Algae, popularly known as sea-weeds, although many species are
inhabitants of fresh water, or grow on moist ground, may be briefly
described as cellular, flowerless plants, having no proper roots, but
imbibing nutriment by their whole surface from the medium in which
they grow. As far as has been ascertained, the total number of species
is about 9000 or 10,000. Many of them are microscopic, as the Desmids
and Diatoms, others, as Lessonia, and some of the larger Laminariae
(oarweeds), are arborescent, covering the bed of the sea around the
coast with a submarine forest; while in the Pacific, off the
northwestern shores of America, Nereocystis, a genus allied to
Laminaria, has a stem over 300 feet in length, which, although not
thicker than whipcord, is stout enough to moor a bladder,
barrel-shaped, six or seven feet long, and crowned with a tuft of
fifty leaves or more, each from thirty to forty feet in length. This
vegetable buoy is a favourite resting place of the sea otter; and
where the plant exists in any quantity, the surface of the sea is
rendered impassable to boats. The stem of Macrocystis, which "girds
the globe in the southern temperate zone," is stated to extend
sometimes to the enormous length of 1500 feet. It is no thicker than
the finger anywhere, and the upper branches are as slender as
pack-thread; but at the base of each leaf there is placed a buoy, in
the shape of a vesicle filled with air.
Although the worthlessness of Algae has been proverbial, as in the
"alga inutile" of Horace and Virgil's "projecta vilior alga," they are
not without importance in botanical economics. A dozen or more species
found in the British seas are made use of, raw or prepared in several
ways, as food for man. Of these edible Algae, Dr. Harvey considers the
two species of Porphyra, or laver, the most valuable. Berkeley says,
"The best way of preparing this vegetable or condiment, which is
extremely wholesome, is to heat it thoroughly with a little strong
gravy or broth, adding, before it is served on toast, a small quantity
of butter and lemon juice." A species of Nostoc is largely consumed in
China as an ingredient in soup. A similar use is made of Enteromorpha
intestinalis in Japan. Many species of fish and other animals, turtle
included, live upon sea-weed. Fucus vesiculosus is a grateful food for
cattle. In Norway, cattle, horses, sheep, and pigs are largely fed
upon it, and on our own coasts cattle eagerly browse on that and
kindred species at low water. In some northern countries, Fucus
serratus sprinkled with meal is used as winter fodder.
[Illustration: Fig. 1. Group of Sea-weeds (chiefly Laminariae)]
All the marine Algae contain iodine; and even before the value of that
substance in glandular complaints had been ascertained, stems of a
sea-weed were chewed as a remedy by the inhabitants of certain
districts of South America where goitre is prevalent. Chondrus crispus
and (Gigartina) mamillosa constitute the Irish moss of commerce, which
dissolves into a nutritious and delicate jelly, and the restorative
value of which in consumption doubtless depends in some degree on the
presence of iodine. The freshwater Algae not only furnish abundant and
nourishing food to the fish and other animals living in ponds and
streams, but by their action in the decomposition of carburetted
hydrogen and other noxious gases purify the element in which they
live, thus becoming important sanitary agents. The value of aquatic
plants in the aquarium is well known. A Chinese species of Gigartina
is much employed as a glue and varnish; and also much used in China in
the manufacture of lanterns and transparencies, and in that country
and Japan for glazing windows. Handles for table knives and forks,
tools, and other implements have been made from the thick stems of
oarweeds, and fishing lines from Chorda filum. Tripoli powder,
extensively used for polishing, consists mainly of the silicious
shells of Diatoms. On various parts of our coast, the coarser species
of sea-weed, now used as a valuable manure, were formerly extensively
burnt for kelp, an impure carbonate of soda. This industry, when
carried on upon a large scale, became a fruitful source of income to
some of the poorest districts in the kingdom, bringing, in the last
decade of last century, nearly L30,000 per annum into Orkney alone.
Since the production of soda from rock salt has become general, kelp
is now only burnt for the extraction of iodine, this being the easiest
way of obtaining that substance.
Although the vegetable structure and mode of reproduction are
essentially the same in all Algae, as regards the former they vary from
the simple cell, through cells arranged in threads, to a stem and
leaves simulating the vegetation of higher tribes. And although the
simpler kinds are obviously formed of threads, most of the more
compound may also be resolved into the same structure by maceration in
hot water or diluted muriatic acid. In substance some are mere masses
of slime or jelly, others are silky to the feel, horny, cartilaginous
or leather-like, and even apparently woody. A few species secrete
carbonate of lime from the water, laying it up in their tissues;
others cover themselves completely with that mineral, while some coat
themselves with silex or flint. Many Algae are beautifully coloured,
even when growing at depths to which very little light penetrates. As
in their vegetative organs, so in their reproductive, Algae exhibit
many modifications of structure without much real difference. In the
green sea-weeds reproduction is effected by simple cell division in
the unicellular species, and by spores resulting from the union of the
contents of two cells in the others. The red sea-weeds have a double
system of reproduction, a distinctly sexual one, by spores and
antheridia, and another by tetraspores, which by some are considered
to be of the nature of gemmae, or buds. The spores are generally
situated in distinct hollow conceptacles (favellae, ceramidium,
coccidium). The tetraspore is also sometimes contained in a
conceptacle. It consists of a more or less globular, transparent cell,
which when mature contains within it four (rarely three) sporules.
Reproduction in the olive sea-weeds is also double, by zoospores,
generally considered gemmae, and by spores and antherozoids, which is a
sexual process.
