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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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and single cells and small clusters of cells are often found
along with well formed colonies. Synura when abund-
ant often gives to reservoir waters an odor of cucumbers,



io8



Aquatic Organisms



and a singularly persistent bad flavor, and under such
circumstances it becomes a pest in water supplies.

Glenodinium (fig. 3O/), Peridinium, and Ceratium
(fig. 307) are three brownish shell-bearing flagellates of
wide distribution often locally abundant, especially in
spring and summer. These all have one of the two long
flagella laid in a transverse groove encircling the body,

the other flagellum free (fig. 33).
Glenodinium is the smallest,
Ceratium, much the largest.
Glenodinium has a smooth
shell, save for the grooves where
the flagella arise. Peridinium
has a brownish chitinous shell,
divided into finely reticulate
plates. Ceratium has a heavy
grayish shell prolonged into
several horns.

On several occasions in spring
we have seen the waters of the
Gym Pond on the Campus at
Lake Forest College as brown
as strong tea with a nearly pure
culture of Peridinium and con-
currently therewith we have
seen the transparent phantom-larvae of the midge
Corethra in the same pond all showing a conspicuous
brown line where the alimentary canal runs through
the body, this being packed full of Peridinia.

Trachelomonas (fig. 30 d) is a spherical flagellate hav-
ing a brownish shell with a short flask-like neck at one
side whence issues a single flagellum. This we have
found abundantly in pools that were rich in oak leaf
infusions.



FIG. 33. Ceratium (The trans-
verse groove shows plainly,
but neither flagellum shows
in the photograph.)



Diatoms



log



Diatoms Diatoms are among the most abundant of
living things in all the waters of the earth. They occur
singly and free, or attached by gelatinous stalks, or




FIG. 34. Miscellaneous diatoms, mostly species of Navicula; the filaments
are blue-green algae, mostly Oscillatoria.

aggregated together in gelatinous tubes, or compactly
grouped in more or less coherent filaments. All are
of microscopic size. They are most easily recognized by
their possession of a box-like shell, composed of two
valves, with overlapping edges. These valves are
stiffened by silica which is deposited in their outer walls,
often in beautiful patterns. The opposed edges of the



no Aquatic Organisms

valves are connected by a membraneous portion of the
cell wall known as the girdle. A diatom may appear
very different viewed from the face of the valve, or from
the girdle (see fig. 35^ and b, or j and k). They are
circular-like pill-boxes in one great group, and more or
less elongate and bilateral in the others.

Diatoms are rarely green in color. The chlorophyll
in them is suffused by a peculiar yellowish pigment
known as diatomin, and their masses present tints of
amber, of ochre, or of brown ; sometimes in masses they
appear almost black. The shells are colorless; and,
being composed of nearly pure silica, they are well
nigh indestructible. They are found abundantly in
guano, having passed successively through the stomachs
of marine invertebrates that have been eaten by fishes,
that have been eaten by the birds responsible for the
guano deposits, and having repeatedly resisted diges-
tion and all the weathering and other corroding effects
of time. They abound as fossils. Vast deposits of
them compose the diatomaceous earths. A well-known
bed at Richmond, Va., is thirty feet in thickness and of
vast extent. Certain more recently discovered beds
in the Rocky Mountains attain a depth of 300 feet.
Ehrenberg estimated that such a deposit at Biln in
Bohemia contained 40,000,000 diatom shells per cubic
inch.

Singly they are insignificant, but collectively they are
very important, by reason of their rapid rate of increase,
and their ability to grow in all waters and at all ordinary
temperatures. Among the primary food gatherers
of the water world there is no group of greater import-
ance.

In figure 35 we present more or less diagrammatically
a few of the commoner forms. The boat-shaped, freely
moving cells of Navicula (a, b, c) are found in every
pool. One can scarcely mount a tuft of algae, a leaf



Diatoms



in



of water moss or a drop of sediment from the bottom
without finding Naviculas in the mount. They are
more abundant shoreward than in the open waters of
the lake. The "white-cross diatom" Stauroneis (d), is a
kindred form, easily recognizable by the smooth cross-
band which replaces the middle nodule of Navicula.




FIG. 35. Diatoms.

a, valve view showing middle and end nodules, and b, girdle view of Navicula. c, another
species of Navicula; d, Stauroneis; e, valve view and /, girdle view of Tabellaria; g,
Synedra; h, Gyrosigma; i, a gelatinous cord-like cluster of Encyonema showing girdle
view of nine individuals and valve view of three, j, valve view and k, girdle view of
Melosira; l,Stephanodiscus; tn, Meridian colony, with a single detached individual shown
in valve view below; n, a small colony of Asterionella; o, valve view, and p, girdle view
of Camplylodiscus; q, cluster of Cocconema. (Figures mostly after Wolle).

