James G. (James George) Needham.

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

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organization of nearly all of
them that indicates ancestral
adaptation to life on land.
They have more of hard parts,
more of localized feeding
organs, more of epidermal
specialization, and more dif-
erentiation of parts in the
body, than life in the water

They occupy merely the
margins of the water. A few
highly specialized genera,
well equipped for with-
standing partial or complete
submergence occupy the
shoals and these are backed Fl ?: 5 8 - The marsh mallow,

. -, -, -i . i Hibiscus Moscheutos.

on the shore line by a

mingled lot of semi-aquatics that are for the most part
but stray members of groups that abound on land.
Often they are single members of large groups and are
sufficiently distinguished from their fellows by a name
indicating the kind of wet place in which they grow.
Thus we know familiarly the floating riccia, the bog
mosses, the brook speedwell, the water fern and water
cress, the marsh bell flower and the marsh fern, the
swamp horsetail and the swamp iris, etc. All these


146 Aquatic Organisms

and many others are stragglers from large dry land
groups. That readaptation to aquatic life has occurred
many times independently is indicated by the fact that
the more truly aquatic families are small and highly
specialized, and are widely separated systematically.

Bryophytes Both liverworts and mosses are found
in our inland waters, though the former are but spar-
ingly represented. Two simple Riccias, half an inch long
when grown, are the liverworts most commonly found.
One, Ricciafluitans, grows in loose clusters of flat slender
forking sprays that drift about so freely that fragments
are often taken in pond and river plancton. The larger
unbroken more or less spherical masses of sprays are found
rolling with the waves upon the shores of muddy ponds.
The other, Ricciocarpus natans, has larger and thicker
sprays of green and purple hue, that float singly upon the
surface, or gather in floating masses covering considerable
areas of quiet water. They are not uncommonly found in
springtime about the edges of muddy ponds. Under-
neath the flat plant body there is a dense brush of
flattened scales.

Water mosses are more important. The most
remarkable of these are the bog mosses (Sphagnum).
These cover large areas of the earth's surface, especially
in northern regions, where they chiefly compose the
thick soft carpet of vegetation that overspreads open
bogs and coniferous swamps. They are of a light grey-
green color, often red or pink at the tips. These
mosses do not grow submerged, but they hold immense
quantities of water in their reservoir cells, and are able
to absorb water readily from a moist atmosphere ; so
they are always wet. Supported on a framework of
entangled root stocks of other higher plants, the bog
mosses extend out over the edges of ponds in floating
mats, which sink under one's weight beneath the water

Mossworts 147

level and rise again when the weight is removed. The
part of the mat which the sphagnum composes consists
of erect, closely-placed, unbranched stems, like those
shown in fig. 59, which grow ever upward at their tips,

FIG. 59. Bog moss, Sphagnum.

and die at the lower ends, contributing their remains
to the formation of beds of peat.

The leaves of Sphagnum are composed of a single layer
of cells that are of two very different sorts. There are
numerous ordinary narrow chlorophyl-bearing cells, and,
lying between these, there are larger perforate reservoir
cells, for holding water.


Aquatic Organisms

The true water mosses of the genus Fontinalis are
fine aquatic bryophytes. These are easily recognized,
being very dark in color and very slender. They grow
in spring brooks and in clear streams, and are often seen
in great dark masses trailing their wiry stems where the
current rushes between great boulders or leaps into
foam-flecked pools in mountain brooks.

Another slender brook-inhabiting moss is Fissidens
julianum, which somewhat resembles Fontinalis, but
which is at once distinguished by the deeply channeled

bases of its leaves, which
enfold the stem. The
leaves are two ranked and
alternate along the very
slender flexuous stem, and
appear to be set with edges
toward it.

There are also a few
lesser water mosses allied
to the familiar trailing
hypnums, so common in
deep woods. They grow
on stones in the bed of
brooks. They cover the
face of the ledges over
which the water pours in
floods and trickles in times of drouth, as with a fine
feathery carpet of verdure that adds much to the beauty
of the little waterfalls. They give shelter in such places
to an interesting population of amphibious animals, as
will be noted in chapter VI, following. The leaves of the
hypnums are rather short and broad, and in color they
are often very dark often almost black. *

*Grout has given a few hints for the recognition of these "Water-loving
hypnums" in his Mosses with a Hand Lens, 26. edition, p. 128. New York,

FIG. 60. Water mosses.

a, Fontinalis; b, Fissidens julianum, with a
single detached leaf, more enlarged; c,
Rhynchostegium rusciforme, with a single
detached leaf at the left. (After Grout.)



