filaments in some species, and in one, extends outward
in long picturesque sprays, but which has in all much
the same form of plant body (fig. 48) a close-set branch-
ing filament, with the tips of some of the branches ending
in a long hyaline bristle-like point. Chaetophora grows
very abundantly in stagnant pools and ponds in mid-
summer, adhering to every solid support that offers,
and it is an important part of the summer food of many
of the lesser herbivores in such waters.
Then we must not omit to mention two that, if less
important, are certainly no less interesting: Drapar-
naldia (fig. 45^) which lets its exceedingly delicate sprays
trail like tresses among the submerged stones in spring-
FIG. 49. Coleochate scutata. "Green doily."
fed rivulets; and Coleochczte (fig. 49), which spreads its
flattened branches out in one plane, joined by their
edges, forming a disc, that is oftenest found attached to
the vertical stem of some reed or bulrush.
Miscellaneous lesser green alga Among other green
algae, which are very numerous, we have space here for
a mere mention of a few of the forms most likely to be
met with, especially by one using a plancton net in open
waters. These will also illustrate something of the
Lesser Green Algae
remarkable diversity of form and of cell grouping among
the lesser green algae.
Botryococcus grows in free floating single or compound
clusters of little globose green cells, held together in a
scanty gelatinous investment. The clusters are suffi-
ciently grape-like to have suggested the scientific name
They contain, when grown, usually 1 6 or 32 cells each.
They are found in the open waters of bog pools, lakes,
FIG. 50. Miscellaneous green algae (mostly after West).
a, Botryococcus; b, Ccelastrum; c, Dictosphesrium; d, Kirchnftrella;
e, Selenastrum; /, Ankistrodesmus falcatus; g, Ophiocytium; /,
Tetraspora; i, Crucigenia; j, Scenedesmus;, k, Rhicteriella; I,
Ankislrodesmus setigerus; m, Oocystis.
and streams, during the warmer part of the season,
being most abundant during the hot days of August.
When over-abundant the cells sometimes become filled
with a brick-red oil. They occur sparingly in water-
Dictyosphcerum likewise grows in more or less spheri-
cal colonies of globose cells. The cells are connected
together by dichotomously branching threads and all
are enveloped in a thin spherical mass of mucus. The
colonies are free floating and are taken in the plancton of
ponds and lakes and often occur in the water-bloom.
130 Aquatic Organisms
Ccelastrum is another midsummer plancton alga that
forms spherical colonies of from 8 to 32 cells ; it has much
firmer and thicker cell walls, and the cells are often
angulate or polyhedral. New colonies are formed within
the walls of each of the cells of the parent colony, and
when well grown these escape by rupture or dissolution
of the old cell wall. Our figure shows merely the out-
line of the cell walls of a i6-celled colony, in a species
having angulate cells, between which are open inter-
spaces. Kofoid found Ccelastrum occurring in a maxi-
mum of 10,800,000 per cubic meter of water in the
Illinois River in August.
Crucigenia is an allied form having ovoid or globose
cells arranged in a flat plate held together by a thin
mucilaginous envelope. The cells are grouped in fours,
but 8, 1 6, 32, 64 or even more may, when undisturbed,
remain together in a single flat colony. During the
warmer part of the season, they are common constit-
uents of the fresh-water plancton, the maximum heat
of midsummer apparently being most favorable to their
Scenedesmus is a very hardy, minute, green alga of
wide distribution. There is hardly any alga that
appears more commonly in jars of water left standing
about the laboratory. When the sides of the jar begin
to show a film of light yellowish-green, Scenedesmus
may be looked for. The cells are more or less spindle-
shaped, sharply pointed, or even bristle-tipped at the
ends. They are arranged side by side in loose flat rafts
of 2, 4 or 8 (oftenest, when not broken asunder, of 4)
cells. They are common in plancton generally, espec-
ially in the plancton of stagnant water and in that of
polluted streams, and although present at all seasons,
they are far more abundant in mid and late summer.
Lesser Green Algae 131
Kirchnerella is a loose aggregate of a few blunt-
pointed U-shaped cells, enveloped in a thick spherical
mass of jelly. It is met with commonly in the plancton
of larger lakes. Selenastrum grows in nearly naked
clusters of more crescentic, more pointed cells which are
found amid shore vegetation. Ankistrodesmus is a
related, more slender, less crescentic form of more
extensive littoral distribution. The slenderest forms of
this genus are free floating, and some of them like A.
setigera (fig. 50 /) are met with only in the plancton.
