height, with the stems not much thicker than bristles, their fronds
being long, is found on rocks near low-water mark, and generally
in deep pools from Orkney to Cornwall. It is called Griffithsia
Corallina.
Other kinds of Rhodymenia are common on rocks and stones, or on the
stems of the tangles, near the very verge of low-water, or higher
up. One found in the first situation is most common in the southwest
of England, but is found everywhere on the British shores. It has
a little disk for a root, and a long, slender stem, rather round
near the root and flat above, where it gradually expands into a red
membrane in the shape of a fan. But it is not whole, for it rather
resembles a skeleton of a fan with notches at the edges, a dark spot
being at their ends. The whole may be four inches long. The other
kind is purplish, and the stem has branches, each of which ends in a
ragged fan. It has little knobs on the side of the stem and on the
membraneous parts which bear the spores. It is sometimes called by
another generic name, that of leaf-bearer, or Phyllophora.
A rose-red sea-weed which has a midrib along all its thin branching
fronds, and which is like a flat miniature bushy tree, is common all
round British coasts, between tide-marks and more deeply. The tips of
the fronds have little bodies on them which are whiter than the rest,
and which contain peculiar spores, and there are also little knobs
or tubercles which are attached to the midrib, and these contain
another kind of spore. It belongs to a number of sea-weeds which have
been named Delesseria, after Baron Delessert, a former distinguished
botanist. Another, which is called Delesseria sanguinea, from its
blood-red, or rather rose-fed color, has a frond like a laurel-leaf,
but it is crumpled at the edges. It is thin, has a midrib, and
several spring from a stalk. Little fronds come from the midrib, in
the middle of the larger fronds. It is one of the many weeds that
fruit in winter time, and it is to be found in deep rock-pools,
between tide-marks, and generally at the shady side of the pool under
projecting ledges of rock. It is a great favorite, and grows to a
considerable size, the fronds reaching sometimes ten inches in length.
Perhaps the most beautiful of the red weeds is found on rocks, and
on other sea-weeds, at low-water mark. It resembles a number of
skeleton leaves on a stem dyed a fine red, for the frond is not a
membrane, but a number of branching threads or hairs, and it arises
from a stem. It is from six to eight inches in length, and is named
Dasya, from _dasus_, the Greek for hairy. It is much used for
ornamental purposes in the collections of sea-weeds.
One of these dissected skeleton-leaved sea-weeds is found on rocks
and on other sea-weeds, near low-water mark around British coasts.
It is a tender and soft plant of a fine carmine color, and it arises
from a stem, which, after growing for a while, branches in twos. Then
side-twigs come off opposite each other, and one on either side of
the stems and branches, and numerous hairy-looking projections arise
from the upper edge of each of the twigs. Each hairy process has
others on one side of it, and some of them bear little bulbs which
contain the spores. It is singularly regular in its growth, and, as
it is small, it looks well under low magnifying power. It is a pretty
shrub-like thing, and hence its name beautiful little shrub, or
Callithamnion. Another Callithamnion is that branching weed which is
seen waving under water upon the stems and fronds of the tangle. It
is a robust and shrubby-looking weed, which, even when dry, retains
some of its elegance of form. It is of a brownish-red color, and when
fresh water is added it becomes of a brilliant orange tint, and gives
out a rose-colored powder.
One of the many instances in which one kind of sea-weed is much more
luxurious in growth on the Irish than on the British shore is noticed
in the case of a beautiful skeleton-looking, crisp, red weed called
“Wrangelia,” after a Swedish naturalist. Its fine stem has little
whorls of fibrils one above the other, so that it presents a most
strange resemblance to the common horsetails of our marsh ground.
Branches come off from the whorls, which, horsetail fashion, have
their bracelets on successive whorls. It has a root of fibres, and
a good-sized specimen would cover a quarto page of paper. They are
found on the steep sides of pools near low-water mark, under the
shade of other sea-weeds, and they are to be picked on the south of
England, Jersey, Belfast, and the west of Ireland.
The braided-hair weed, Plocamium, from plokamos, braided hair, is the
pinky-red, ribless, much-branched, rather gristly weed, which, from
its elegant arborescence and beautiful color, is an especial favorite
with the workers in ornamental sea-weed decorations. It is cast up
in quantities on the British shores; but, as a rule, it lives beyond
the shore, that is to say, below low-tide level. Another equally
common weed has a slightly darker red color, and its frond is horny,
flat, branching in twos, and with little fronds on the edges. It is
found from the very verge of high water to the extreme of low water,
fringing the margins of the rock-pools, and is very common. From its
hard condition and horny nature it has been called Gelidium, from
_gelu_, frost. The beautiful red weed, whose resemblance to a great
branching tree pressed flat is so great, and which bears thousands
of little berry-looking knobs on short stalks, on the sides of its
fronds, is called Sphærococcus, or globe-fruit or berry. It is not
known on the eastern coast of Britain, but is common on the Irish
shores at extreme low-water mark. Another red weed, with a dull
purple color, has a frond of from six inches to two feet in length,
and every minute ramification of its skeleton-leaved frond has one or
more berry-shaped swellings. It is common all round the coast within
tide-marks, and has been called after a genus of mosses, Hypnæa.