Tabellaria (e and /) is a thin flat-celled diatom that
forms ribbon-like bands, the cells being apposed, valve
to valve. Often the ribbons are broken into rectangu-
lar blocks of cells which hang together in zig-zag lines
by the corners of the rectangles. The single cell is long-
rectangular in girdle view (slightly swollen in the middle
and at each end, as shown at e, in valve view), and is
traversed by two or more intermediate septa. Tabel-
laria abounds in the cool waters of our deeper northern
lakes, at all seasons of the year. It is much less common
in streams.



H2 Aquatic Organisms

The slender cells of the" needle diatoms," Synedra (g),
are common in nearly all waters and at all seasons.
They are perhaps most conspicuously abundant when
found, as often happens, covering the branches of some
tufted algae, such as Cladophora, in loose tufts and
fascicles, all attached by one end.

Gyrosigma (ti) is nearly allied to Navicula but is
easily recognized by the gracefully curved outlines of its
more or less S-shaped shell. The sculpturing of this
shell (not shown in the figure) is so fine it has long been a
classic test-object for the resolving power of microscopic
lenses. Gyrosigma is a littoral associate of Navicula,
but of much less frequent occurrence.

Encyonema (i) is noteworthy for its habit of develop-
ing in long unbranched gelatinous tubes. Sometimes
these tubes trail from stones on the bottom in swift
streams. Sometimes they radiate like delicate filmy
hairs from the surfaces of submerged twigs in still
water. The tubes of midge larvae shown in figure 134
were encircled by long hyaline fringes of Encyonema
filaments, which constituted the chief forage of the
larvae in the tubes and which were regrown rapidly
after successive grazings. When old, the cells escape
from the gelatine and are found singly.

The group of diatoms having circular shells with
radially arranged sculpturing upon the valves is repre-
sented by Melosira (j and k) and Stephanodiscus (I) of
our figure. Melosira forms cylindric filaments, whose
constituent cells are more solidly coherent than in
other diatoms. Transverse division of the cells in-
creases the length of the filaments, but they break with
the movement of the water into short lengths of usually
about half a dozen cells. They are common in the
open water of lakes and streams, and are most abundant
at the higher temperatures of midsummer. Cyclotella
is a similar form that does not, as a rule, form filaments.



Diatoms



Its cells are very small, and easily overlooked, "since
they largely escape the finest nets and are only to be




FIG. 36. A nearly pure culture of Meridion, showing colonies of
various sizes.

gathered from the water by filtering. Often, however,
their abundance compensates for their size. Kofoid
found their average number in the waters of the Illinois



H4 Aquatic Organisms

River to be 36,558,462 per cubic meter of water, and he
considered them as one of the principal sources of food
supply of Entomostraca and other microscopic aquatic
animals. Stephanodiscus (/) is distinguished by the
long, hyaline filaments that radiate from the ends of the
box, and that serve to keep it in the water. A species
of Stephanodiscus having shorter and more numerous
filaments is common in the open waters of Cayuga Lake
in spring.

The cells of Meridian are wedge-shaped, and grouped
together side by side, they form a flat spiral ribbon of
very variable length, sometimes in one or more com-
plete turns, but oftener broken into small segments.
This form abounds in the brook beds about Ithaca,
covering them every winter with an amber -tinted or
brownish ooze, often of considerable thickness. It
appears to thrive best when the temperature of the
water is near o C. Its richest growth is apparent after
the ice leaves the brooks in the spring. As a source of
winter food for the lesser brook-dwelling animals, it is
doubtless of great importance. A view of a magni-
fied bit of the ooze is shown in figure 36.

The colonies of Asterionella (n) whose cells, adhering
at a single point, radiate like the spokes of a wheel, are
common in the open waters of all our lakes and large
streams. It is a common associate of Cyclotella, and of
Tabellaria and other band-forming species, and is often
more abundant than any of these. The open waters of
Lake Michigan and of Cayuga Lake are often yellowish
tinted because of its abundance in them. Late spring
and fall (especially the former) after the thermal over-
turn and complete circulation of the water are the
seasons of its maximum development. Asterionella
abounds in water reservoirs, where, at its maxima, it
sometimes causes trouble by imparting to the water an
aromatic or even a decidedly "fishy" odor and an
unpleasant taste.



