SEAWEEDS.
It is to the rocky shore we must first turn our steps, if we desire to
obtain a wide acquaintance with the British Seaweeds: that is the grand
hunting ground for the Phycologist. In the rock-pools he will find very
many of the smaller species, and thickly coating the fringing rocks
are the larger, tough and leathery species of _Fucus_ and _Laminaria_,
forming at once a breakwater that largely destroys the force of heavy
seas, and a splendid cover for the soft-bodied creatures that swarm on
the rock-surface, and feed on the plants that protect them from the
fury of the waves. The ancients called them _inutiles algæ_, but in
the ocean’s ceaseless warfare with the land, the greatest obstacle the
former has to encounter is the network shield of seaweed, that breaks
the force of its heaviest blows. This is an utilitarian characteristic
of the seaweeds, for which Britons, at least, should be thankful, quite
apart from their minor importance as sources of food, physic, fodder,
and manure, and their æsthetic qualities.
The whole class of Seaweeds, with the solitary exception of the
Grass-wrack (_Zostera maritima_) belong to the flowerless division of
plant-life, and to that section called Algæ. They are plants of simple
organization, being innocent of wood or other complicated tissue; the
whole plant being made up of cells, though in the higher families
there is an approach to the formation of vessels and tissues. They are
absolutely without roots, though the larger species are attached to
rocks or other algæ, by what appears to be a root. This organ, however,
does not penetrate into the substance to which it is attached, but is
a mere sucker, sticking tightly to the surface, and taking no part in
the absorption of food for the plant, which is effected by the entire
general surface of the frond from the surrounding waters, in which it
floats in a more or less erect attitude, but yielding to every movement
of the sea.
The seaweeds are all reproduced by spores, but the structure and
production of these differ in the different groups, some being asexual,
and others the result of a distinct sexual process. To this matter we
shall give further attention by and by.
[Illustration: CHANNELLED WRACK.]
The most striking seaweeds owing to their size and abundance are those
comprised in the _Fucaceæ_, all the species of which are olive-brown
in colour. There are four species of Fucus which are very abundant on
our shores, as well as representatives of other genera included in
the family. On the highest of the rocks, that only become covered by
high spring-tides, and are only washed by rough seas, there grows in
abundance a little leathery plant called the Channelled Wrack (_Fucus
canaliculatus_). During the greater part of its existence it is dry and
shrivelled and of black hue, but when covered by the tide it absorbs
the water, and becomes soft, with an olive-brown tint. The frond is
much branched, the segments long and narrow, the edges being turned
in so that on one side they appear to be deeply channelled. It is
the smallest of our species of _Fucus_, and is readily distinguished
from its congeners, not only by its size, but by the channel-like
folding, the absence of air bladders, and the lack of a mid-rib. At
the extremity of some of its fronds there are irregular warty pod-like
organs of a dark orange tint. These are known as the _receptacles_,
and they contain the elements necessary for the production of spores,
whereby the plant is reproduced. In one plant these elements will be
all male (_antherids_), in another all female (_oogones_). If you will
examine one of these club-shaped orange organs with your pocket lens,
you will observe that its surface is pitted with a considerable number
of round pores, and if you cut across the whole body just on the edge
of one of these pores, you will find it communicates with a globular
cell in the substance of the receptacle. These cells are known as
_conceptacles_, and their number corresponds to that of the pores.
Their walls are clothed with a felt-work of threads, upon which are
borne, in the male conceptacles, minute egg-shaped cells (_antherids_),
which ultimately burst, and set free thirty-two or sixty-four
tadpole-like bodies (_antherozoids_), each with two tail-like threads
(_cilia_) attached to the under part. By the lashing of these organs
they make their way out through the pore of the receptacle into the sea.
With the development of the antherozoids, a similar activity has taken
place in the female conceptacles, where bodies approaching more to an
ellipsoidal or spherical form (_oogones_) have appeared, and their
contents have broken up into two, four, or eight smaller bodies (the
_oospheres_). On their escape into the water, they are each surrounded
by a number of the antherozoids, which pierce the substance of the
oosphere, become absorbed in it, and so fertilise it. Development then
commences in the oosphere, and it gives rise to a new _Fucus_ plant.
This form of reproduction is by no means common to the whole class of
seaweeds; on the contrary, there are many important variations of it,
which for want of space we shall be unable to refer to in detail. This
is the highest type of reproduction in the Algæ.