[Illustration: Fig. 2. A, Species of Gleocapsa, one of the
Palmelleae, in various stages. A becomes B, C, D, and E by
repeated division. Magnified 300 diameters.]
Following the classification adopted by Professor Harvey, which is
that generally employed in English systematic manuals, we divide the
order into three sub-orders, named from the prevailing colour of their
spores. 1. Chlorospermeae, with green spores; 2. Rhodospermeae, with red
spores; and 3. Melanospermeae, with olive-coloured spores. The entire
plant in the first group is usually grass-green, but occasionally
olive, purple, blue, and sometimes almost black; in the second it is
some shade or other of red, very seldom green; and in the third, while
generally olive green, it is occasionally brown olive or yellow.
The Chlorospermeae are extremely varied in form, often threadlike, and
are propagated either by the simple division of the contents of their
cells (endochrome), by the transformation of particular joints, or by
the change of the contents of the cells into zoospores, which are
cells moving freely in water by means of hairlike appendages. In their
lower forms they are among the most rudimentary of all plants, and
thus of special interest physiologically, as representing the
component parts of which higher plants are formed. They are subdivided
into twelve groups, as follows:
The first group, Palmelleae, are unicellular plants, the cells of which
are either free or surrounded by a gelatinous mass, and they are
propagated by the division of the endochrome. One of the most
remarkable of the species of this family is Protococcus cruentus,
which is found at the foot of walls having a northern aspect, looking
as if blood had been poured out on the ground or on stones.
Protococcus nivalis, again, is the cause of the red snow, of which
early arctic navigators used to give such marvellous accounts.
(Fig. 2.)
[Illustration: Fig. 3. A, Fragment of a Filament of Zygnema,
one of the Conjugateae; B, Closterium; C, Euastrium; two
desmids.]
The Desmideaceae, together with the plants of the next succeeding
group, are favourite subjects of investigation or observation by the
possessors of microscopes, an attention they merit from the beauty and
variety of their forms. They are minute plants of a green colour,
consisting of cells generally independent of each other, but sometimes
forming brittle threads or minute fronds, and are reproduced by spores
generated by the conjugation of two distinct individuals. The process
of conjugation in Desmids and Diatoms consists in the union of the
endochrome of two individuals, each of which in these families is
composed of a single cell. This ultimately forms a rounded body or
resting spore, which afterwards germinates, the resulting plant not
however acquiring the normal form until the third generation. (Fig.
3.)
The Diatomaceae, closely allied to the preceding group in structure and
reproduction, are however distinguished from them by their flinty
shells, which are often beautifully sculptured. Their endochrome is a
golden brown, instead of green as in the Desmideaceae. The latter,
also, are confined to fresh water, while the Diatomaceae are found,
though not exclusively, in the sea, where their shells sometimes,
microscopically minute as they are individually, form banks extending
several hundred miles. It is stated that in the collection made by Sir
Joseph Hooker in the Himalayas the species closely resemble our own.
In the next group, Confervaceae, we are introduced to forms more like
the general notion of what a plant should be. The individuals of which
it consists are composed of threads, jointed, either simple or
branched, mostly of a grass-green colour, and propagating either by
minute zoospores or by metamorphosed joints. They are found both in
fresh and salt water, and in damp situations. The number of species is
very great. A considerable number consist of unbranched threads; the
branched forms grow sometimes so densely as to assume the form of
solid balls. After floods, when the water stands for several days,
they sometimes increase to such an extent, as to form on its
subsidence a uniform paper-like stratum, which while decomposing is
extremely disagreeable. The name Conferva has been almost discontinued
as a generic title, the majority of British species being now ranged
under Clado- and Chaeto-phora. The latter are branched, and require
great care and attention in order to distinguish them, on account of
their general resemblance to each other. Good characters are however
to be found in their mode of branching and the form and comparative
size of the terminal joints.
The Batrachospermeae constitute a small but very beautiful group,
consisting of gelatinous threads variously woven into a branched
cylindrical frond. The branches are sometimes arranged, as in the
British species, so that the plants appear like necklaces. In colour
they pass from green, through intermediate shades of olive and purple,
to black. In common with some of the higher Algae, the threads of the
superficial branches send joints down the stem, changing it from
simple to compound. The native species are all fluviatile.
The Hydrodicteae are among the most remarkable of Algae. Hydrodictyon
utriculatum, the solitary British species, is found in the large pond
at Hampton Court, and in similar situations in various parts of the
country, but not very generally. It resembles a green purse or net,
from four to six inches in length, with delicate and regular meshes,
the reticulations being about four lines long. Its method of
reproduction is no less than its form. Each of the cells
forms within itself an enormous mass of small elliptic grains. These
become attached by the extremities so as to form a network inside the
cell, and, its walls being dissolved, a new plant is set free to grow
to the size of the parent Hydrodictyon.
The Nostochineae grow in fresh water, or attached to moist soil. They
consist of slender, beaded threads surrounded by a firm jelly, and
often spreading into large, wavy fronds. The larger beads on the
inclosed threads are reproductive spores. (Fig. 4, A.)
[Illustration: Fig. 4. A, Fragment of a Filament of Nostoc. B,
End of a Filament of Oscillatoria.]