There are also a few hypnums found intermixed with
sphagnum on the surface of bogs, and as everyone
knows there are hosts of mosses in all moist places in
woods and by watersides.

FIG. 61. Two floating leaves of the "water shamrock," Marsilea, in the midst
of a surface layer of duck-meat (Spirodela polyrhiza). "Lemna" on fig. 62.

Pteridophytes Aquatic fernworts are few and of very
unusual types. There is at least one of them, how-
ever, that is locally dominant in our flora. Marsilea,
the so-called water shamrock or water fern, abounds on

Aquatic Organisms

the sunny shoals of muddy bayous about Ithaca and in
many places in New England. It covers the zone
between high and low water, creeping extensively over
the banks that are mostly exposed, and there forming
a most beautiful ground cover, while producing longer
leaf-stalks where submerged. These leaf -stalks carry
the beautiful four-parted leaf-blades to the surface
where they float gracefully. Fruiting bodies the size

**X* 1 '^s?


FIG. 62. Floating plants: The largest branching colonies are Azolla; the
smallest plants are Wolffia; those of intermediate size are Lemna minor.
Photo by Dr. Emmeline Moore.

of peas are produced in clusters on the creeping stems
above the water line, often in very great abundance.

Then there are two floating pteridophytes of much
interest. Salvinia, introduced from Europe, is found
locally along our northeastern coast, and in the waters
of our rich interior bottom lands the brilliant little
Azolla flourishes. Azolla floats in sheltered bogs
and back waters, intermingled with duckweeds. It is
reddish in color oftener than green and grows in minute
mosslike pinnately branched sprays, covered with

Aquatic Seed Plants 151

closely overlapping two-lobed leaves, and emits a few
rootlets from the under side which hang free in the
water. In the back waters about the Illinois Station at
Havana, Illinois, Azolla forms floating masses often
several feet in diameter, of bright red rosettes.

Shoreward there are numerous pteridophytes grow-
ing as rooted and emergent aquatics ; the almost grass-
like Isoetes, and the marsh horsetails and ferns, but
these latter differ little from their near relatives that
live on land.

Aquatic Seed Plants These are manifestly land
plants in origin. They have much stiffening in their
stems. They have a highly developed epidermal
system, often retaining stomates, although these can
be no longer of service for intake of air. They effect
fertilization by means of sperm nuclei and pollen tubes,
and not by free swimming sperm cells.

Seed plants crowd the shore line, but they rapidly
diminish in numbers in deepening water. They grow
thickest by the waterside because of the abundance of
air moisture and light there available. But too much
moisture excludes the air and fewer of them are able to
grow where the soil is always saturated. Still fewer
grow in standing water and only a very few can grow
wholly submerged. Moreover, it is only in protected
shoals that aquatic seed plants flourish. They cannot
withstand the beating of the waves on exposed shores.
Their bodies are too highly organized, with too great
differentiation of parts. Hence the vast expanses of
open waters are left in possession of the more simply
organized algae.

An examination of any local flora, such as that of
the Cayuga Lake Basin* will reveal at once how small a
part of the population is adapted for living in water.

*The following data are largely drawn from Dudley's Cayuga Flora, 1886.


Aquatic Organisms

In this area there are recorded as growing without
cultivation 1278 species. Of these 392 grow in the
water. However, fewer than forty species grow wholly
submerged, with ten or a dozen additional submerged
except for floating leaves. Hardly more than an eighth,

therefore, of the so-
called "aquatics" are
truly aquatic in mode
of life: the remaining
seven-eighths grow on
shores and in springs,
in swamps and bogs, in
ditches, pools, etc.,
where only their roots
are constantly wet.

The aquatic seed
plants are representa-
tive of a few small and
scattered families. In-
deed, the only genus
having any consider-
able number of truly
aquatic species is the
naiad genus Potamo-
geton. Other genera
of river- weeds, or true
pond weeds, are small,
scattered and highly
diversified. They bear
many earmarks of
the special situations

FIG. 63. The ruffled pond- weed; Pota-
mogeton crispus, one of the most orna-
mental of fresh water plants.

independent adaptation to

in the water which they severally occupy. In the
economy of nature the Potamogetons or river weeds
constitute the most important single group of sub-
merged seed plants. They are rooted to the bottom
in most shoal waters, and compose the greater part of

Aquatic Seed Plant? 153

the larger water meadows within our flora. They have
alternate leaves and slender flexuous sterns that are
often incrusted with lime.