The Channelled Wrack never exceeds a few inches in length, but another
species, which agrees with it to the extent of possessing no mid-rib,
varies from two to six feet. This is the Knotted Wrack (_Fucus
nodosus_), which may be at once identified by the possession of
solitary bladders in the centre of its rib-less frond, and producing
a very gouty appearance at intervals. These are air-cells, sometimes
measuring two inches, which give buoyancy to the plant. Above the
bladders the frond divides, and from these branches (but not at their
extremities, as in the Channelled Wrack) the pear-shaped reproductive
organs are produced.
[Illustration: BLADDER WRACK.]
Another Wrack that possesses these vesicles, is the so-called Bladder
Wrack or Black Tang (_Fucus vesiculosus_), though there is little
danger of confusing the two species. The Bladder Wrack has a much
broader, flatter frond than the Knotted Wrack, and a very distinct
mid-rib. The bladders, too, are smaller, and instead of being solitary,
are arranged in groups on each side of the mid-rib. The plant is about
two feet in length, and exceedingly plentiful.
[Illustration: SAW-EDGED WRACK.]
Very similar, and equally plentiful, is the Saw-edged Wrack (_Fucus
serratus_), with flat, branched fronds and mid-rib, the branches much
broader than in Bladder Wrack, and the edges cut into bold, sharp,
distant teeth. Its usual length is from two to three feet, but it may
occur as long as five or six feet. The width of frond also varies, for
it may be anything between half an inch and two inches. Where the
frond branches the mid-rib becomes thicker and bolder. It is quite
innocent of bladders. The name of the genus is founded upon the word
_Phukos_, which is the Greek name for a seaweed.
[Illustration: POD-WEED.]
Almost equally plentiful with those species of _Fucus_ we have
named, is the Pod-weed (_Halidrys siliquosa_), with long attenuated
compressed fronds, four or five feet in length, much branched, most of
the branches being exceeding short, but others ending in air vessels.
These are ribbed transversely, and bear a very close likeness to the
seed-pods of the furze. They run out to a narrow point at the free end,
and are divided into small air-chambers within. But there are other
pods that contain the reproductive elements, and these may be known by
the pores by which their surfaces are perforated. The name _Halidrys_,
signifies sea oak (Greek, _Hals_, the sea, and _drus_, oak), but
the why and wherefore of the name are not easily determined. If the
abundant pod-like vessels are kept in mind, there is no difficulty in
knowing this species the first time it is seen.
At low-water, you will often find, attached to the rocks, a shallow
horny cup, or button, of olive hue, about the size of a penny. This is
the Sea-thongs (_Himanthalia lorea_), which gets its name from a very
long, branched, strap-like growth from the centre of the cup. The cup
is the frond--the plant proper--and the extraordinary straps, which may
be half an inch wide and twenty feet long, are merely the receptacles
containing the reproductive organs, which open by pores all over their
surfaces. The receptacles are not produced until the second year of
the plant’s life, so that many examples will be met consisting of the
cup-like frond only. It is a local plant, and not therefore to be found
on all parts of the coast.
In the lower series of tide-pools, a tufted weed attracts the sight
by reason of its brilliant iridescence, which often causes it to be
plucked from its native pool, only to be thrown back again, for on
emergence from the water all the beautiful play of colour has gone.
It does not appear to have any common name, but to give it a chance
of being popularly known, let us call it the Rainbow Bladder-weed
(_Cystoseira ericoides_). The many branches of its frond are full of
little bladders, whence its scientific name (_Kystos_, a bladder;
_seira_, a cord), and it gets its specific title of _ericoides_ from
its habit somewhat resembling that of the Heath-plant (_Erica_). A
tuft pulled up and carefully overhauled will afford the zoologist a
number of diverse forms of life. Several species of crustacea make it
their home, and the leaf-worms hide themselves in the centre of the
little bush. Mollusks, sponges, and ascidians are there also, and the
description of the animal inhabitants of such a tuft would make a fair
chapter.
All the species of seaweeds to which we have already referred, are
members of the class Fucaceæ. We have now to take a glance at other
brown and olive weeds, some of which are the giants of the tribe, but
which belong properly to the deeper waters, though every gale will
make us well acquainted with their forms heaped up upon the shore. In
this class--known to botanists as the Phæosporeæ--the reproduction is
generally of a lower type than in those we have been considering. In
the majority of forms there is no sexual process, the species being
reproduced, as a rule, by zoospores, which are somewhat similar to
the antherozoids of _Fucus_. They are produced in special cells, the
contents of which break up into a number of these zoospores, which
escape through a pore, and germinate.
Getting down into a drang at extreme low spring-tide, we shall find
the rocks to seaward covered with Tangle (_Laminaria digitata_), whose
huge round stems clasp the rocks with their claw-like false roots.