The Oscillatoreae are another remarkable group, on account of the
peculiar animal-like motions they exhibit. They occur both in salt and
fresh water, and on almost every kind of site in which there is
sufficient moisture. The threads of which they are composed are
jointed, and generally unbranched; they are of various tints of blue,
red, and green, and, where their fructification has been ascertained,
are propagated by cell division. The most curious point about them is,
however, the movements of their fronds. According to Dr. Harvey, these
are of three kinds--a pendulum-like movement from side to side,
performed by one end, whilst the other remains fixed, so as to form a
pivot; a movement of flexure of the filament itself, the oscillating
extremity bending over from one side to the other, like the head of a
worm or caterpillar seeking something on its line of march; and
lastly, a simple onward movement of progression, the whole phenomenon
being, Dr. Harvey thinks, resolvable into a spiral onward movement of
the filament. Whatever is the cause of this motion, it is not, as used
to be supposed, of an animal nature; for the individuals of this group
are undoubted plants. (Fig. 4, B.) Several species of Rivularia,
belonging to the Oscillatoreae, are found both in the sea and in fresh
water. They are gelatinous, and have something of the appearance of
Nostoc, in aspect as well as in minute structure.
The Conjugatae are freshwater articulated Algae, which reproduce
themselves by the union of two endochromes. They are very interesting
objects under the microscope, owing to the spiral or zigzag
arrangement of the endochrome of many of them, and the delicacy of
all.
The Bulbochaeteae constitute a small group, some half-a-dozen species
being British. They are freshwater plants, composed of articulate
branched filaments, with fertile bulbshaped branchlets. The endochrome
is believed to be fertilized by bodies developed in antheridia, the
contents of each fertilized cell dividing into four ovate zoospores.
The last two groups of green sea-weeds consist chiefly of marine
plants. Of these the first, Siphoneae, is so called because the plant,
however complicated, is composed invariably of a single cell. It
propagates by minute zoospores, by large quiescent spores, or by large
active spores clothed with cilia. It includes the remarkable genus
Codium, three species of which inhabit the British seas. In Codium
Bursa the filamentous frond is spherical and hollow, presenting more
the appearance of a round sponge or puff-ball than a sea-weed, and is
somewhat rare. Another species greatly resembles a branched sponge,
and the third forms a velvety crust on the surface of rocks. Another
genus, Vaucheria, is of a beautiful green colour, forming a velvety
surface on moist soil, on mud-covered rocks overflowed by the tide, or
parasitic on other sea-weeds. The most attractive plants of this
family are however those of the genus Bryopsis, two of which are found
on the British shores. The most common one is B. plumosa, the fronds
of which grow usually in the shady and sheltered sides of rock pools.
The fronds of the last of the green-weed groups, the Ulvaceae, are
membranous, and either flat or tubular. Two of them, Ulva latissima,
the green, and Porphyra laciniata, the purple laver, are among the
most common sea-weeds, growing well up from low-water mark. The
propagation in all of them is by zoospores. An allied genus,
Enteromorpha, is protean in its forms, which have been classed under
many species. They may, however, be reduced to half a dozen. Some of
them are very slender, so as almost to be mistaken for confervoid
plants.
With the Rhodospermeae we enter a sub-order of Algae, exclusively
marine, the plants in which have always held out great attractions to
the collector. In structure they are expanded or filamentous, nearly
always rose-coloured or purple in colour. Of the fourteen groups into
which they are divided by Harvey, the first is Ceramiaceae, articulate
Algae, constituting a large proportion of the marine plants of our
shores. Of the genus Ceramium, C. rubrum is the most frequent, and it
is found in every latitude, almost from pole to pole. It is very
variable in aspect, but can always be recognized by its fruit. C.
diaphanum is a very handsome species, growing often in rock pools
along with the other. There are about fifteen native species
altogether, some of them rare, and all very beautiful, both as
displayed on paper and seen under the microscope. Crouania attenuata
is a beautiful plant, parasitic upon a Cladostephus or Corallina
officinalis. It is however extremely rare, being only found in England
about Land's End. A more common and conspicuous, but equally handsome
plant is Ptilota plumosa (Fig. 9), which is mostly confined to our
northern coasts; although P. sericea, a smaller species, or variety,
is common in the south, and easily distinguished from its congener,
which it otherwise greatly resembles, by its jointed branchlets and
pinnules. Callithamnion, Halurus and Griffithsia, articulate like
Ceramium, furnish also several handsome species. (Fig. 5.)
[Illustration: Fig. 5. Species of Callithamnion.]
The group Spyridiaceae contains only one English plant, Spyridia
filamentosa, which is curiously and irregularly branched, the branches
being articulate and of a pinky red. One of its kinds of fruit,
consisting of crimson spores, is contained in a transparent network
basket, formed by the favellae, or short branches, whence its name.
[Illustration: Fig. 6. Chondrus crispus.]
The Cryptonemiaceae are very numerous in genera and species. They all
have inarticulate branches, some are thread-like. Grateloupia filicina
is a neat little plant, met with rarely on the south and west coasts.
Gigartina mamillosa, a common plant everywhere, is the plant sold,
along with Chondrus crispus, as Irish or Carrageen moss. A handsome
little plant, Stenogramme interrupta, is very rare, but it has been
gathered both on the Irish and English coasts. The Phyllophorae, one
species of which is frequent on all our shores, may be recognised by
the way in which the points and surfaces of their fronds throw out
proliferous leaves. Gymnogongrus has two British species, one much
resembling Chondrus crispus, already named, of which it was formerly
considered a congener. Their fructification is however very different.
Ahnfeltia plicata is a curiouswiry, entangled plant, almost black in
colour, and like horse-hair when dry, and can scarcely be mistaken.
Cystoclonium purpurascens is very commonly cast up by the tide on most
of our coasts. It varies in colour, but is easily distinguished by the
spore-bearing tubercles imbedded in its slender branches. Callophyllis
laciniata is a handsome species, of a rich crimson colour, and
sometimes a foot square. It can scarcely have escaped the notice of
the sea-side visitor, for it is widely distributed and often thrown
out in great abundance; one writer describes the shore near Tynemouth
as having been red for upwards of a mile with this superb sea-weed.
