Algæ and their Growth--Desmidiaceæ, where found--Diatoms, their
Flinty Deposit--Volvox--Mould, Blight, and Mildew--Mosses and
Ferns--Mare’s-Tail and the Spores--Common Sea-weeds and their Growth.
On Plate IV. will be seen many examples of the curious vegetables
called respectively algæ and fungi, which exhibit some of the lowest
forms of vegetable life, and are remarkable for their almost universal
presence in all parts of this globe, and also almost all conditions of
cold, heat, or climate. Many of them are well known under the popular
name of sea-weeds, others are equally familiar under the titles of
“mould,” “blight,” or “mildew,” while many of the minuter kinds exhibit
such capability of motion, and such apparent symptoms of volition, that
they have long been described as microscopic animalcules, and thought
to belong to the animal rather than to the vegetable kingdoms.
Fig. 1 represents one of the very lowest forms of vegetable life, being
known to the man of science as the Palmella, and to the general public
as “gory dew.” It may be seen on almost any damp wall, extending in red
patches of various sizes, looking just as if some blood had been dashed
on the wall, and allowed to dry there. With a tolerably powerful
lens this substance can be resolved into the exceedingly minute cells
depicted in the figure. Generally, these cells are single, but in many
instances they are double, owing to the process of subdivision by which
the plant grows, if such a term may be used.
Fig. 2 affords an example of another very low form of vegetable, the
Palmoglæa, that green slimy substance which is so common on damp
stones. When placed under the microscope, this plant is resolvable
into a multitude of green cells, each being surrounded with a kind of
gelatinous substance. The mode of growth of this plant is very simple.
A line appears across one of the cells, and after a while it assumes a
kind of hour-glass aspect, as if a string had been tied tightly round
its middle. By degrees the cell fairly divides into two parts, and then
each part becomes surrounded with its own layer of gelatine, so as to
form two separate cells, placed end to end.
One of the figures, that on the right hand, represents the various
processes of “conjugation,” _i.e._ the union and fusion together of two
cells. Each cell throws out a little projection; these meet together,
and then uniting, form a sort of isthmus connecting the two main
bodies. This rapidly widens, until the two cells become fused into one
large body. The whole subject of conjugation is very interesting, and
is treated at great length in the _Micrographic Dictionary_ of Messrs.
Griffith and Henfrey, a work to which the reader is referred for
further information on many of the subjects that, in this small work,
can receive but a very hasty treatment.
Few persons would suppose that the slug-like object on Fig. 3, the
little rounded globules with a pair of hair-like appendages, and the
round disc with a dark centre, are only different forms of the same
organism. Such, however, is the case, and these are three of the
modifications which the Protococcus undergoes. This vegetable may be
seen floating like green froth on the surface of rain-water.
On collecting some of this froth and putting it under the microscope,
it is seen to consist of a vast number of little green bodies, moving
briskly about in all directions, and guiding their course with such
apparent exercise of volition that they might very readily be taken for
animals. It may be noticed that the colour of the plant is sometimes
red, and in that state it has been called the Hæmatococcus.
The “still” state of this plant is shown in the round disc. After a
while the interior substance splits into two portions; these again
subdivide, and the process is repeated until sixteen or thirty-two
cells become developed out of the single parent-cell. These little ones
then escape, and, being furnished with two long “cilia” or thread-like
appendages, whirl themselves merrily through the water. When they have
spent some time in this state, growing all the while, they lose their
cilia, become clothed with a strong envelope, and pass into the still
stage from which they had previously emerged. This curious process is
repeated in endless succession, and causes a very rapid growth of the
plant. The moving bodies are technically called zoospores, or living
spores, and are found in many other plants besides those of the lowest
order.
IV.
FIG.