The leafy portion is broad, of a pale olive-brown, and slit up into
several sections, so that the whole frond has a rough resemblance
to the diverging fingers of a huge hand: hence its name, _digitata_
(having fingers). The substance of the frond is thick and leathery. A
species with undivided glossy narrower fronds, puckered and frilled,
is the Sugar Tangle (_Laminaria saccharina_), so-called because, when
drying, it produces on its surface a white powder of a sweet taste,
called _mannite_, or manna. This substance can also be obtained from
the cells by maceration. Subsequent evaporation of the brew results in
a deposit of crystals. This is the species that inland trippers carry
away on their visit to the coast to act as a hygrometer, hanging it on
a nail, and feeling it from time to time to find if it is dry and hard,
or moist and pliable, for its cells readily absorb moisture from the
atmosphere, and as readily part with it when the air is again dry and
clear.
A third species is called the Sea Furbelows (_L. bulbosa_), and it may
often be found washed up in great heaps after a storm. It springs from
a great hollow sphere, which is perforated, and thus affords a home for
many creatures. This so-called bulb is sometimes a foot across, and
from its stem there is a great expanse of thin leather split up into
many broad ribbons. These three species, with the larger _Fuci_, are
largely used by farmers near rocky coasts for manuring their fields,
and in former days, more widely than now, they were employed in the
manufacture of “kelp” and iodine. These Laminarians have the curious
habit of casting off the _lamina_ or blade of the frond each year, by
a constriction above the stem, whence a new one grows. This, too, it
should be stated, is the growing point, the blade increasing in length
by additions near the stem, instead of by the lengthening of the free
end. The spores are produced in large patches upon the surface of the
frond.
The Badderlocks or Murlins (_Alaria esculenta_) of our northern coasts,
belongs to this group, but is distinguished from the _Laminaria_ by
the possession of a mid-rib or central nerve. The stem is short and
cylindrical, and the blade of the frond ranges from three to twenty
feet in length, usually much torn by the waves. There are a number
of finger-like receptacles given off by the stem, and in the outer
coats of these are the conceptacles bearing the spores. The plant is
used as food by the poorer classes resident on the shores where it
is plentiful, and is eaten raw, when it is said to be the best of
our esculent seaweeds; the parts preferred are the mid-rib and the
receptacles. “Badderlocks” is a corruption of Balder’s locks, the split
fronds being likened to the locks of the Scandinavian hero Balder, to
whom all plants except mistletoe swore fealty.
To this class also belongs the slender and very extensive Sea Lace
(_Chorda filum_), which consists of a rounded frond, hollow, and
without branches. It is remarkable how tenacious the thong-like, slimy
fronds are, and it is not difficult to imagine the difficulties of a
swimmer who should have to force his way through a bed of them. The
tubular interior is divided up into a number of cells by transverse
partitions; and the spores are embedded in the outer surface. It
prefers a sandy or muddy bottom in creeks and harbours, and in such
places it grows in dense patches, the fronds attaining a length of from
twenty to forty feet. The free end is constantly dying off, but the
plant increases by growth at the lower end, just above the false roots.
The Fennel-leaved Netweed (_Dictyosiphon fœniculaceus_) is abundant in
rock-pools all round our coast. As its name implies, the frond is much
branched and thread-like. It is a light olive in colour, and grows in
tufts on stones and larger weeds. The arrangement of the cells in the
walls of the frond produce a net-like appearance.
Everyone knows the thin flat transparent fronds of Sea Lettuce (_Ulva
latissima_), which grows everywhere on the coasts, its margins
crisped, folded, torn, or otherwise diversified by Nature, or the many
things that feed upon it. It is mentioned out of its place here,
in order that we may bring into its proper order a plant that is
frequently taken as a mere aberration of the _Ulva_. This weed is the
_Asperococcus turneri_, a hollow green bladder on a short stalk, and
rough with the spore-bearing organs. It is commonly found adhering to
stones between tide-marks.
[Illustration: PEACOCK’S TAIL.]
One of the most beautiful of our seaweeds is known as the
Peacock’s Tail (_Padina pavonia_). It is really a tropical species, but
its range of distribution extends to our most southern shores, and,
strange to say, without suffering any deterioration in its brilliance
of hue or its stature. From a very narrow base the frond gradually
expands to a broad fan-shape, and the edges are curled in so that it
assumes a cup-shape. But the chief beauty of the plant is given by
a number of concentric lines and bands. Several of these bands are
white, as though they had been chalked: their colour is in fact due to
a chalky powder, _calcium carbonate_, which is secreted by the plant.