Kalymenia reniformis is another of the broad, flat Algae, but it is
scarcer, and of a colour not so conspicuous. Among the most frequent
of our sea-weeds, both as growing in the rock pools and cast ashore,
is Chondrus crispus, already twice referred to in connexion with its
officinal uses. It is very variable in form, one author figuring as
many as thirty-six different varieties. (Fig. 6.) Chylocladia
clavellosa, which is sometimes cast ashore a foot and a half long, is
closely set with branches, and these again clothed with branchlets in
one or two series. The whole plant is fleshy, of a rose-red or
brilliant pink colour, turning to golden yellow in decay. There is
another small species, confined to the extreme north of Britain.
Halymenia ligulata is another flat red weed, but sometimes very narrow
in its ramifications. Furcellaria fastigiata has a round, branched,
taper stem, swollen at the summit, which contains the fruit,
consisting of masses of tetraspores in a pod-like receptacle.
Schizymenia edulis, better known perhaps by its old name Iridea, is a
flat, inversely egg-shaped leaf with scarcely any stem. It is one of
the edible Algae, and pretty frequent in shady rock pools.
Gloiosiphonia capillaris is a remarkably beautiful plant, and not
common, being confined to certain parts of the southern coasts. The
stem is very soft and gelatinous; the spores are produced in red
globular masses imbedded in the marginal filaments, which have a fine
appearance under the microscope when fresh.
[Illustration: Fig. 7. Rhodomenia palmata.]
[Illustration: Fig. 8. Wormskioldia sanguinea.]
The Rhodomeniaceae are purplish or blood-red sea-weeds, inarticulate,
membranaceous, and cellular. Among the dark-coloured is Rhodomenia
palmata, better known as dulse, a common and edible species. (Fig. 7.)
Wormskioldia sanguinea is not only the most beautiful sea-weed, but
the finest of all leaves or fronds. It is usually about six inches
long, but sometimes nearly double that length and six inches broad,
with a distinct midrib and branching veins, and a delicate wavy
lamina, pink or deep red. The fruit is produced in winter from small
leaflets growing upon the bare midrib. (Fig. 8.) The commonest of all
red sea-weeds on our coast, one of the most elegant, and much sought
after by sea-weed picture makers, Plocamium coccineum, belongs to this
group. Calliblepharis ciliata and jubata are coarser plants, the
latter being the more frequent. They were formerly included in the
genus Rhodymenia, from which they were removed when their fruit was
better understood.
[Illustration: Fig. 9. Ptilota plumosa.]
Wrangelia and Naccaria are the only British genera in Wrangeliaceae.
There is only one native species in each, both being rare, the latter
especially.
The Helminthocladiae are also a limited group, of a gelatinous
structure; so much so that on being gathered they feel like a bunch of
slimy worms, whence the name of the family. Helminthora purpurea and
divaricata with Nemaleon multifidum and Scinaia furcellata represent
them in Britain. They are nearly all very rare, pretty plants, and
very effective as microscopic objects.
The Squamariae, formerly included in the Corallinaceae, are a small
group of inconspicuous plants resembling lichens, of a leathery
texture, and growing on rocks and shells attached by their lower
surface.
A single genus only, Polyides, represents the Spongiocarpeae. Polyides
rotundus resembles Furcellaria fastigiata very closely, but differs
widely in the fruit, which consists of spongy warts surrounding the
frond, composed of spores and articulated threads.
Of the next group represented in Britain, Gelidiaceae, we have only one
plant, Gelidium corneum, very common on our shores, and perhaps the
most variable of all vegetable species.
The Sphaerococcidae include both membranaceous and cartilaginous
species. Of the latter is Sphaerococcus coronopifolius, which cannot
easily be mistaken, owing to the numerous berry-like fruits that tip
its branchlets. It is rather rare on the northern, but often thrown
ashore in large quantities on the southern coasts. The genus
Delesseria has four British species, the largest being the well-known
D. sinuosa, the fronds of which resemble an oak leaf in outline. The
handsomest are D. ruscifolia and D. hypoglossum, which are more
delicate and of a finer colour than sinuosa. There are three British
species of Gracillaria, in two of which the branches are cylindrical,
and in the other flat. G. compressa makes an excellent preserve and
pickle, but unfortunately it is the rarest of the three. Nitophyllum
is one of the greatest ornaments of this tribe. There are six British
species, which are amongst the most delicate and beautiful of our
native Algae.
The Corallinaceae are remarkable for the property they possess of
absorbing carbonate of lime into their tissues, so that they appear as
a succession of chalky articulations or incrustations. The most common
is Corallina officinalis. There are two British species of Corallina,
and two also of the nearly allied genus, Jania. Of the foliaceous
group there are likewise two British genera, Melobesia and
Hildenbrantia.
The next group, the Laurenciaceae, are cartilaginous and cylindrical or
compressed, the frond in the greater portion of them being
inarticulate and solid. They contain several species valued by
collectors, although some of them are amongst our commonest plants.
Their colour is, when perfect, a dull purple or brownish red, but they
change under the influence of light and air, while fresh water is
rapidly destructive to their tints. (Fig. 10.)
[Illustration: Fig. 10. Laurencia pinnatifida.]
The Chylocladiae are curiously jointed plants, removed by Agardh to a
new genus, Lomentaria, and a new order Chondriae. Bonnemaisonia
asparagoides is the most rare and beautiful of the tribe.