Diatoms



Campylodiscus (o and p) is a saddle-shaped diatom of
rather local distribution. It is found abundantly in the
ooze overspreading the black muck bottom of shallow
streams at the outlet of bogs. In such places in the
upper reaches of the tributaries of Fall Creek near
Ithaca it is so abundant as to constitute a large part of
the food of a number of denizens of the bottom mud
notably of midge larvae, and of nymphs of the big
Mayfly, Hexagenia.

These are a few a very few of the more important
or more easily recognized diatoms. Many others will
be encountered anywhere, the littoral forms especially
being legion. Stalked forms like Cocconema (fig. 355 and
fig- 37) will be found attached to every solid support.
And minute close-clinging epiphytic diatoms, like

Cocconeis and Epithemia will be

found thickly besprinkling the
green branches of many sub-
merged aquatics. These adhere
closely by the flat surface of one
valve to the epidermis of aquatic
mosses.

In open lakes, also, there are
other forms of great importance,
such asDiatoma, Fragillaria, etc.,
growing in flat ribbons, as does
Tabellaria. It is much to be
regretted that there are, as yet,
no readily available popular
guides to the study of a group,
so important and so interesting.
Equipped with a plancton net and a good microscope,
the student would never lack for material or for prob-
lems of fascinating interest.




FIG. 37. A stalked colony
Cocconema.



II 6 Aquatic Organisms



Desmids This is a group of singularly beautiful
unicellular fresh-water algae. Desmids are, as a rule,
of a refreshing green color, and their symmetry of form
and delicacy of sculpturing are so beautiful that they
have always been in favor with microscopists. So




FIG. 38. A good slide-mount from a Closterium culture
as it appears under a pocket lens. Two species.

numerous are they that their treatment has of late been
relegated to special works. Here we can give only a
few words concerning them, with illustrations of some
of the commoner forms.

Desmids may be recognized by the presence of a clear
band across the middle of each cell, (often emphasized
by a corresponding median constriction) dividing it
symmetrically into two semicells. Superficially they
appear bicellular (especially in such forms as Cylindro-



Desmids



117



cystis, fig. 40 e) , but there is a single nucleus, and it lies
in the midst of the transparent crossband. The larger
ones, such as Closterium (fig. 38) may be recognized with
the unaided eye, and may be seen clearly with a pocket
lens. Because it will grow per-
ennially in a culture jar in a
half -lighted window, Closterium
is a very well known labora-
tory type.

Division is transverse and sep-
arates between the semicells.
Its progress in Closterium is
shown in figure 39, in a series of
successive stages that were photo-
graphed between 10 P. M. and 3
A. M. Division normally occurs
only at night.

In a few genera (Gonatozygon,
(fig. 4oa) Desmidium, etc.) the
cells after division remain at-
tached, forming filaments.

Desmids are mainly free float-
ing and grow best in still waters.
They abound in northern lakes
and peat bogs. They prefer the
waters that run off archaean
rocks and few of them flourish
in waters rich in lime. A few
occur on mosses in the edges of
waterfalls, being attached to the
mosses by a somewhat tenacious gelatinous invest-
ment. One can usually obtain a fine variety of
desmids by squeezing wisps of such water plants
as Utricularia and Sphagnum, over the edge of a
dish, and examining the run-off. The largest genus of
the group and also one of the most widespread is




FIG.



39. Photomicrographs
of a Closterium dividing.
The lowermost figure is
one of the newly formed
daughter cells, not yet
fully shaped.



Aquatic Organisms



b g r^




FIG. 40. Desmids.



Filamentous Conjugates



119



Cosmarium (fig. 40 s). The
most bizarre forms are found
in the genera Micrasterias (figs.
40 q and r) and Staurastrum.
These connect in form
through Euastrum (fig. 40 o)
Tetmemorus (fig. 40 n) Netrium
(fig. 40 d), etc., with the sim-
pler forms which have little
differentiation of the poles of
the cell; and these, especially
Spirotaenia (fig. 40 b) and Gon-
atozygon (fig. 40 a) connect
with the filamentous forms
next to be discussed.