There are evergreen species among the Potamogetons,
and other species that die down in late summer. There
are broad leaved and narrow leaved species. There
are a few, like the familiar Potamogeton natans whose
uppermost leaves float flat upon the surface, but
the more important members of the genus live wholly
submerged. Tho seed-plants, they mainly reproduce
vegetatively, by specialized reproductive buds that are
developed in the growing season, and are equipped with
stored starch and other food reserves, fitting them when
detached for rapid growth in new situations. These
reproductive parts are developed in some species as
tuberous thickenings of underground parts; in others
as burr-like clusters of thickened apical buds; and in
still others they are mere thickenings of detachable

The Potamogetons enter largely into the diet of wild
ducks and aquatic rodents and other lesser aquatic
herbivores. They are as important for forage in the
water as grasses are on land.

Other naiads are Nais (fig. 85) and Zannichellia.

Eel-grass (Vallisneria) is commonly mixed with the
pond weeds in lake borders and water meadows.
Eel -grass is apparently stemless and has long, flat,
flexuous, translucent, ribbonlike leaves, by which it
is easily recognized. The duckweeds (Lemnaceae, figs.
6 1 and 62) are peculiar free-floating forms in which the
plant body is a small flat thallus, that drifts about freely
on the surface in sheltered coves, mingled with such
liverworts as Ricciocarpus, with such fernworts as
Azolla, with seeds, eel-grass flowers, and other flotsam.
There are definite upper and lower surfaces to the thal-
lus with pendant roots beneath hanging free in the


Aquatic Organisms

water. Increase is by budding and outgrowth of new
lobes from pre-existing thalli. Flowering and seed
production are of rare occurrence.

Trie water lily
family includes
the more con-
spicuous of the
aquatics, which
pre-empt the
rich bottom mud
with stout root
stocks , and
heavily shade
the water with
large shield-
shaped leaves,
either floating
upon the sur-
face, as in the
water shield and
water lilies or
lifted somewhat
above it , as in the
spatterdock and
the lotus. They
are long-lived
perennials, re-
quiring a rich
muck soil to root
in. These are
for the beauty
and fragrance of
their flowers.

FIG. 64. Leaf -whorls.

A, and C, the hornwort (Ceratophyllum); B, the water milfoil
(Myriophyllum) . A is an old leaf, the upper half normally
covered with algae and silt; the lower half cleaned, save for a
closely adherent dwelling-tube of a midge larva in the fork at
the right. C, is a young partly expanded leaf whorl from the
apical bud.

Aquatic Seed Plants 155

The bladderworts (Utricularia) comprise another
peculiar group. They are free-floating, submerged
plants with long, flexuous branching stems that are
thickly clothed with dissected leaves. Attached to the
leaves are the curious traps or "bladders" (discussed in
Chapt. VI) which have suggested the group name.
Being unattached they frequent the still waters of
sheltered bays and ponds where they form beautiful
feathery masses of green. They shoot up stalks above
the surface bearing curious bilabiate flowers.

FIG. 65. The water weed, Philotria (Anacharis or Eloded), with
two young black-and-green-banded nymphs of the dragonfly Anax
on its stem, and a snail, Planorbis, on a leaf.

The horn wort (Ceratophyllum) is another non-rooting
water plant that grows wholly submerged and branch-
ing. It is coarser, however, and hardier than Utricu-
laria and much more widespread. Its leaves are stiff,
repeatedly forking, and spinous-tipped (fig. 64 A and C).

The water milfoils (Myriophylluni) are rooted aqua-
tics, superficially similar to the hornwort but dis-
tinguishable at a glance by the simple pinnate branch-
ing of the softer leaves (fig. 6^B).

Then there are a few very common aquatics that
form patches covering the beds of lesser ponds, bogs


Aquatic Organisms

and pools. The common water weed, Phil0tria, (fig. 65) ,
with its neat little leaves regularly arranged in whorls of
threes; and two water crowfoots, Ranunculus, (fig. 66),
white and yellow, with alternate finely dissected leaves ;
and the water purslane, Ludvigia palustris, with its
closely-crowded opposite ovate leaves are found here.
These are the common plants of the waterbeds about
Ithaca. They are so few one may learn them quickly,

for so strongly marked
are they that a single
spray or often a single
leaf is adequate for

Then there are three
small families so finely
adapted to withstand-
ing root submersion
that they dominate all
our permanent shoals
and marshes. These
are (i) the Typhaceae
including the cat-tails
and the bur-reeds,

FIG. 66. A leaf of the white water-crow- 1 . - r 1

foot, Ranunculus. which f orm vast stretch-

es of nearly clear

growth, as discussed in the last chapter; (2) the Alis-
maceae, including arrow heads and water plantain, and
(3) the Pontederiaceae, represented by the beautiful blue
pickerel-weed. All these are shown in their native
haunts in the figures of chapter VI.