The last tribe of red weeds, Rhodomelaceae, varies greatly in the
structure of the frond, but the fruit is more uniform. Polysiphonia
and Dasya contain the finest of the filiform division; the leafy one,
Odonthalia, a northern form, is a very beautiful sea-weed both as
respects form and colour. Well-grown specimens are not unlike a
hawthorn twig, and of a blood red colour.
The plants of the sub-order Melanospermeae, are, like the red
sea-weeds, exclusively marine. They are usually large and coarse, and
confined mostly to comparatively shallow water. In the Laminariaceae we
find the gigantic oarweeds already briefly referred to. Lessonia,
which encircles in submarine forests the antarctic coasts, is an
erect, tree-like plant, with a trunk from five to ten feet high,
forked branches, and drooping leaves, one to three feet in length, and
has been compared to a weeping willow. Sir Joseph Hooker says, that
from a boat there may on a calm day be witnessed in the antarctic
regions, over these submarine groves, "as busy a scene as is presented
by the coral reefs of the tropics. The leaves of the Lessoniae are
crowded with Sertulariae and Mollusca, or encircled with Flustra; on
the trunks parasitic Algae abound, together with chitons, limpets, and
other shells; at the base and among the tangled roots swarm thousands
of Crustaceae and Radiata, while fish of several species dart among the
leaves and branches." Of these and other gigantic melanosperms, flung
ashore by the waves, a belt of decaying vegetable matter is formed,
miles in extent, some yards broad, and three feet in depth; and Sir J.
Hooker adds that the trunks of Lessonia so much resemble driftwood
that no persuasion could prevent an ignorant shipmaster from employing
his crew, during two bitterly cold days, in collecting this
incombustible material for fuel. Macrocystis and Nereocystis are also
giant members of this sub-order. Some of the Laminariae which form a
belt around our own coasts not seldom attain a length of from eight to
twelve feet. The common bladder-wrack (Fucus vesiculosus) sometimes
grows in Jutland to a height of ten feet, and in clusters several feet
in diameter. The colour of most of the plants in this sub-order is
some shade of olive, but several of them turn to green in drying.
The first group, Ectocarpeae, is composed of thread-like jointed
plants, the fructification of which consists of external spores,
sometimes formed by the swelling of a branchlet. The typical genus,
Ectocarpus, abounds in species, a dozen or so of which, very nearly
allied plants, being found around our own shores. One or two of them
are very handsome. There are also some very beautiful plants in the
genus Sphacelaria, belonging to this group, several of them resembling
miniature ferns. All the Sphacelariae are easily recognized by the
withered appearance of the tips of the fruiting branches. Myriotrichia
is a genus of small parasitical plants, the two British species of
which grow chiefly on the sea thongs (Chorda).
The Chordariae are sometimes gelatinous in structure, in other cases
cartilaginous. The fruit is contained in the substance of the frond.
The genus Chordaria consists of plants which have the appearance of
dark coloured twine. There are two British species, one being rather
common. Chorda filum, sea-rope, another string-like sea-weed, grows in
tufts from a few inches to many feet in length, and tapering at the
roots to about the thickness of a pig's bristle. In quiet land-locked
bays with a sandy or muddy bottom, it sometimes extends to forty feet
in length, forming extensive meadows, obstructing the passage of
boats, and endangering the lives of swimmers entangled in its slimy
cords, whence probably its other name of "dead men's lines."
[Illustration: Fig. 11. Padina pavonia.]
The Mesogloieae in a fresh state resemble bundles of green, slimy
worms. There are three British species, two of which are not uncommon.
Although so unattractive in external aspect, they, like many others of
the same description, prove very interesting under the microscope. One
of the cartilaginous species, Leathsia tuberiformis, has the
appearance, when growing, of a mass of distorted tubers.
The species of Elachista, composed of minute parasites, are, as well
as unattractive like the Mesogloieae, inconspicuous, but are beautiful
objects when placed under the microscope. Myrionemae are also
parasitic, and even smaller than the plants of the preceding genus.
In the Dictyoteae the frond is mostly flat, with a reticulated surface,
which is sprinkled when in fruit with groups of naked spores or spore
cysts. This tribe includes not a few of the most elegant among the
Algae. In structure they are coriaceous, and include plants both with
broad and narrow, branched and unbranched fronds. In Haliseris there
is a distinct midrib. The largest of the British Dictyoteae is Cutleria
multifida, sometimes found a foot and a half long; and the best known
is doubtless Padina pavonia, much sought after by seaside visitors
where it grows. Its segments are fan-shaped, variegated with lighter
curved lines, and fringed with golden tinted filaments. (Fig. 11.)
Owing to its power of decomposing light, its fronds, when growing
under water, suggest the train of the peacock, whence its specific
name. Taonia atomaria somewhat resembles Cutleria, but exhibits also
the wavy lines of Padina. The plant of this group most often cast
ashore is Dictyota dichotoma. It makes a handsome specimen when well
dried, and is interesting on account of the manner in which it varies
in the breadth of its divisions. The variety intricata is curiously
curled and entangled. Dictyosiphon foeniculaceus, the solitary
British example of its genus, is a bushy filiform plant, remarkable
for the beautiful net-like markings of its surface. The Punctariae have
flattened fronds, marked with dots, which sufficiently distinguish
them from all the others. A small form is often found parasitic on
Chorda filum, spreading out horizontally like the hairs of a bottle
brush. Asperococcus derives its name from its roughened surface,
occasioned by the thickly scattered spots of fructification.
The Laminariaceae are inarticulate, mostly flat, often strap-shaped.