The last kinds of filamentous, or skeleton-leaved red weeds, to be
noticed, are remarkable for their tufty nature, their spreading out
in water and showing tree-like branching from a stem, which, when
magnified, is seen to be made up of many long cells placed side by
side. Some live between tides on rocks, and others at the edge of low
tide, but the most interesting are parasitic upon other weeds. From
their many-tubed nature they are called Polysiphonia. The parasitic
kind (so named) is rather rare, and settles on some of the calcareous
weeds. The lanceolate kind is found on the stems and fronds of
the tangle; and a dark red species, called Formosa, is found near
low-water mark. Brodie’s Polysiphonia is known by the little tufts of
branches which come from the main branches, and it has a good stem.
It is found on corallines and on rocks.
The fibrous Polysiphonia has tufts at the end of its branches, and
is found on mussel-shells; and the violet kind is brownish-red or
purple, has a small root-like disk, and fronds which are from six to
ten inches in length. It is feathery and much branched.
It has been noticed that some sea-weeds are parasitic, or live
on others, fixed certainly, but whether they get any nourishment
through their roots is doubtful. One of these is very common on Fuci,
the bladder one especially; and it occurs as dense little tufts on
the leaves. These, when examined, are found to be made up of long,
flaccid, olive-colored hair-like filaments, about an inch in length.
They rise from a little hard spot, and form a tuft with a broad
circular outline. They belong to a genus called Elachista, from the
Greek word for “the least.” The hairy Ceramium is a tufty weed, which
is sometimes parasitic and sometimes not. It has a very peculiar
shape, being made up of filaments placed side by side in great
numbers, but they branch and rebranch, have little whorls of minute
prickles along them, and the ends curl gracefully.
Among the more remarkable sea-weeds is the Carrageen, or Irish moss.
It is a very variable plant in its color and shape, and it may be a
yellowish-green, a livid purple, or of a brownish tint, and it may
be in the shape of a wrinkled, crumpled fern, or of a bush. It has
a root-stem, reaches a foot in height, and the largest are found in
estuaries where mud comes down with fresh water. The weed is found
abundantly on the shores of Great Britain, and formerly was used in
the place of isinglass for making blanc-mange, an edible which has
degenerated with the progress of imitative culinary art. It was a
fashionable remedy for consumption, and many of the peasantry of the
west coast of Ireland used to collect it.
A most extraordinary fan-shaped sea-weed has a root covered with
woolly filaments and fronds, from two to five inches in length, wide
at the base, and expanding in almost perfect half-circles. The frond
is curved, marked across, and has a disposition to form funnel-shaped
pieces. A fringe of orange-colored filaments is on the markings, and
at the edge, which is often strongly rolled inward. The outer surface
is covered with a kind of whitish powder. The general color is yellow
and olive, with a dash of red. This peacock-tail weed is found on
rocks in shallow pools, on parts of the south of England coast, and
is abundant at Torquay. It is remarkable for being an extension,
northward, of a common tropical sea-weed.
A very common plant is to be found, either growing in little tufts
on the rocks at low-tide mark, or as a waif cast up by the waves, in
bunches, near where the coast contains rocks or earths which have
carbonate of lime in them. It is also a dweller in deeper water on
the floor of the sea, and oftentimes it may be seen waving lightly
in a rock-pool; but it does not look like a plant. There are no
leafy fronds, and it does not resemble any other common sea-weed in
outside appearance. It has a stony look, and is hard to the touch; it
will stand a pinch, and although it may break into separate pieces
it can hardly be crushed by the finger and thumb. Usually, as seen
by most people, it is of a glistening white color, with some purple
about it, and is made up of a number of joints. The coralline, for
so it is called, has a sort of broad crust where it adheres to the
rock, which gives out a stem. This stem is slender, and is made up
of many pieces, placed one before the other, narrow where they join,
and rather swollen in the middle or at the end. Other pieces, usually
two, come off from the piece at the joint, and there may be hundreds
of them or only a few. The end of the plant is made up of tufts of
pieces, some of which have a little hole in the end, as if there were
a hollow place. Now, if the spots where the pieces join be looked
at carefully, there appears to be something like very thin threads
uniting one piece to another, and they are not covered, as all the
rest is, with the glistening white stuff, which feels gritty between
the teeth. These corallines, if placed in vinegar, begin to bubble as
if they were made up of chalk, and their outsides are composed of a
mineral called carbonate of lime. After a while the vinegar dissolves
all the hard white part, and leaves the threads, which are now seen
to run the whole length of the coralline. These threads are portions
of vegetable fibre, and constitute the inside stem as it were, which
is surrounded by a sort of bark of carbonate of lime.