1. Gory Dew, Palmella cruenta
2. Palmoglæa macrococca
3. Protococcus pluvialis,
_a_, in its motile,
_b_, in its fixed state,
_c_, zoospores
4. Closterium
5. Ditto, end more magnified
6. Pediastrum
7. Scenedesmus
8. Oscillatoria
9. Spirogyra
10. Tyndaridea
11. Do. spore
12. Sphærozosma
13. Chlorococcus
14. Scenedesmus
15. Pediastrum, to show cells
16. Ankistrodesmus
17. Cosmarium
18. Desmidium
19. Cosmarium, formation of Resting Spore
20. Cocconema lanceolatum
21. Diatoma vulgare
Do. larger frustules, at the side
22. Volvox globator
Do. single green body, above
23. Synedra
24. Gomphonema acuminatum
Do. larger frustules, below
25. Yeast
26. Sarcina ventriculi
27. Eunotia diadema
28. Melosira varians
Do. two bleached frustules
29. Cocconeis pediculus
30. Achnanthes exilis
31. Navicula amphisbœna
32. Uredo, “Red-rust” of corn
33. Puccinea, Mildew of corn
34. Botrytis, mould on grapes
Do. Sporules, beside it
35. Do. parasitica, Potato blight
36. Ectocarpus siliculosus
37. Ulva latissima
38. Polypodium
Do. single spore, below
39. Moss capsule, Hypnum
40. Mare’s tail, Equisetum, _a_
Do. do. _b_ and _c_
41. Porphyra laciniata
[Illustration: IV.]
On Fig. 13 is delineated a very minute plant, called from its colour
Chlorococcus. It may be found upon tree-trunks, walls, etc., in the
form of green dust, and has recently been found to take part in forming
the first stage of lichens.
A large and interesting family of the “confervoid algæ,” as these low
forms of vegetable life are termed, is the Desmidiaceæ, called in more
common parlance desmids. A few examples of this family are given in
Plate IV.
They may be found in water, always preferring the cleanest and the
brightest pools, mostly congregating in masses of green film at the
bottom of the water, or investing the stems of plants. Their removal
is not very easy, but is best accomplished by very carefully taking up
this green slippery substance in a spoon, and straining the water away
through fine muslin. They may also be separated by allowing a ring,
covered with muslin, to float upon the surface of the water collected
in a jar, for, being great lovers of light, they assemble where it
is most abundant. An opaque jar should be used. For preservation,
glycerine-gelatine seems to be the best fluid. A very full and accurate
description of these plants may be found in Ralfs’ _British Desmidieæ_.
Fig. 4 represents one of the species of Closterium, more than twenty
of which are known. These beautiful objects can be obtained from the
bottom of almost every clear pool, and are of some interest on account
of the circulating currents that may be seen within the living plants.
A high power is required to see this phenomenon clearly. The Closteria
are reproduced in various ways. Mostly they divide across the centre,
being joined for a while by two half-cells. Sometimes they reproduce
by means of conjugation, the process being almost entirely conducted
on the convex sides. Fig. 5 represents the end of a Closterium, much
magnified in order to show the actively moving bodies contained within
it.
Fig. 16 is a supposed desmid, called Ankistrodesmus, and presumed to be
an earlier stage of Closterium.
Fig. 6 is a very pretty desmid called the Pediastrum, and valuable to
the microscopist as exhibiting a curious mode of reproduction. The
figure shows a perfect plant composed of a number of cells arranged
systematically in a star-like shape; Fig. 15 is the same species
without the colouring matter, in order to show the shape of the cells.
The Pediastrum reproduces by continual subdivision of the contents of
each cell into a number of smaller cells, termed “gonidia” on account
of their function on the perpetuation of the species. When a sufficient
number has been formed, they burst through the envelope of the original
cell, taking with them a portion of its internal layer, so as to form
a vesicle, in which they move actively. In a few minutes they arrange
themselves in a circle, and after a while they gradually assume the
perfect form, the whole process occupying about two days. Fig. 18
exhibits an example of the genus Desmidium. In this genus the cells are
either square or triangular in their form, having two teeth at their
angles, and twisted regularly throughout their length, causing the wavy
or oblique lines which distinguish them. The plants of this genus are
common, and may be found almost in any water. I may as well mention
that I have obtained nearly all the preceding species, together with
many others, from a little pond on Blackheath.
Fig. 7 is another desmid called Scenedesmus, in which the cells are
arranged in rows of from two to ten in number, the cell at each
extremity being often furnished with a pair of bristle-like appendages.