Their spores occur in superficial patches, or covering the whole
frond. The plants of this order, as we have already seen, include the
giants of submarine vegetation. In point of mass they constitute the
larger part of our native Algae, although they number only a few
species. They are popularly known as tangle or oarweeds, and the stems
of Laminaria saccharina and the midrib of Alaria esculenta are used as
food.
The Sporochnaceae are a small but beautiful tribe, inarticulate, and
producing their spores in jointed filaments or knob-like masses, and
remarkable for their property of turning from olive brown to a
verdigris green when exposed to the atmosphere.
[Illustration: Fig. 12. Fucus serratus, showing a transverse
section of the Conceptacle, and Antheridium with Antherozoids
escaping.]
They are deep sea plants, or at least grow about low water mark. The
largest of the group is Desmarestia ligulata, which, with the other
British species, D. aculeata, is often cast ashore. The latter
species, at an early period of its existence, is clothed with tufts of
slender hairs, springing from the margin of the frond. Desmarestia
viridis is the most delicate and also the rarest of the three. Nothing
like fruit has been discovered on any of them. Arthocladia villosa and
Sporochnus pedunculatus are branched sea-weeds, covered also with
tufts of closely set hairs. Carpomitra Cabrerae, a rare species, bears,
in common with the two preceding species, its spores in a special
receptacle. In the first the receptacle is pod-like; in the second
knotted; and in the last mitriform.
The concluding group of Algae is the Fucaceae, including the universally
known sea wrack (Fucus). The frond in all of them is jointless. They
are reproduced by means of antheridia and oogonia developed in
conceptacles, clustered together at the apex of the branches. Both
from their bulk and their decided sexual distinctions, they deserve to
rank at the head of the order. Of all sea-weeds they are also perhaps
of the greatest use to man. One of the most interesting among them is
the Gulfweed (Sargassum bacciferum), occupying a tract of the Atlantic
extending over many degrees of latitude. Pieces of it, and of its
congener, S. vulgare, are occasionally drifted to our shores, and they
consequently find a place in works on British Algae, although they have
no claim to be considered native plants. On rocky coasts the various
species of Fucus occupy the greater part of the space between
tide-marks, the most plentiful being Fucus vesiculosus. F. serratus
(Fig. 12) is the handsomest of the genus, the other species being F.
nodosus, said to be the most useful for making kelp, and F.
canaliculatus. Halidrys siliquosa is remarkable for its spore
receptacles, which have quite the appearance of the seed vessel of a
flowering plant. The species of Cystoseira, chiefly confined to the
southern coasts, are also very interesting. Their submerged fronds are
beautifully iridescent, and the stems, of the largest species at
least, are generally covered with a great variety of parasites, animal
and vegetable, the former consisting of Hydrozoa and Polyzoa, and
other curious forms. Himanthalia lorea is another remarkable plant. It
has conspicuous forked fruit-bearing receptacles; but the real plants
are the small cones at the base of these, and from which they are shed
when ripe.
As to conditions of site and geographical distribution, Algae do not
differ from land plants. Latitude, depth of water, and currents
influence them in the same way as latitude, elevation, and station
operate on the latter; and the analogy is maintained in the almost
cosmopolitan range of some, and the restricted habitat of others. Not
many extra-European species of Desmids are known, but those of Diatoms
are far more widely diffused, and extend beyond the limits of all
other vegetation, existing wherever there is water sufficient to allow
of their production; and they are found not only in water, but also
on the moist surface of the ground and on other plants, in hot springs
and amid polar ice. They are said to occur in such countless myriads
in the South Polar Sea as to stain the berg and pack ice wherever
these are washed by the surge. A deposit of mud, chiefly consisting of
the shells of Diatoms, 400 miles long, 120 miles broad, and of unknown
thickness, was found at a depth of between 200 and 400 feet on the
flanks of Victoria Land in 70 deg. south latitude. Such is their abundance
in some rivers and estuaries that Professor Ehrenberg goes the length
of affirming that they have exercised an important influence in
blocking up harbours and diminishing the depth of channels. The trade
and other winds distribute large quantities over the earth, which may
account for the universality of their specific distribution; for Sir
Joseph Hooker found the Himalayan species to closely resemble our own.
Common British species also occur in Ceylon, Italy, Virginia, and
Peru. The typical species of the Confervaceae are also distributed over
the whole surface of the globe. They inhabit both fresh and salt
water, and are found alike in the polar seas and in the boiling
springs of Iceland, in mineral waters and in chemical solutions. Some
of the tropical ones are exceedingly large and dense. Batrachospermum
vagum, in the next tribe, a native of England, is also found in New
Zealand. An edible species of Nostochineae, produced on the boggy
slopes bordering the Arctic Ocean, is blown about by the winds
sometimes ten miles from land, where it is found lying in small
depressions in the snow upon the ice. The common Nostoc of moist
ground in England occurs also in Kerguelen's Land, high in the
southern hemisphere. Floating masses of Monormia are often the cause
of the green hue assumed by the water of ponds and lakes. Certain
species of Oscillatoria of a deep red colour live in hot springs in
India, and the Red Sea is supposed to have derived its name from a
species of this tribe, which covers it with a scum for many miles,
according to the direction of the wind. The lake of Glaslough in
County Monaghan, Ireland, owes its colour and its name to Oscillatoria
aerugescens, and large masses of water in Scotland and Switzerland are
tinted green or purple by a similar agency. A few species of Siphoneae
have a very wide range, two British species of Codium occurring in New
Zealand. The Ulvaceae abound principally in the colder latitudes.