Another family of restricted aquatic habitat is the
Droseraceae, the sun-dews, which grow in the borders of
sphagnous upland bogs. They are minute purplish-
tinted plants whose leaves bear glandular hairs.

Few other families are represented in the water by
more than a small proportion of their species. Those

Aquatic Seed Plants


families are best represented whose members live
chiefly on low grounds and in moist soil. A few rushes
(Juncaceae) invade the water on wave-washed shores
at fore front of the standing aquatics. A few sedges

FIG. 67. Fruit clusters of four emergent aquatic seed
plants; arrow-arum (Peltandra) , pickerel- weed (Pon-
tederia), burr-reed (Sparganium), and sweet flag
(A corns).

(Carices) overrun flood-plains or fringe the borders of
ditches. A very few grasses preempt the beds of
shallow and impermanent pools. A few aroids, such
as arrow arum and the calla adorn the boggy shores.
A few heaths, such as, Cassandra and Andromeda over-
spread the surface of upland sphagnum bogs with dense


Aquatic Organisms

levels of shrubs, and numerous orchids occupy the sur-
face of the bog beneath and between the shrubs.
Willows and alders fringe all the streams, associated
there with a host of representatives of other families
crowding down to the waterside. A few of these on
account of their usefulness or their beauty, we shall
have occasion to consider in a subsequent chapter.

Such are the dominant aquatic seed plants in the
Cayuga Basin; and very similar are they over the
greater part of the earth. The semi-aquatic represen-
tatives of the larger families are few and differ little
from their terrestrial relatives: the truly aquatic
families are small and highly diversified.

plants, so with animals, it
are predominantly aquatic,
are the protozoans ; so with


ANY of the lower groups of
animals are wholly aqua-
tic, never having de-
parted from their ances-
tral abode. Other groups
are in part adapted to
life on land. A few
others, after becoming fit
for terrestrial life, have
been readapted in part to
life in the water. Aqua-
tic insects and mammals,
especially, give evidence
of descent from terres-
trial ancestors. As with

is the lower groups that
The simplest of animals

these we will begin.



Protozoans One of the best known animals in the
world, one that is pedagogically exploited in every
biological laboratory, is the Amoeba, (fig. 690). Plastic,
ever changing in form and undifferentiated in parts,
this is the animal that is the standard of comparison
among things primitive. Its name
has become a household word, and an
every -day figure of speech. A little
living one-celled mass of naked pro-
toplasm, that creeps freely about
amid the ooze of the pond bottom,
and feeds on organic foods. It
grows just large enough to be recog-
nized by the naked eye when in most
favorable light, as when creeping up
the side of a culture jar: on the
pond bottom it is undiscoverable
and a microscope is essential to
study it.

Related to Amoeba are several
common shell-bearing forms of the
group of Sarcodina (Rhizopoda)
that often become locally abun-
dant. Difflugia (fig. 6gc) forms a
flask-shaped shell composed of mi-
nute granules, that, magnified, look
like grains of sand stuck together
over the outside. The soft amceba-like body protrudes
in pseudopodia from the mouth of the flask, when travel-
ing or foraging, or withdraws inside when disturbed.
Arcella (fig. 696) secretes a broadly domeshaped shell,
having a concave bottom, in the center of which is the
hole whence dangle the clumsy pseudopodia. One
species of Arcella, shown in the following figure, has
the margin of the shell strongly toothed. Both of
these genera, and other shell-bearing forms, secrete

FIG. 69. Protozoans.
a, Amoeba; b, Arcella; c


Aquatic Organisms

FIG. 70. Arcella dentata.
Through the central opening
there is seen a diatom, re-
cently swallowed.

bubbles of gas within their
shells whereby they are caused
^^^^^ to float. Thus they are often

j^ taken in the plancton net from

|O mf open water of the ponds and


H^ Other protozoans that have

the body more or less cov-
ered with vibratile cilia (Cil-
iata), are very common in
freshwater, especially in ponds
and pools. Best known of
these is Paramecium, (fig.
7 1 a) another familiar biolog-
ical-laboratory "type" that

grows abundantly in plant infusions. It is found in

stagnant pools, swimming near the surface. There

are many species of Paramecium. Some of them and

some members of allied genera are characteristic of

polluted waters. Other allied genera are parasitic,

and live within the bodies of the

higher animals. Stentor is (as the

name signifies) a more or less

trumpet-shaped ciliate protozoan,

that may detach itself and swim

freely about, but that is ordi-
narily attached by its slender

base to some support. Its base

is in some species surrounded by

a soft gelatinous transparent

lorica, as shown in the figure.