Richteriella is another plancton alga found in free
floating masses of a few loosely aggregated cells. The
cells are globose and each bears a few long bristles upon
its outer face. Kofoid found Richteriella attaining a
maximum of 36,000,000 per cubic meter of water in
September, while disappearing entirely at temperatures
below 60 F.
Oocystis grows amid shore vegetation, or the lighter
species, in plancton in open water. The ellipsoid cells
exist singly, or a few are loosely associated together in a
clump of mucus. The cells possess a firm smooth wall
which commonly shows a nodular thickening at each
Ophiocytium is a curious form with spirally coiled
multinucleate cells. The bluntly rounded ends of the
cells are sometimes spine-tipped. These cells some-
times float free, sometimes are attached singly, some-
times in colonies. Kofoid found them of variable
occurrence in the Illinois River, where the maximum
number noted was 57,000,000 per cubic meter occur-
ring in September. The optimum temperature, as
attested by the numbers developing, appeared to be
about 60 F.
Tetraspora We will conclude this list of miscellanies
with citing one that grows in thick convoluted strings
132 Aquatic Organisms
and loose ropy masses of gelatin of considerable size.
These masses are often large enough to be recognized
with the unaided eye as they lie outspread or hang down
upon trash on the shores of shoal and stagnant waters.
Within the gelatin are minute spherical bright green
cells, scattered or arranged in groups of fours.
BLUE-GREEN ALG^E (Cyanophycecz or M yxophycece) .
The "blue-greens" are mainly freshwater algae, of simple
forms. The cells exist singly, or embedded together in
loose gelatinous envelope or adhere in flat rafts or in
filaments. Their chlorophyl is rather uniformly dis-
tributed over the outer part of the cell (quite lacking the
restriction to specialized chloroplasts seen in the true
green-algae) and its color is much modified by the
presence of pigment (phycocyanin) , which gives to the
cell usually a pronounced bluish-green, sometimes, a
Blue-green algae exist wherever there is even a little
transient moisture on tree trunks, on the soil, in
lichens, etc. ; and in all fresh water they play an impor-
tant role, for they are fitted to all sorts of aquatic
situations, and they are possessed of enormous reproduc-
tive capacity. Among the most abundant plants in the
water world are the Anabcznas (fig. 1 79) , and other blue-
greens that multiply and fill the waters of our lakes in
midsummer, and break in "water-bloom" covering the
entire surface and drifting with high winds in windrows
on shore. Such forms by their decay often give to the
water of reservoirs disagreeable odors and bad flavors,
and so they are counted noxious to water supplies.
There are many common blue-greens, and here we
have space to mention but a few of the more common
forms. Two of the loosely colonial forms composed of
spherical cells held together in masses of mucus are
Ccelosphczrium and Microcystis. Both these are often
associated with Anabaena in the water-bloom. Coelos-
phserium is a spherical hollow colony of microscopic size.
It is a loose association of cells, any of which on separa-
tion is capable of dividing and producing a new colony.
Microcystis (fig. 51 A) is a mass of smaller cells, a very
loose colony that is at first more or less spherical but
later becomes irregularly lobed and branching. Such
old colonies are often large enough to be observed with
the naked eye. They are found most commonly in late
summer, being hot
weather forms. When
abundant these two are
often tossed by the
waves upon rocks along
the water's edge, and
from them the dirty blue-
green deposit that is
popularly known as
1 'green paint."
Among the members
of this group most com-
monly seen are the motile
blue-greens of the genus
FIG. 51. Miscellaneous blue-green
algae (mostly after West).
A, Microcystis (Clathrocystis) ; B, C, D,
Tetrapedia; E, Spirulina; F, Nostoc; G,
Oscillatoria; H, Rivularia.
These grow in dense, strongly colored tufts and patches
of exceedingly slender filaments attached to the bottoms
and sides of watering troughs, ditches and pools,
and on the beds of ponds however stagnant. They
thickly cover patches of the black mud bottom
and the formation of gases beneath them disrupts their
attachment and the broken flakes of bottom slime that
they hold together, rise to the surface and float there,
much to the hurt of the appearance of the water.