Enteromorpha intestinalis, a common British species, is as frequent in
Japan, where it is used, when dried, in soup. The Rhodosperms are
found in every sea, although the geographical boundaries of genera are
often well-marked. Gloiosiphonia, one of our rarest and most
beautiful Algae, is widely diffused. Of Melanosperms the Laminariae
affect the higher northern latitudes, Sargassa abound in the warmer
seas, while Durvillaea, Lessonia, and Macrocystis characterize the
marine flora of the Southern Ocean. The Fucaceae are most abundant
towards the poles, where they attain their greatest size. The marine
meadows of Sargassum, conceived by some naturalists to mark the site
of the lost Atlantis, and which give its name to the Sargasso Sea,
extending between 20 deg. and 25 deg. north latitude, in 40 deg. west longitude,
occupy now the same position as when the early navigators, with
considerable trepidation, forced through their masses on the way to
the New World. Sargassum is drifted into this tract of ocean by
currents, the plants being all detached; and they do not produce fruit
in that state, being propagated by buds, which originate new branches
and leaves. (Fig. 13.)
[Illustration: Fig. 13. The Gulf-weed (Sargassum bacciforum).]
Owing to their soft, cellular structure, Algae are not likely to be
preserved in a fossil state; but what have been considered such have
been found as low down as the Silurian formation, although their
identity has been disputed, and several of them, it is more than
probable, belong to other orders, and some even to the animal kingdom.
Freshwater forms, all of existing genera and species, are believed to
have been detected in the carboniferous rocks of Britain and France;
others also of the green-coloured division are said to occur from the
Silurian to the Eocene, and the Florideae to be represented from the
Lias to the Miocene. The indestructible nature of the shells of the
Diatomaceae has enabled them to survive where the less protected
species may have perished. Tripoli stone, a Tertiary rock, is entirely
composed of the remains of microscopic plants of this tribe. It is
from their silicious shells that mineral acquires its use in the arts,
as powder for polishing stones and metals. Ehrenberg estimates that in
every cubic inch of the tripoli of Bilin, in Bohemia, there are
41,000,000 of Gaillonella distans. Districts recovered from the sea
frequently contain myriads of Diatoms, forming strata of considerable
thickness; and similar deposits occur in the ancient sites of lakes in
this and other countries.
* * * * *
Before setting out in search of Algae the collector ought to provide
himself with a pair of stout boots to guard his feet from the
sharp-pointed rocks, as well as a staff or pole to balance himself in
rock-climbing, which ought to have a hook for drawing floating weed
ashore. A stout table-knife tied to the other end will be found very
useful. A basket--a fishing-basket does very well--or a waterproof
bag, for stowing away his plants, is also necessary. It is advisable
to carry a few bottles for the very small and delicate plants, and
care should be taken to keep apart, and in sea-water, any specimens of
the Sporochnaceae; for they are not only apt to decay themselves but to
become a cause of corruption in the other weeds with which they come
in contact. These bottles should always be carried in the bag or
pocket, never in the hand.
Sea-weeds, as every visitor to the coast knows, are torn up in great
numbers by the waves, especially during storms, and afterwards left on
the shore by the retiring tide. Many shallow-growing species are also
to be found attached to the rocks, and in the rock pools, between high
and low water mark. There are three points on the beach where the
greatest accumulations of floating Algae are found: high water mark,
mid-tide level, and low water mark. Low water occurs about five or
five and a half hours after high water. The best time for the
collector to commence is half an hour or so before dead low water. He
can then work to the lowest point safely, and, retiring before the
approaching tide, examine the higher part of the beach up to high
water mark. If the coarse weeds in the rock pools and chinks are
turned back, many rare and delicate Algae will be found growing under
them, especially at the lowest level. The most effective method of
collecting the plants of deeper water is by dredging, or going round
with a boat at the extreme ebb, and taking them from the rocks and
from the Laminaria stems, on which a great number have their station.
Stems of Laminaria thrown out by the waves should also be carefully
examined. In all cases the weed should be well rinsed in a clear rock
pool before being put away in the bag or other receptacle.
The next thing to be considered is the laying out and preserving of
the specimens selected for the herbarium. Wherever possible these
should be laid out on paper, and put under pressure as soon as
gathered, or on the same day at all events. When this is
impracticable, they may be spread between the folds of soft and thick
towels and rolled up. Thus treated the most delicate plants will keep
fresh until next day. Another way is to pack the plants in layers of
salt, like herrings; but the most usual method of roughly preserving
sea-weeds collected during an unprepared visit to the shore is by
moderately drying them in an airy room out of the direct rays of the
sun. They are then to be placed lightly in bags, and afterwards
relaxed by immersion and prepared in the usual way. The finer plants,
however, suffer more or less by this delay. If carried directly home
from the sea the plants should be emptied into a vessel of sea-water.
