so far as such names
are available.

The flagellates We will begin with this group of
synthetic forms, most of which are of microscopic size
and many of which are exceedingly minute. That
some of them are considered to be animals (Mastigo-
phora) need not deter us from considering them all
together, suiting our method to our convenience. The
group overspreads the undetermined borderland be-
tween plant and animal kingdoms. Certain of its
members (Euglena) appear at times to live the life of a
green plant, feeding on mineral solutions and getting
energy from the sunlight; at other times, to feed on
organic substances and solids like animals. The more
common forms live as do the algae. All the members of
the group are characterized by the possession of one or
more living protoplasmic swimming appendages, called
flagella, whence the group name. Each flagellum is
long, slender and transparent, and often difficult of



observation, even when the jerky movements of the
attached cell give evidence of its presence and its
activity. It swings in front of the cell in long serpen-
tine curves, and draws the cell after it as a boy's arms
draw his body along in swimming.

Many flagellates are permanently unicellular; others
remain associated after repeated divisions, forming
colonies of various forms, some of which will be shown in
accompanying figures.

Carteria This is a very minute flagellate of spherical
form and bright green in color (fig. 300). It differs
from other green flagellates in having four flagella : the
others have not more than two. It is widely distrib-
uted in inland waters, where it usually becomes more
abundant in autumn, and it appears to prefer slow
streams. Kofoid's notes concerning a maximum occur-
rence in the Illinois River are well worth quoting :

"The remarkable outbreak of Carteria in the autumn
of 1907 was associated with unusually low water, and

IO4 Aquatic Organisms

concentration of sewage, and decrease of current. The
water of the stream was of a livid greenish yellow tinge.
The distribution of Carteria in the river was
remarkable. It formed great bands or streaks visible
near the surface, or masses which in form simulated
cloud effects. The distribution was plainly uneven,
giving a banded or mottled appearance to the stream.
The bands, 10 to 15 meters in width, ran with the
channel or current, and their position and form were
plainly influenced by these factors. No cause was
apparent for the mottled regions. This phenomenon
stands in somewhat sharp contrast with the usual
distribution of waterbloom upon the river, which is
generally composed largely of Euglena. This presents
a much more uniform distribution, and unlike Carteria,
is plainly visible only when it is accumulated as a super-
ficial scum or film. Carteria was present in such quan-
tity that its distribution was evident at lower levels so
far as the turbidity would permit it to be seen. It
afforded a striking instance of marked inequalities in

Similar green flagellates of wide distribution are
Chlamydomonas and Sphaerella (fig. 306) commonly
found in rainwater pools.

Certain aggregates of such cells into colonies are very
beautiful and interesting. Small groups of such green
cells are held together in flat clusters in Gonium and
Platydorina, or in a hollow sphere, with radiating
flagella that beat harmoniously to produce a regular
rolling locomotion in Pandorina (fig. 30 e), Eudorina
and Volvox.

Volvox The largest and best integrated of these
spherical colonies is Volvox (fig. 31). Each colony may
consist of many thousands of cells, forming a sphere
that is readily visible to the unaided eye. It rotates

Volvox 105

constantly about one axis, and moves forward therefore
through the water in a perfectly definite manner.
Moreover, the "eye spots" or pigment flecks of the
individual cells are larger on the surface that goes fore-

FIG. 31. Volvox, showing young colonies in all stages of development.

most. Sex cells are fully differentiated from the
ordinary body cells. Nevertheless, new colonies are
ordinarily reproduced asexually. They develop from
single cells of the old colony which slip inward some-
what below the general level of the body cells, repeat-
edly divide, (the mass assuming spherical form),
differentiate a full complement of flagella, a pair to each
cell, and then escape to the outer world by rupturing
the gelatinous walls of the old colony. Many develop-


Aquatic Organisms

ing colonies are shown within the walls of the old ones
in the figure.

Often, when a weed-carpeted pond shows a tint of
bright transparent green in autumn, a glass of the water,
dipped and held to the light, will be seen to be filled
with these rolling emerald spheres.

Euglena Several species of this genus (fig. 30^;) are
common inhabitants of slow streams and pools. They
are all most abundant in mid-summer, being apparently

attuned to high tempera-
tures. They are common
constituents of the water-
bloom that forms on the
surface of slow streams.
Figure I (p. 15) shows such
a situation, where they re-
cur every year i n J une . Cer-
tain of them are common in
pools at sewer outlets,
where bloodworms dwell in
the bottom mud. When
abundant in such places

FIG. 32. A Dinobryon colony.

they give to the water a
livid green color. Their
great abundance makes them important agents in
converting the soluble stuffs of the water into food
for rotifers and other microscopic animals.

Dinobryon This minute, amber-tinted flagellate
forms colonies on so unique a plan (fig. 30^) they are
not readily mistaken for anything else under the sun.
Each individual is enclosed in an ovoid conic case or
lorica, open at the front where two flagella protrude
(fig. 302') and many of them are united together in branch-
ing, a more or less tree-like colony. Since flagella

The Flagellates 107

always draw the body after them, these colonies swim
along with open ends forward, apparently in defiance
of all the laws of hydromechanics, rotating slowly on
the longitudinal axis of the colony as they go. Dino-
bryon is of an amber yellow tint, and often occurs in
such numbers as to lend the same tint to the water it
inhabits. It attains its maximum development at
low temperatures. In the cooler waters of our larger
lakes it is present in some numbers throughout the year,
though more abundant in winter. Kofoid reports it as
being "sharply limited to the period from November to
June" in Illinois River waters. Its sudden increase
there at times in the winter is well illustrated by the
pulse of 1899, when the numbers of individuals per
cubic meter of water in the Illinois River were on suc-
cessive dates as follows:

Jan. ioth, 1,500

Feb. 7th, 6,458,000

" i4th, 22,641,440

followed by a decline, with rising of the river.

Dinobryon often develops abundantly under the ice.
Its optimum temperature appears to be near o C. It
thus takes the place in the economy of the waters that
is filled during the summer by the smaller green

Synura (fig. 30^) is another winter flagellate, similar
in color and associated with Dinobryon, much larger
in size. Its cells are grouped in spherical colonies
united at the center of the sphere, and equipped on the
outer ends of each with a pair of flagella, which keep the
sphere in rolling locomotion. The colonies appear at
times of maximum development to be easily disrupted,

Online LibraryJames G. (James George) NeedhamThe life of inland waters; an elementary text book of fresh-water biology for students → online text (page 6 of 26)