Some species are of a greenish

color. Stentor and Paramecium,

tho unicellular, are quite large

enough to be seen (as moving

specks) with the unaided eye.

FIG. 71. Ciliate pro-

A, Paramoscium; n, nu-
cleus; v, v, vacuoles; /,
food-ball at the bottom of
the rudimentary esopha-
gus; C, Stentor; I, lorica.

Protozoans 161

Cothurnia (fig. 73^:) is a curious double form that is
often found attached to the stems of water weeds. The
two cells of unequal height are surrounded by a thin
transparent lorica. For beauty of form and delicacy or
organization it would be hard to find anything surpas-
sing this little creature.

Vorticella and its allies are among the commonest
and most ubiquitous of protozoans. They are sessile
and stalked, with some portion or all of the base con-
tractile. Vorticella forms clusters of many separate
individuals, while Epistylis forms branching, tree-like
compound colonies (fig. 72). Oftentimes they com-
pletely clothe twigs and grass stems
lying in the water, as with a white
fringe. Often they cluster about the
appendages of crustaceans and insects,
or thickly clothe their shells. Some-
times they cling to floating algal fila-
ments in the water-bloom (see fig. 179
on p. 295).

Ophrydium forms colonies of a very-
different sort. Numerous weak-stalked
individuals have their bases imbedded
in a roundish mass of gelatin. The FlG>72 Acolonyof
colonies lie scattered about over the

bottom of a lake or pond. They are The dark object on the

... - fl c , 1 Slde f the stalk is an

roundish, or often rather shapeless e gg , probably the e gg of

- a rotifier.

masses varying in size from mere specks
up to the dimensions of a hen's egg. In the summer of
1906 the marl-strewn shoals of Walnut Lake in Michigan
were so thickly covered that a boat-load of the soft
greenish-white colonies could easily have been gathered
from a small area of the bottom.

Other forms of protozoa there are in endless variety.
We cannot even name the common ones here: but we
will mention two that are very different from the fore-

1 62

Aquatic Organisms

going in form and habit. Podophrya will of ten be encoun-
tered by searching the backs of aquatic insects or the
sides of submerged twigs, or other solid support, to which
it is attached. It is sessile, and reaches out its suctorial
pseudopodia in search of soft-bodied organisms that are
its prey.

Anthophysa is a curious sessile form that is common
in polluted waters. It forms very minute spherical
colonies that are attached to the transparent tip of a

FIG. 73. Three sessile protozoans.

A, Anthophysa; B, Podophrya; C, Cothurnia.

rather thick brownish stalk. The stalk increases in
length and diameter with age, occasionally forking when
the colony divides. It soon becomes much more con-
spicuous than the colonies it carries. It often persists
after the animals are dead and gone. After a vigorous
growth, the accumulated stalks sometimes cover every
solid support as with a soft flocculent brownish fringe.
Besides these and other free-living forms, there are
parasitic Protozoa whose spores get into the water.
Some of these are pathogenic; many of them have
changes of host; all of them are biologically interesting;
but we have not space for their consideration here.
We must content ourselves with the above brief
mention of a few of the more common and interesting
free-living forms.

Aquatic Organisms 163


Hydras are the only common fresh-water representa-
tives of the great group of Coelenterates, so abundant
in the seas; and of hydras there are but a few species.
Two of these, the common green and brown ones,
H. virdis and H. fusca, are well enough known, being
among the staples of every biological laboratory.
Pedagogically it is a matter of great good fortune that
this little creature lives on, a common denizen of fresh-
water pools; for its two-layered sac-like body repre-
sents well the simplest existing type of metazoan

Hydras are ordinarily sessile, being attached by a

Online LibraryJames G. (James George) NeedhamThe life of inland waters; an elementary text book of fresh-water biology for students → online text (page 9 of 26)