A flat dish, about fourteen inches square and three deep, is then to
be filled with clean water. For most plants this may be fresh, for
some it is essential that it should be salt. Some of the Polysiphonias
and others begin to decompose at once if placed in fresh water. The
Griffithsias burst and let out their colouring matter, and a good many
change their colour. The appliances required are some fine white
paper--good printing demy, thirty-six pounds or so in weight per ream,
does very well,--an ample supply of smooth blotting paper, the coarse
paper used by grocers and called "sugar royal," or, best of all,
Bentall's botanical drying paper, pieces of well-washed book muslin, a
camel's hair brush, a bodkin for assisting to spread out the plants, a
pair of scissors, and a pair of forceps. The mounting paper may be cut
in three sizes: 5 in. by 4 in., 71/2 in. by 51/4 in., and 10 in. by
71/2 in. Then having selected a specimen, place it in the flat dish
referred to above, and prune it if necessary. Next take a piece of
the mounting paper of suitable size, and slip it into the water
underneath the plant, keeping hold of it with the thumb of the left
hand. Having arranged the plant in a natural manner on the paper,
brush it gently with the camel's hair brush to remove any dirt or
fragments, draw out paper and plant gently and carefully in an oblique
direction, and set them on end for a short time to drain. Having in
this way transferred as many specimens as will cover a sheet of drying
paper, lay them upon it neatly side by side, and cover them with a
piece of old muslin. Four sheets of drying paper are then to be placed
upon this, then another layer of plants and muslin and four more
sheets of drying paper, until a heap, it may be six or eight inches
thick, is built up. Place this between two flat boards, weighted with
stones, bricks, or other weights; but the pressure should be moderate
at first, otherwise the texture of the muslin may be stamped on both
paper and plant. The papers must be changed in about three hours'
time, and afterwards every twelve hours. In three or four days,
according to the state of the weather, the muslin may be removed, the
plants again transferred to dry paper, and subjected to rather severe
pressure for several days.
The very gelatinous plants require particular treatment. One way is to
put them in drying paper and under a board but to apply no other
pressure, change the drying paper at least twice during the first half
hour, and after the second change of dryers apply very gentle
pressure, increasing it until the specimens are fully dry. A safer and
less troublesome way, for the efficacy of which we can vouch, is to
lay down the plants and dry them without any pressure, afterwards
damping the back of the mounting papers and placing them in the drying
press. Some Algae will scarcely adhere to paper. These should be
pressed until tolerably dry, then be immersed in skim-milk for a
quarter of an hour, and pressed and dried as before. A slight
application of isinglass, dissolved in alcohol, to the under side of
the specimen is sometimes necessary. Before mounting, or at all events
before transference to the herbarium, care should be taken to write in
pencil on the back of the paper the name of the plant, if known, the
place where gathered, and the date. The coarse olive weeds, such as
the bladder-wrack, Halidrys, and the like, may in the case of a short
visit to the coast be allowed to dry in an airy place, and taken home
in the rough. Before pressing, in any case, they should be steeped in
boiling water for about half an hour to extract the salt, then washed
in clean fresh water, dried between coarse towels, and pressed and
dried in the same way as flowering plants. A collection of Algae may be
fastened on sheets of paper of the usual herbarium size and kept in a
cabinet or portfolios, or attached to the leaves of an album. For
scientific purposes, however, the latter is the least convenient way.
There are few objects more beautiful than many of the sea-weeds when
well preserved; but the filiform species, especially those of the
first sub-order, do not retain their distinguishing characters when
pressed as has been described. Portions of these, however, as well as
sections of stems and fruit, may be usefully dried on small squares of
thin mica, for subsequent microscopic examination, or they may be
mounted on the ordinary microscope slides. This is the only course
possible with Desmids and Diatoms. The former are to be sought in
shallow pools, especially in open boggy moors. The larger species
commonly lie in a thin gelatinous stratum at the bottom of the pools,
and by gently passing the fingers under them they will be caused to
rise towards the surface, when they can be lifted with a scoop. Other
species form a greenish or dirty cloud on the stems and leaves of
other aquatic plants, and by stripping the plant between the fingers
these also may be similarly detached and secured. If they are much
diffused through the water, they may be separated by straining through
linen; and this is a very common way of procuring them. Living Diatoms
are found on aquatic plants, on rocks and stones, under water or on
mud, presenting themselves as coloured fringes, cushion-like tufts, or
filmy strata. In colour the masses vary from a yellowish brown to
almost black. They are difficult, both when living and dead, to
separate from foreign matter; but repeated washings are effectual in
both cases, and, for the living ones, their tendency to move towards
the light may also be taken advantage of. When only the shells are
wanted for mounting, the cell contents are removed by means of
hydrochloric and nitric acid. The most satisfactory medium for
preserving fresh Desmids and Diatoms is distilled water, and if the
water is saturated with camphor, or has dissolved in it a grain of
alum and a grain of bay salt to an ounce of water, confervoid growths
will be prevented. For larger preparations of Algae, Thwaites' fluid is
strongly recommended. This is made by adding to one part of rectified
spirit as many drops of creasote as will saturate it, and then
gradually mixing with it in a pestle and mortar some prepared chalk,
with sixteen parts of water; an equal quantity of water saturated with
camphor is then to be added, and the mixture, after standing for a
few days, to be carefully filtered.
For authorities on the morphology and classification of the Algae,
students may be referred to Sachs' "Text Book" and Le Maout's "System
of Botany," of which there are good translations, and the
"Introduction to Cryptogamic Botany," by the Rev. M. J. Berkeley; for
descriptions and the identification of species, to the text and
figures of Harvey's "Phycologia Britannica," and "Nature-Printed
Sea-weeds." Both of these are however costly. Among the cheaper works
are "British Sea-weeds," by S. O. Gray (Lovell, Reeve & Co.),
"Harvey's Manual" and an abridgment by Mrs. A. Gatty, with reduced but
well executed copies of the figures, of the Phycologia. This synopsis
can often be picked up cheap at second-hand book-stalls; and there is
a very excellent low-priced work suitable for amateurs, Grattann's
"British Marine Algae," containing recognizable figures of nearly all
our native species. Landsborough's "Popular History of British
Sea-weeds," and Mrs. Lane Clarke's "Common Sea-weeds," are also cheap
and useful manuals on the subject.
[Illustration: Floral design]