Fig. 14 is another species of the same plant, and both may be found in
the water supplied for drinking in London, as well as in any pond.
A common species of desmid is seen at Fig. 12, called Sphærozosma,
looking much like a row of stomata set chainwise together. It
multiplies by self-division.
Fig. 17 is a specimen of desmid named Cosmarium, plentifully found
in ponds on heaths and commons, and having a very pretty appearance
in the microscope, with its glittering green centre and beautifully
transparent envelope. The manner in which the Cosmarium conjugates is
very remarkable, and is shown at Fig. 19.
The two conjugating cells become very deeply cleft, and by degrees
separate, suffering the contents to pour out freely, and, as at present
appears, without any envelope to protect them. The mass, however,
soon acquires an envelope of its own, and by degrees assumes a dark
reddish-brown tint. It is now termed a sporangium, and is covered with
a vast number of projections, which in this genus are forked at their
tip, but in others, which also form sporangia, are simply pointed. The
Closteria conjugate after a somewhat similar manner, and it is not
unfrequent to find a pair in this condition, but in their case the
sporangium is quite smooth on its surface.
Another very remarkable family of confervoid algæ is that which is
known under the name of Oscillatoriæ, from the oscillating movement
of the plant. They are always long and filamentous in character, and
may be seen moving up and down with a curious irregularity of motion.
Their growth is extremely rapid, and may be watched under a tolerably
powerful lens, thus giving many valuable hints as to the mode by
which these plants are reproduced. One of the commonest species is
represented at Fig. 8.
Figs. 9, 10, and 11 are examples of another family, called technically
the Zygnemaceæ, because they are so constantly yoked together by
conjugation. They all consist of a series of cylindrical cells, set end
to end, and having their green contents arranged in similar patterns.
Two of the most common and typical species are here given.
Fig. 9 is the Spirogyra, so called from the spiral arrangement of
the chlorophyll; and Fig. 10 is the Tyndaridea, or Zygnema, as it is
called by some writers. A casual inspection will show how easy it is
to distinguish the one from the other. Fig. 11 represents a portion of
the Tyndaridea during the process of conjugation, showing the tube of
connection between the cells and one of the spores.
* * * * *
We now arrive at the diatoms, so called because of their method of
reproduction, in which it appears as if a cut were made right along the
original cell. The commonest of these plants is the Diatóma vulgáre,
seen in Fig. 21 as it appears while growing. The reproduction of this
plant is effected by splitting down the centre, each half increasing
to the full size of the original cell; and in almost every specimen of
water taken from a pond, examples of this diatom undergoing the process
of division will be distinguished. It also grows by conjugation. The
diatoms are remarkable for the delicate shell or flinty matter which
forms the cell skeleton, and which will retain its shape even after
intense heat and the action of nitric acid. While the diatoms are
alive, swimming through the water, their beautiful markings are clearly
distinct, glittering as if the form were spun from crystalline glass.
Just above the figure, and to the right hand, are two outlines of
single cells of this diatom, the one showing the front view and the
other the profile.
Fig. 20 is an example of a diatom--Cocconéma lanceolátum--furnished
with a stalk. The left-hand branch sustains a “frustule” exhibiting the
front view, while the other is seen sideways.
Another common diatom is shown in Fig. 23, and is known by the name of
Synedra. This constitutes a very large genus, containing about seventy
known species. In this genus the frustules are at first arranged upon
a sort of cushion, but in course of time they mostly break away from
their attachment. In some species they radiate in every direction from
the cushion, like the spikes of the ancient cavalier’s mace.
Fig. 24 is another stalked diatom called Gomphonéma acuminátum, found
commonly in ponds and ditches. There are nearly forty species belonging
to this genus. A pair of frustules are also shown which exhibit the
beautiful flinty outline without the coloured contents (technically
called endochrome).
Fig. 27 is a side view of a beautiful diatom, called Eunótia diadéma
from its diadem-like form. There are many species of this genus. When
seen upon the upper surface, it looks at first sight like a mere row of
cells with a band running along them; but by careful arrangement of the
light its true form may easily be made out.