The filaments of Oscillatoria and of a few of its near
allies perform curious oscillating and gliding movements.
Detached filaments float freely in the open water, and
134 Aquatic Organisms
during the warmer portion of the year, are among the
commoner constituents of the plancton.
There are a number of filamentous blue-greens that
are more permanently sessile, and whose colonies of
filaments assume more definite form. Rivularia is
typical of these. Rivularia grows in hemispherical
gelatinous lumps, attached to the leaves and stems of
submerged seed plants. In autumn it often fairly
smothers the beds of hornwort (Ceratophyllum) and
water fern (Marsilea) in rich shoals. Rivularia is
FIG. 52. Colonies of Rivularia on a disintegrating
brownish in color, appearing dirty yellowish under the
microscope. Its tapering filaments are closely massed
together in the center of the rather solid gelatinous
lump. The differentiation of cells in the single filament
is shown in fig. 51 H. Such filaments are placed side
by side, their basal heterocysts close together, their tips
diverging. As the mass grows to a size larger than a pea
it becomes softer in consistency, more loosely attached
to its support and hollow. Strikingly different in form
and habits is the raftlike Merismopcedia (fig. 53). It
is a flat colony of shining blue-green cells that divide in
two planes at right angles to each other, with striking
Red and Brown Algae 135
regularity. These rafts of cells drift about freely in
open water, and are often taken in the plancton, though
rarely in great abundance. They settle betimes on the
leaves of the larger water plants, and may be discovered
with a pocket lens by searching the sediment shaken
FIG. 53. Merismopaedia.
RED and BROWN ALG.E (Rhodophycece andPhceophycea)
These groups are almost exclusively marine. A few
scattering forms that grow in fresh water are shown in
figure 54. Lemanea is a torrent -inhabiting form that
grows in blackish green tufts of slender filaments,
attached to the rocks in deep clear mountain streams
where the force of the water is greatest. It is easily
recognizable by the swollen or nodulose appearance of
the ultimate (fruiting) branches. Chantransia is a
beautiful purplish-brown, extensively branching form
that is more widely distributed. It is common in clear
flowing streams . It much resembles Cladophora in man-
ner of growth but is at once distinguished by its color.
FIG. 54. Red and brown algae (after West).
a, Lemanea; b, Chantransia; c, Batrachospermum; d, Hydrurus.
Batrachospermum is a freshwater form of wide distri-
bution, with a preference for spring brooks, though occur-
ring in any water that is not stagnant. It grows in
branching filaments often several inches long, enveloped
in a thick coat of soft transparent mucus. The color is
bluish or yellowish-green, dirty yellow or brownish.
Attached to some stick or stone in a rivulet its sprays, of
more than frond-like delicacy, float freely in the water.
Hydrurus grows in branched colonies embedded in a
tough mucilage, attached to rocks in cold mountain
streams. The colonies are often several inches long.
Their color is olive green. They have a plumose
appearance, and are of very graceful outline.
The stoneworts (Characece). This group is well repre-
sented in freshwater by two common genera, well known
to every biological laboratory student, Char a and
Nitella. Both grow in protected shoals, and in the
borders of clear lakes at depths below the heavy beating
of the waves. Both are brittle and cannot withstand
FIG. 55. Nitella glomerulifera.
wave action. Both prefer the waters that flow off from
calcareous soils, and are oftenest found attached to a
The stoneworts, are the most specialized of the fresh-
water algae: indeed, they are not ranked as algae by
some botanists. In form they have more likeness to
certain land plants than to any of the other algae.
138 Aquatic Organisms
They grow attached to the soil. They grow to consider-
able size, often a foot or more in length of stern. They
grow by apical buds, and they send out branches in
regular whorls, which branch and branch again, giving
the plant as a whole a bushy form. The perfect regu-
larity of the whorled branches and the brilliant colora-
tion of the little spermaries borne thereon, doubtless
have suggested the German name for them of " Cande-
The stoneworts are so unique in structure and in repro-
ductive parts that they are easily distinguished from
other plants. The stems are made up of nodes and
internodes. The nodes are made up of short cells from
which the branches arise. The internodes are made up
of long cells (sometimes an inch or more long), the
central one of which reaches from one node to another.