Many of the lines are formed by a fringe of glistening hairs, which
reflect the light and break it up into all the colours of the spectrum,
and a more distinct fringe decorates the upper margin of the frond.
Reproduction takes place by the formation of large spores, which are
found in heaps between the zones. These are known as _tetraspores_,
because the contents break up into four smaller spores. Sometimes this
weed is what botanists term _proliferous_, that is, it produces new
plants upon its frond. Like all those showing iridescence, it is a
much more beautiful species in the water than in the herbarium; though
it is not without beauty there, and it is a prize eagerly sought by
collectors.
It is worthy of note that fresh-water Algæ are, with very few
exceptions, green, whilst few of the marine species are truly green;
brown and olive, and red, are the prevailing hues. The green marine
weeds are nearly all found in shallow water. Of course, they all
possess the green colouring matter called _chlorophyll_, but in the
deep-water species, according to Murray and Bennett, “it appears to
be essential ... that the green colour of the chlorophyll should be
masked by a coloured pigment, red in the case of the Florideæ, brown
in those of the Phæosporeæ and Fucaceæ.” It is from these latter
classes our examples have been already drawn; we must now give a turn
to the Florideæ, which contains many of the most popularly sought
species, because they are often so charmingly tinted and so delicate in
structure.
It must not be supposed from the foregoing remarks that the whole of
this class are red weeds; the majority are not only red but brilliant
red; whilst others are purple, brown, yellowish, or dirty-white. They
are chiefly small weeds, but they make up for the want of stature in
their delicacy of texture and fineness of division.
A very beautiful genus of delicate red and purple weeds, chiefly
growing upon the larger and coarser kinds, is called _Callithamnion_
(Greek, _Kalli_, beautiful, and _thamnos_, shrub). Some attain the
length of half a foot, but most of them are much smaller. They require
careful examination with lens or microscope to decide the species, and
oftentimes in order to distinguish them from other finely branched
red weeds. For their proper discrimination we advise reference to
a book devoted exclusively to Seaweeds, such as Landsborough’s,
Gray’s, or the splendid “Phycologia Britannica” of Harvey. The general
characters of the genus are: frond branched, often pinnate, consisting
of jointed threads, with tetraspores scattered along the branches.
Other small red seaweeds will be found, representing several
genera, but they require the assistance of coloured figures to make
descriptions interesting and useful. There is the silky _Ptilota_,
with finely divided fronds, consisting of cells alternately filled
with a pink and a transparent fluid; the rosy red _Griffithsia_, with
thread-like fronds and clear transparent joints; the forking threads
of _Ceramium_, their tips curled in towards each other; the exquisite
_Plocamium_, with its flat crimson, hair-like branches, toothed on one
side only.
The Coralline (_Corallina officinalis_) grows in every pool, and its
stony-coated joints are well-known, though it is a shock to some
persons to find it classed among plants, when they had long imagined
it to be related to the corals of which necklaces and islands are
constructed. There are, in fact, several genera whose members secrete
carbonate of lime, and so hide their vegetable character. The coralline
was, however, once soft and flexible. _Melobesia_ is equally stony,
but grows in thin horizontal pink and purple plates or solid masses.
A little weak muriatic acid will soon dissolve the lime, and reveal
its true character. _Jania_ somewhat resembles _Corallina_, but its
branches are exceedingly slender, and much shorter than _Corallina_.
Among the larger red weeds that will attract attention at low-water, is
the coarse textured _Halymenia ligulata_, of dark crimson hue, whose
strap-shaped fronds support other straps by very slender attachments.
It is closely related to _Rhodymenia palmata_, a very common red
seaweed, that is eaten in Scotland, Ireland, and on the West coast
of England, under the name of Dulse or Dillisk, though it is said to
be a not very desirable food when anything else is to be obtained.
Its fronds are roughly fan-shaped, consisting of a great number of
radiating ribbon-like lobes, of a purple colour. Its texture is like
that of parchment. It will be found parasitic upon the stems of _Fucus_
and _Laminaria_, at very low-water. A more slender and ragged, thin
textured species is _Rhodymenia jubata_ with irregular outgrowths all
along its edge, some of these fringes developing into long lobes.
Another species that is also eaten as Dulse is the _Iridea edulis_,
which glitters with bluish iridescence when immersed. It has fronds
about six or seven inches long, expanding into a broad oval at the free
end, and thinning off to a wedge-shape at the base. It is represented
in the illustration of the Prawn, on page 163.