Fig. 28 represents a very common fresh-water diatom, named Melosíra
várians. The plants of this genus look like a cylindrical rod composed
of a variable number of segments, mostly cylindrical, but sometimes
disc-shaped or rounded. An end view of one of the frustules is seen
at the left hand, still coloured with its dots of “endochrome,” and
showing the cylindrical shape. Immediately above is a figure of another
frustule seen under both aspects with the endochrome removed.
A rather curious species of diatom, called Cocconeïs pedículus, is
seen at Fig. 29 as it appears on the surface of common water-cress.
Sometimes the frustules, which in all cases are single, are crowded
very closely upon each other and almost wholly hide the substance on
which they repose. Fig. 30 is another diatom of a flag-like shape,
named Achnanthes, having a long slender filament attached to one end
of the lower frustule, representing the flag-staff. There are many
wonderful species of such diatoms, some running almost end to end like
a bundle of sticks, and therefore called Bacillária; others spreading
out like a number of fans, such as the genus Licmophora; while some
assume a beautiful wheel-like aspect, of which the genus Meridion
affords an excellent example.
A very remarkable, and not uncommon, fresh-water diatom is the
Bacillária paradóxa. It looks, when at rest, like a broad brown ribbon
of varying length. The diatoms lie across the ribbon, on edge, and
slide upon each other exactly like the ladders of a fire-escape, so
that the broad ribbon is converted into a fine long thread, which
speedily closes up again into the original ribbon, and so _da capo_.
The reason for this movement, and how it is effected, is absolutely
unknown; indeed, nothing certain is known as to the way in which
diatoms move, nor has ever a probable guess yet been made.
The last of the diatoms which we shall be able to mention in this
work is that represented on Fig. 31. The members of this genus have
the name of Navícula, on account of their boat-like shape and their
habit of gliding through the water in a canoe-like fashion. There are
many species of this genus, all of which are notable for the graceful
and varied courses formed by their outlines, and the extreme delicacy
of their markings. In many species the markings are so extremely
minute that they can only be made out with the highest powers of the
microscope and the most careful illumination, so that they serve as
test objects whereby the performance of a microscope can be judged by a
practical man.
* * * * *
The large spherical figure in the centre of Plate IV. represents an
example of a family belonging to the confervoid algæ, and known by the
name of Volvox globator. There seems to be but one species known.
This singular plant has been greatly bandied about between the
vegetable and animal kingdoms, but seems now to be satisfactorily
settled among the vegetables. In the summer it may be found in pools
of water, sufficiently large to be visible to the naked eye, like a
little green speck proceeding slowly through the water. When a moderate
power is used, it appears as shown in the figure, and always contains
within its body a number of smaller individuals, which after a while
burst through the envelope of the parent and start upon an independent
existence. On a closer examination, a further generation may be
discovered even within the bodies of the children. The whole surface is
profusely covered with little green bodies, each being furnished with
a pair of movable cilia, by means of which the whole organism is moved
through the water. These bodies are analogous to the zoospores already
mentioned, and are connected with each other by a network of filaments.
Reproduction also takes place by conjugation as in other algæ. A
more magnified representation of one of the green bodies is shown
immediately above the larger figure. The volvox is apt to die soon when
confined in a bottle.
Fig. 25 is the common yeast-plant, consisting simply of a chain of
cells, which increase by budding, and only form spores when they have
exhausted the nutriment in the fluid in which they live. Fig. 26 is
a curious object, whose scientific name is Sárcina ventrículi. It is
found in the human stomach. Similar forms are often to be found in the
air; for instance, a piece of cocoa-nut will exhibit this, and many
other kinds of Bacteria and moulds, after a few days’ exposure to the
air, preferably in a dark cupboard.
We now come upon a few of the blights and mildews. A very interesting
series of forms is first to be alluded to. Upon the bramble-leaf may
often be found spots, at first red, then orange, then reddish black.