In Nitella there is a single naked internodal cell com-
posing entirely that portion of the stem. In Chara this
axial cell is covered externally by a single layer of
slenderer cortical cells wound spirally about the central
one. A glance with a pocket lens will determine whether
there is a cortical layer covering the axial internodal
cell, and so will distinguish Chara from Nitella. Chara
is usually much more heavily incrusted with lime in our
commoner species, and in one very common one, Chara
fcetida, exhales a bad odor of sulphurous compounds.
The sex organs are borne at the bases of branchlets.
There is a single egg in each ovary, charged with a rich
store of food products, and covered by a spirally wound
cortical layer of protecting cells. These, when the egg
is fertilized form a hard shell which, like the coats of a
seed, resist unfavorable influences for a long time.
This fruit ripens and falls from the stem. It drifts
about over the bottom, and later it germinates.
At the apex of the ovary is a little crown of cells,
between which lies the passageway for the entrance of
Chlorophylless Plants 139
the sperm cell at the time of fertilization. This crown
is composed of five cells in Chara ; of ten cells in Nitella.
It is deciduous in Chara; it is persistent in Nitella.
The stoneworts, unlike many other algae, are wonder-
fully constant in their localities and distribution, and
regular in their season of fruiting. They cover the
same hard bottoms with the same sort of gray-green
meadows, year after year, and although little eaten by
aquatic animals, they contribute important shelter for
them, and they furnish admirable support for many
CHLOROPHYLLESS WATER PLANTS, BACTERIA
Nature's great agencies for the dissolution of dead
organic materials, in water as on land, are the plants
that lack chlorophyl. They mostly reproduce by
means of spores that are excessively minute and abund-
ant, and that are distributed by wind or water every-
where; consequently they are the most ubiquitous of
organisms. They consume oxygen and give off carbon
dioxide as do the animals, and having no means of
obtaining carbon from the air, must get it from car-
bonaceous organic products usually from some carbo-
hydrate, like sugar, starch, or cellulose. Some of them
can utilize the nitrogen supply of the atmosphere but
most of them must get nitrogen also from the decompo-
sition products of pre-existing proteins. Many of them
produce active ferments, which expedite enormously the
dissolution of the bodies of dead plants and animals.
Some bacteria live without free oxygen.
It follows from the nature of their foods, that we find
these chlorophylless plants abounding where there is the
best supply of organic food stuffs: stagnant pools
filled with organic remains, and sewers laden with the
140 Aquatic Organisms
city's waste. But there is no natural water free from
them. Let a dead fly fall upon the surface of a tumbler
of pond water and remain there for a day or two and it
becomes white with water mold, whose spores were
present in the water. Let any organic solution stand
exposed and quickly the evidence of rapid decomposition
appears in it. Even the dilute solutions contained in a
laboratory aquarium, holding no organic material other
than a few dead leaves will often times acquire a faint
purple or roseate hue as chromogenic bacteria multiply
Bacteria A handful of hay in water will in a few
hours make an infusion, on the surface of which a film
of "bacterial jelly" will gather. If a bit of this "jelly"
be mounted for the microscope, the bacteria that secrete
it may be found immersed in it, and other bacteria
will be found adherent to it. All the common form-
types, bacillus, coccus and spirillum are likely to be seen
readily. Thus easy is it to encourage a rich growth of
water bacteria. Among the bacteria of the water are
numerous species that remain there constantly (often
called "natural water bacteria"), commingled at certain
times and places with other bacteria washed in from the
surface of the soil, or poured in with sewage. From the
last named source come the species injurious to human
health. These survive in the open water for but a short
time. The natural water bacteria are mainly beneficial ;
they assist in keeping the world's food supply in circula-
tion. Certain of them begin the work of altering the
complex organic substances. They attack the proteins
and produce from them ammonia and various ammonia-
cal compounds. Then other bacteria, the so-called
"nitrifying" bacteria attack the ammonia, changing it
to simpler compounds. Two kinds of bacteria succes-
sively participate in this: one kind oxidizes the
ammonia to nitrites; a second kind oxidizes the
nitrites to nitrates. By these successive operations the
stores of nitrogen that are gathered together within the
living bodies of plants and animals are again released
for further use. The simple nitrates are proper food
for the green algae, with whose growth the cycle begins
again. And those bacteria which promote the pro-
cesses of putrefaction, are thus the world's chief agen-
cies for maintaining undiminished growth in perpetual
Bacteria are among the smallest of organisms. Little
of bodily structure is discoverable in them even with
high powers of the microscope, and consequently they
are studied almost entirely in specially prepared cul-
tures, made by methods that require the technical
training of the bacteriological laboratory for their
mastery. Any one can find bacteria in the water, but
only a trained specialist can tell what sort of bacteria
he has found; whether pathogenic species like the
typhoid bacillus, or the cholera spirillum; or whether
harmless species, normal to pure water.