The Pepper Dulse (_Laurencia pinnatifida_) is a much smaller species,
that grows abundantly in the pools and the rocks around them, standing
the repeated scorching-up when the tide withdraws, as well as does
the Channelled Fucus, its companion. It roughly resembles a miniature
Polypody fern, but of a purple colour.
[Illustration: CHONDRUS CRISPUS.]
Another edible weed is the well-known Irish Moss or Carrageen
(_Chondrus crispus_), which was in such favour years ago as an
invalid’s food. It is well shown in the illustration, but is subject
to great variation, especially as regards colour, ranging from
greenish-white, and yellow, to a dull purple. In some of its forms
it closely resembles _Gigartina mamillosa_, to which it is not very
distantly related, and the danger of confusing the two is increased by
_Gigartina_ often growing amongst _Chondrus_. The tips of _Gigartina’s_
frond, however, are usually broader than those of _Chondrus_, and
the frond is rough, with little tubercles like grape-stones (Greek,
_gigarton_), which contain the spores. The usually purplish fronds will
be found, on cutting them across, to be not solid, as they appear, but
composed of delicate threads, in a firm clear jelly.
A pretty little red weed, that is abundant in the rock-pools, growing
upon other weeds, is the _Chylocladia parvula_, which has swollen,
cactus-like ovate joints, of a clear red, appearing as though they were
skins filled with liquid. It is allied to _Plocamium_ and _Rhodymenia_.
[Illustration: ASH-LEAVED SEA-WEED.]
The most striking of all these red-spored algæ, at least, so far as
the British flora is concerned, is the (for a seaweed) extraordinary
Ash-leaved Seaweed (_Wormskioldia sanguinea_), whose frond has a
distinct leaf-like form, with a mid-rib and branching nervures. Its
texture is so very thin, that in spite of its beautiful rosy tint, if a
specimen were laid upon this page, the print could be read through it.
Its margins are more lax than the mid-rib, so that when mounted for the
herbarium, the edges show many foldings over. The plant was formerly
placed in the genus _Delesseria_, but is now separated on account of
important differences in the matter of propagation. In this species
minute leaf-like organs spring from the mid-rib, and may be taken for
young plants springing from the parent, but these are really the bodies
that bear the spores.
The Winged Delesseria (_Delesseria alata_) is a finely and intricately
branched plant, of a rich dark crimson colour, with a suggestion of a
mid-rib, along each side of which is a narrow expanse of thin membrane,
the “wings” of its popular and technical names. It occurs in thick
tufts on the stems of _Laminaria digitata_.
My space is getting rapidly used up, though I have only been able to
mention a few of our fairly common seaweeds. There are still two or
three that I must mention. One of these is an exceedingly pretty little
form, which would be very like a soft feather that has been cast by
one of the greener varieties of the canary-bird, if it were not so
vividly green. The weed is called _Bryopsis plumosa_. It will be found
growing on the shaded walls of deep pools, and if the eye is placed
just over the edge of the pool, the Bryopsis will be found growing at
right angles with the wall, and looking so very feathery that it will
be identified at once.
Another green weed that should be mentioned is the _Enteromorpha
compressa_, of the same texture as the Sea Lettuce (_Ulva_), already
mentioned, but forming a narrow tube of rugged shape, that is
ordinarily collapsed, but sometimes inflated with oxygen gas. It is
represented in the illustration of the Sand Launce on page 275. A
tuft growing on a stone or limpet-shell, is a valuable addition to
the aquarium, for it will continue to grow, and many of the animal
inhabitants will find their food in it. Crustaceans, fishes, and
mollusks are all fond of it.
The reader who has patiently accompanied me thus far, will probably
make up his mind to preserve some of these beautiful weeds, and I
should strengthen any such intention; but let me advise that some care
be expended upon the work. Select your specimens with care, and be not
satisfied until you have, by patient seeking and overhauling, secured
fairly perfect examples with, as far as possible, the fruiting organs.
These must be carefully laid out, and gently pressed between sheets of
absorbent paper, just as in the case of flowering plants. But it should
be always remembered that the specimens as taken from the sea are more
or less coated with salt, and will never thoroughly dry until this is
removed. The first care then should be to well rinse them in clear soft
water, a few specimens at a time, to avoid leaving any for long in the
fresh water, which rapidly destroys certain species if they are left
in it for more than half an hour. Lay them out in as natural a manner
as possible, separating the delicate divisions of the frond with a
camel-hair brush. When thoroughly dry and hard, mount specimens of one
species only on the same sheet of paper, and neatly write the name of
species near the bottom left-hand corner, and near the opposite margin,
the place where, and the date when, collected.