These are known as Œcidium berberidis. Fig. 32 shows the “red-rust”
of wheat, the Urédo; and Fig. 33 is the mildew of corn, known as
Puccinia. The interest lies in the fact that these three forms are
successive stages in the life-history of the same plant. Another
species of Urédo, together with a Phragmídium, once thought to be
another kind of fungus, is seen on a rose-leaf on Plate V. Fig. 1.
On Fig. 10, however, of the same Plate, the Phragmídium may be seen
proceeding from Urédo, thus proving them to be but two states of the
same plant. There is room for any amount of observation and work in
connection with the life-histories of many of these fungi.
Another species of Puccinia, found on the thistle, is shown on Plate
V. Fig. 7. Fig. 34 is the mould found upon decaying grapes, and called
therefrom, or from the clustered spores, Botrýtis. Some of the detached
spores are seen by its side. Fig. 35 is another species of the same
genus, termed Botrýtis parasítica, and is the cause of the well-known
“potato-disease.”
The mosses and ferns afford an endless variety of interesting objects
to the microscopist; but as their numbers are so vast, and the details
of their structure so elaborate, they can only be casually noticed in
the present work. Fig. 38 represents a spore-case of the Polypodium,
one of the ferns, as it appears while in the act of bursting and
scattering the contents around. One of the spores is seen more
magnified below. The spore-cases of many ferns may be seen bursting
under the microscope, and have a very curious appearance, writhing and
twisting like worms, and then suddenly filling the field with a cloud
of spores. Fig. 9, Plate V., is a piece of the brown, chaff-like, scaly
structure found at the base of the stalk of male fern cells, showing
the manner in which a flat membrane is formed. Fig. 39 is a capsule of
the Hypnum, one of the mosses, showing the beautiful double fringe with
which its edge is crowned. Fig. 2, Plate V., is the capsule of another
moss, Polytríchum, to show the toothed rim; on the right hand is one of
the teeth much more magnified.
Fig. 3, Plate V., is the capsule of the Jungermannia, one of the
liverworts, showing the “elaters” bursting out on every side, and
scattering the spores. Fig. 4 is a single elater much magnified,
showing it to be a spirally coiled filament, that, by sudden expansion,
shoots out the spores just as a child’s toy-gun discharges the arrow.
Fig. 5 is a part of the leaf of the Sphagnum moss, common in fresh
water, showing the curious spiral arrangement of secondary fibre which
is found in the cells, as well as the circular pores which are found
in each cell at a certain stage of growth. Just below, and to the
left hand, is a single cell greatly magnified, in order to show these
peculiarities more strongly. Fig. 8 is part of a leaf of Jungermannia,
showing the dotted cells.
Fig. 6, Plate V., is a part of a rootlet of moss, showing how it is
formed of cells elongated and joined end to end.
On the common mare’s-tail, or Equisétum, may be seen a very remarkable
arrangement for scattering the spores. On the last joint of the stem
is a process called a fruit-spike, being a pointed head around which
are set a number of little bodies just like garden-tables, with their
tops outward. One of these bodies is seen in Fig. 40. From the top of
the table depend a number of tiny pouches, which are called sporangia;
these lie closely against each other, and contain the spores. At the
proper moment these pouches burst from the inside, and fling out the
spores, which then look like round balls with irregular surfaces, as
shown in Fig. 40, _c_. This irregularity is caused by four elastic
filaments, knobbed at the end, which are originally coiled tightly
round the body of the spore, but by rapidly untwisting themselves cause
the spore to leap about, and so aid in the distribution. A spore with
uncoiled filaments is seen at Fig. 40, _b_. By breathing on them they
may be made to repeat this process at will.
Fig. 36 is a common little sea-weed, called Ectocarpus siliculósus,
that is found parasitically adhering to large plants, and is figured in
order to show the manner in which the extremities of the branches are
developed into sporangia. Fig. 37 is a piece of the common green laver,
Ulva latíssima, showing the green masses that are ultimately converted
into zoospores, and by their extraordinary fertility cause the plant to
grow with such rapid luxuriance wherever the conditions are favourable.
Every possessor of a marine aquarium knows how rapidly the glass sides
become covered with growing masses of this plant. The smaller figure
above is a section of the same plant, showing that it is composed of a
double plate of cellular tissue.