The higher bacteria Allied to those bacilli that grow
in filaments are some forms of larger growth, known as
Trichobacteria, whose filaments sometimes grow
attached in colonies, and in some are free and motile.
A few of those that are of interest and importance in
fresh-water will be briefly mentioned and illustrated
Leptothrix* (Fig. 56^, b and c) grows in tufts of slender,
hairlike filaments composed of cylindric cells sur-
rounded by a thin gelatinous sheath. In reproduction
the cells are transformed directly into spores (gonidia)
which escape from the end of the sheath and, finding
favoring conditions, grow up into new filaments.
*Known also as Streptothrix and Chlamydothrix.
Crenothrix (Fig. 56 d, e and/) is a similar unbranched
sessile form which is distinguished by a widening of the
filaments toward the free end. This is caused by a
division of the cells in two or three planes within the
sheath of the filament, previous to spore formation.
Often by the germination of spores that have settled
upon the outside of the old sheaths and growth of new
filaments therefrom compound masses of appreciable
FIG. 56. Trichobacteria.
a, b, c, Leptpthrix (Streptothrix, or Chlamydothrix) . a, a colony; b, a single filament; c, spore
formation; d, e, /, Crenothrix; d, a single growing filament; e, a fruiting filament; /, a
compound colony; g, Cladothrix, a branching filament; h, Beggiatoa, younger and older
filaments, the latter showing sulphur granules, and no septa between cells of the filament.
size are produced. In the sheaths of the filaments a
hydroxide of iron is deposited (for Crenothrix possesses
the power of oxidizing certain forms of iron) ; and with
continued growth the deposits sometimes become
sufficient to make trouble in city water supply systems
by stoppage of the pipes. In nature, also, certain
deposits of iron are due to this and allied forms properly
known as iron bacteria. Cladothrix (Fig. 56 g), is a
related form that exhibits a peculiar type of branching
in its slender cylindric filaments.
Beggiatoa (fig. 56 ti) is the commonest of the so-called
sulfur bacteria. Its cylindric unbranched and unat-
tached filaments are motile, and rotate on the long axis
with swinging of the free ends. The boundaries be-
tween the short cylindric cells are often obscure,
especially when (as is often the case) the cells are filled
with highly refractive granules of sulfur. Considerable
deposits of sulfur, especially about springs, are due to
the activities of this and allied forms.
Water molds True fungi of a larger growth abound
in all fresh waters, feeding on almost every sort of
organic substance contained
therein. The commonest of
the water molds are the Sap-
rolegnias, that so quickly
overgrow any bit of dead
animal tissue which may
chance to fall upon the sur-
face of the water and float
there. If it be a fly, in a
day or two its body is sur-
rounded by a white fringe of
radiating fungus filaments,
outgrowing from the body.
The tips of many of these
filaments terminate in cylin-
dric sporangia, which when
FIG. 57. A common water mold,
Saprolegnia. (After Engler and
mature, liberate from their ruptured tips innumerable
biciliated free-swimming swarm spores. These wander
in search of new floating carcases, or other suitable food.
Certain of these water molds attack living fishes,
entering their skin wherever there is a a slight abrasion
of the surface, and rapidly producing diseased condi-
tions. These are among the worst pests with which the
fish culturist has to contend. They attack also the
144 Aquatic Organisms
eggs of fishes during their incubation, as shown in a
figure in a later chapter.
Most water molds live upon other plants. Even the
Saprolegnias have their own lesser mold parasites.
Many living algae, even the lesser forms like desmids
and diatoms are subject to their attack. Fine cultures
of such algae are sometimes run through with an
epidemic of mould parasites and ruined.
(Mossworts, Fernworts and Seed Plants)
In striking contrast with the algae, the higher plants
live mainly on land, and the aquatics among them
are restricted in distribution to shoal waters and to
the vicinity of shores. There is much in the bodily