The Filamentous Conjugates
This is the group of fila-
mentous algae most closely
allied with the desmids. It
includes three common genera
(fig. 41) Spirpgyra, Zygnema,
and Mougeotia. The first of these being one of
the most widely used of biological " types" is known
to almost every laboratory student. Its long, green,
unbranched, slippery filaments are easily recognized
among all the other greenery of the water by their
beautiful spirally -wound bands of chlorophyl. The
other common genera have also distinctive chlorophyl
arrangement. Zygnema has a pair of more or less
star-shaped green masses in each cell, one on either side
of the central nucleus. In Mougeotia the chlorophyl




FIG. 41. Filamentous con-
jugates.

a. Spirogyra; b, flat view, and c,
edgewise view of the chlorophyl
plate in cells of Mougeotia,' d,
Zygnema.



a, a little more than two cells g Docidium baculum

from a filament of Gonatozygon h Docidium undulatum

b Spirotcenia i Closterium pronum

c Mesolcenium j Closterium rostratum

d Netrium k Closterium moniliferum

e Cylindrocystis I Closterium ehrenbergi

f Penium m Pleurotcenium



n Tetmemorus

o Euastrum didelta

p Euastrum verrucosum

q Micrasterias oscitans

r Micrasterias americana; (for

a third species see page 53).
s Cosmarium, face view, and

outline as seen from the side



I2O Aquatic Organisms

is in a median longitudinal plate, which can rotate in
the cell : it turns its thin edge upward to the sun, but
lies broadside exposed to weak light. Spirogyra is
the most abundant, especially in early spring where it
is found in the pools ere the ice has gone out. All, being
unattached (save as they become entangled with rooted
aquatics near shore), prefer quiet waters. Immense
accumulations of their tangled filaments often occur on
the shores of shallow lakes and ponds, and with the
advance of spring and subsidence of the water level,
these are left stranded upon the shores. They chiefly
compose the ' 'blanket-moss" of the fishermen. They
settle upon and smother the shore vegetation, and in
their decay they sometimes give off bad odors. Some-
times they are heaped in windrows on shelving beaches,
and left to decay.

We most commonly see them floating at the surface
in clear, quiet, spring-fed waters in broad filmy masses
of yellowish green color, which in the sunlight fairly
teem with bubbles of liberated oxygen. These dense
masses of filaments furnish a home and shelter for a
number of small animals, notably Haliplid beetle larvae
and punkie larvae among insects; and entanglement
by them is a peril to the lives of others, notably certain
Mayfly larvae (Blasturus). The rather large filaments
afford a solid support for hosts of lesser sessile algae;
and their considerable accumulation of organic contents
is preyed upon by many parasites. Their role is an
important one in the economy of shoal waters, and its
importance is due not alone to their power of rapid
growth, but also to their staying qualities. They hold
their own in all sorts of temporary waters by develop-
ing protected reproductive cells known as zygospores,
which are able to endure temporary drouth, or other
untoward conditions. Zygospores are formed by the
fusion of the contents of two similar cells (the process



Siphon Algae



121



is known as conjugation, whence the group name) and
the development of a protective wall about the result-
ing reproductive body. This rests for a time like a seed,
and on germinating, produces a new filament by the
ordinary process of cell division. These filamentous
forms share this reproductive process with the desmids,
and despite the differences in external aspect it is a
strong bond of affinity between the two groups.

The siphon algce This
peculiar group of green
algae contains a few forms
of little economic con-
sequence but of great
botanical interest. The
plant body grows out in
long irregularly branch-
ing filaments which,
though containing many
nuclei, lack cross par-
titions. The filaments
thus resemble long open
tubes, whence the name
siphon algae. There are two common genera Vau-
cheria and Botrydium (fig. 42). Both are mud-lov-
ing, and are found partly out of the water about as
often as wholly immersed. Vaucheria develops long,
crooked, extensively interlaced filaments which occur in
dense mats that have suggested the name ' 'green felt."
These felted masses are found floating in ponds, or
lying on wet soil wherever there is light and a con-
stantly moist atmosphere (as, for example, in green-
houses, where commonly found on the soil in pots).
Botrydium is very different and much smaller. It has
an oval body with root -like branches growing out from
the lower end to penetrate the mud. It grows on the
bottom in shoal waters, and remains exposed on the




FIG. 42. Two siphon algae.

A , Botrydium; B, a small fruiting portion of a
filament of Vaucheria.; ov, ovary; sp, spermary.



122 Aquatic Organisms

mud after the water has receded, dotting the surface
thickly, as with greenish beads of dew.