Fig. 41 is a piece of purple laver or “sloke,” Porphýra laciniáta, to
show the manner in which the cells are arranged in groups of four,
technically named “tetraspores.” This plant has only one layer of cells.
On Plate V. may be seen a number of curious details of the higher algæ.
Fig. 11 is the Sphacelária, so called from the curious capsule cells
found at the end of the branches, and termed sphacelæ. This portion
of the plant is shown more magnified in Fig. 12. Another sea-weed is
represented in Fig. 13, in order to show the manner in which the fruit
is arranged; and a portion of the same plant is given on a larger scale
at Fig. 14.
A very pretty little sea-weed called Cerámium is shown at Fig. 15; and
a portion showing the fruit much more magnified is drawn at Fig. 22.
Fig. 23 is a little alga called Myrionéma, growing parasitically on the
preceding plant.
Fig. 16 is a section of a capsule belonging to the Hálydris siliquósa,
showing the manner in which the fruit is arranged; and Fig. 17 shows
one of the spores more magnified.
Fig. 18 shows the Polysiphónia parasítica, a rather common species of
a very extensive genus of sea-weeds, containing nearly three hundred
species. Fig. 19 is a portion of the stem of the same plant, cut across
in order to show the curious mode in which it is built up of a number
of longitudinal cells, surrounding a central cell of large dimensions,
so that a section of this plant has the aspect of a rosette when placed
under the microscope. A capsule or “ceramídium” of the same plant is
shown at Fig. 20, for the purpose of exhibiting the pear-shaped spores,
and the mode of their escape from the parent-cell previous to their
own development into fresh plants. The same plant has another form
of reproduction, shown in Fig. 21, where the “tetraspores” are seen
imbedded in the substance of the branches. There is yet a third mode
of reproduction by means of “antheridia,” or elongated white tufts at
the extremities of the branches. The cells produced by these tufts
fertilise the rudimentary capsules, and so fulfil the function of the
pollen in flowering plants.
Fig. 25 is the Cladóphora, a green alga, figured to illustrate its mode
of growth; and Fig. 26 represents one of the red sea-weeds, Ptilóta
élegans, beautifully feathered, and with a small portion shown also
on a larger scale, in order to show its structure more fully. A good
contrast to this species is seen on Fig. 27, and the mode in which the
long, slender, filamentary fronds are built up of many-sided cells is
seen just to the left hand of the upper frond. Fig. 24 is a portion of
the lovely Delesséria sanguínea, given in order to show the formation
of the cells, as also the arrangement by which the indistinct nervures
are formed.
V.
FIG.
1. Rose Leaf, with fungus
2. Moss capsule, Polytrichum
3. Jungermannia, capsule
4. Do. an elater more magnified
5. Leaf of Moss, Sphagnum
6. Rootlet, Moss
7. Puccinia, from Thistle
8. Jungermannia, leaf
9. Scale from stalk of male fern
10. Uredo
11. Sphacelaria filicina
12. Do. top, more magnified
13. Seaweed, showing fruit
14. Do. fruit, more magnified
15. Ceramium
16. Capsule, Halidrys
17. Spore of do.
18. Polysiphonia parasitica
19. Do. stem, more magnified
20. Do. Capsule, tetraspores escaping
21. Do. fruit, another form
22. Ceramium, fruit
23. Myrionema, parasitic Seaweed
24. Delesseria sanguinea, Frond
25. Cladophora
26. Ptilota elegans
27. Enteromorpha clathrata
28. Nitophyllum laceratum
[Illustration: V.]
The figure on the bottom left-hand corner of Plate V. is a portion of
the pretty Nitophyllum lacerátum, a plant belonging to the same family
as the preceding one. The specimen here represented has a gathering
of spores upon the frond, in which state the frond is said to be “in
fruit.”
Fig. 27 represents a portion of the common sea-grass (_Enteromorpha_),
so common on rocks and stones between the range of high and low water.
On the left hand of the figure, and near the top, is a small piece of
the same plant much more magnified, in order to show the form of its
cells.