The water net and its allies The water net (Hydro-
dictyori) wherever found, is sure to attract attention by
its curious form. It is a cylindric sheet of lace-like
tissue, composed of slender green cells that meet at




FIG. 43. A rather irregular portion of a sheet of water net
(Hydrodictyon )

their ends, usually by threes, forming hexagonal meshes
like bobbinet (fig. 43). Such colonies may be as broad
as one's hand, or microscopic, or of any intermediate
size; for curiously enough, cell division and cell
growth are segregated in time. New colonies are
formed by repeated division of the contents of single



The Water Nets 123



cells of the old colonies. A new complete miniature
net is formed within a single cell; and after its escape
from the old cell wall, it grows, not by further division,
but by increase in size of its constituent cells.

Water net is rather local and sporadic in occurrence,
but it sometimes develops in quantities sufficient to fill
the waters of pools and small ponds.




FIG. 44.



^^IH^HI^Bl^BH^HBHH^HMi

Pediastrum: Several species from the plancton of
Cayuga Lake.



Pediastrum is a closely related genus containing a
number of beautiful species, some of which are common
and widespread. The cells of a Pediastrum colony are
arranged in a roundish flat disc, and those of the outer-
most row are usually prolonged into radiating points.
Several species are shown in figure 44. In the open-



I2 4



Aquatic Organisms



meshed species the inner cells can be seen to meet by
threes about the openings, quite as in the water net;
but the cells are less elongate and the openings smaller.
Five of the seven specimens shown in the figure lack
these openings altogether.

New colonies are formed within single cells, as in
Hydrodictyon. In our figure certain specimens show
marginal cells containing developing colonies. One
shows an empty cell wall from whence a new colony has
escaped.

Other green algcz
We have now men-
tioned a few of the
more strongly
marked groups of the
green algae. There
are other forms, so
numerous we may
not even name them
here, many of which
are common and
widely dispersed.
We shall have space
to mention only a
few of the more im-



& f\




FIG. 45. Filamentous Green Algae.



a, Ulothrix; b, (Edogonium, showing characteristic
annulate appearance at upper end of cell; c,
Conferva (Tribonema); d, Dra
West).



Iraparnaldia. (After



portant among them,

and we trust that

the accompanying figures will aid in their recognition.

Numerous and varied as they are, we will dismiss them

from further consideration under a few arbitrary form

types.

i. Simple filamentous forms. Of such sort are
Ulothrix, (Edogonium, Conferva, etc., (fig. 45). Ulo-
thrix is common in sunny rivulets and pools, especially
in early spring, where its slender filaments form masses



Other Green Algae



125



half floating in the water. The cells are short, often no
longer than wide, and each contains a single sheet of




FIG. 46. A spray of Cladophora, as it appears when
outspread in the water, slightly magnified.

chlorophyl, lining nearly all of its lateral wall. CEdogo-
nium is a form with stouter filaments composed of
much longer cells, within which the chlorophyl is dis-



126



Aquatic Organisms



posed in anastomosing bands. The thick cell walls,
some of which show a peculiar cross striation near one
end of the cell, are ready means of recognition of the
members of this great genus. The filaments are
attached when young, but break away and float freely
in masses in quiet waters when older; it is thus they
are usually seen. Conferva (Tribonema) abounds in
shallow pools, especially in spring time. Its filaments
are composed of elongate cells containing a number of

separate disc-like chlor-
ophyl bodies. The cell
wall is thicker toward
the ends of the cell, and
the filaments tend to
break across the middle,
forming pieces (halves of
two adjacent cells) which
appear distinctly H-
shaped in optic section.
This is a useful mark
for their recognition. It
will be observed that
these then are similar
in form and habits to
the filamentous conju-
gates discussed above,
but they have not the
peculiar form of chlor-

ophyl bodies characteristic of that group. (Eodgonium
is remarkable for its mode of reproduction.

2. Branching filamentous forms Of such sort are a
number of tufted sessile algae of great importance:
Cladophora, which luxuriates in the dashing waterfall,
which clothes every wave-swept boulder and pier with
delicate fringes of green, which lays prostrate its pliant
sprays (fig. 46) before each on-rushing wave, and lifts




FIG. 47. Two species of Chaetophora,
represented by several small hemi-
spherical colonies of C. pisiformis and
one large branching colony of
C. incrassata.



Other Green Algae 127

them again uninjured, after the force of the flood is
spent. And Ch&tophora (fig. 47; also fig. 89 on p. 182) ;
which is always deeply buried under a transparent mass




FIG. 48. Chaetophora (either species) crushed and outspread
in its own gelatinous covering and magnified to show the
form of the filaments.



of gelatin; which forms little hemispherical hillocks of



Online LibraryJames G. (James George) NeedhamThe life of inland waters; an elementary text book of fresh-water biology for students → online text (page 7 of 26)