[Illustration: Lichens and Small Fungi
1, Lecanora; 2, Opeographa; 3, Parmelia; 4, Cetraria Islandica; 5,
11, Cladonia; 6, Usnea Barbata; 7, Red Wart Fungus; 8, Pertusaria; 9
Bæomyses; 10, Erysiphe; 12, Cyanthus]
But this is only a popular manner of explaining, for if more care
is taken, it will be found that, although some fibres run through
more than one joint, others, when they are in the midst of a piece,
turn outward from the middle, and come near the surface where the
carbonate of lime is. There they end in delicate bags or cells in
rows, the last of which is quite at the surface; so that the outside
of the pieces is made up of a mass of these small microscopic
cells, and the rest of the long fibres. The older the plant, the
more carbonate of lime is there in this mass of cells; but in very
young plants, in the spring of the year, there is but little of the
mineral, and they may sometimes be got quite soft. They are then
short little stumps fixed on to the expanded root, which sticks on
to stones, and they are not white, but of a beautiful claret or
port-wine color, the joints, where the fibres are, being greenish
or without color. This immature plant can be examined with the
microscope, and then the secret of how the carbonate of lime is
put in is divulged. First, it appears that any part of the young
coralline which is growing, does not have any of the opaque mineral
in it, and that the fibres never have it in them, nor has a very
delicate skin which covers the whole, and which is very difficult
to get a sight of, for it is easily washed off. By putting a young
piece in weak acid, bubbles come out, and every now and then one
blows up this exquisitely thin pavement-looking film from off the
surface. It is then seen to be made up of flat cells, placed side by
side, and colorless. This is the important tissue by which the plant
lives, for it exists long after all within is hard. It is always
growing and being repaired; and in the tropics, where the water is
warm, the little cells of it are covered with very long hairs, and,
indeed, they may sometimes be traced in English specimens. Leaving
these outside cells and the membrane for a while, it is necessary to
consider those beneath, and which are more or less connected with the
long fibres of the joints. A row of these more deeply seated cells
is on the outside, just beneath the membrane, and other rows are
deeper and deeper still, until the ends of the fibres are seen
to end, as it were, in contact with the innermost. The outer row
of all these is of a pale green color, and gradually the port-wine
tint comes with depth from the edge. Each of the cells of these rows
is not quite covered with the hard mineral, and they communicate
their fluid contents to another; and it is found that it is between
the cells that the carbonate of lime is deposited, and which can be
dissolved out by vinegar. As soon as a set of cells has done growing,
the mineral is deposited, invests, and comes outside them, until
it invades the delicate membranes of their bag as well. How does
this plant live? and where does it get its lime from? It does not
absorb anything by its root, for it is placed on a stone, but all
nourishment enters by the thin outside layer.
In all sea-water there is some organic stuff or sea soup, the
result of the decomposition of tiny things, and there is some air
in the water which contains oxygen and nitrogen and carbonic acid.
Under the influence of life, the organic stuff is absorbed by the
cell-membrane, and is rendered useful to the rest of the plant, into
whose cells, not quite walled up by carbonate of lime, it enters like
sap, and circulates. The carbonate of lime can only get in by there
being some minute quantity in the sea-water, and there is sufficient
in the chalky spots and limestone shores, not only dissolved by the
sea-water, but held in suspension by it. The water is ever on the
move, passing over the coralline, and in a few weeks a few grains,
for they make a great show, are absorbed and deposited in it. Small
sea-snails browse on the corallines, and have to thank them for their
lime, which is necessary for their shell.
There are some other plants found at low-tide marks which are
calcareous, but instead of being jointed, like the corallines, they
form irregular and rounded little blocks, or simple papery-looking
expansions on some of the larger-leaved sea-weeds. They are usually
white and hard, and no one would consider them to be of a vegetable
nature were their microscopic anatomy not known. They have a great
resemblance in mineral structure to the coralline, and are called
Melobesia or Nullipores.
The sea-weeds are, as may have been gleaned from the last few pages,
divisible into red, olive, or dark and green kinds, and one of their
most interesting studies relates to the method of reproduction.
Many sea-weeds are annual and die in the winter, so they must be
reproduced by seed, or something like it; others are of two or more
years’ growth, and outlive the winter, but in the end they must
have some method of perpetuating their kind. Some are perennial, or
constantly growing. Certain kinds are only found in the spring and
summer, others are always to be met with, and some produce spores, or
the matter out of which future weed grows, in summer, and others in
the autumn and winter. The geographical range of some of the British
sea-weeds is immense, and not a few kinds are found at the Antipodes.
SARGASSUM
--CUTHBERT COLLINGWOOD
Among the many remarkable phenomena connected with the Gulf Stream
not the least remarkable is the existence of those floating meadows
of sea-weed commonly known as the Gulf-weed or Sargassum, whose
accumulations, within certain parallels of latitude and longitude,
have given to that area the name of the Sargasso Sea. These marine
prairies, as they have been called, have attracted the notice of all
navigators since the time of Columbus, who, in his first voyage,
received his earliest check upon falling in with them. The great
pioneer entered the Sargasso Sea in lat. 26° N., and long. 48°
W., and his timid shipmates at once took fright at the marvelous
appearance, feeling assured that their ships would be entangled in
the weed until they were starved to death, or that they were about
to strike on some unknown coast. In this part, he says, “the sea was
covered with such a quantity of sea-weed, like little branches of the
fir-trees which bear the pistachio nuts, that we believed the ships
would run aground for want of water.” They could not understand how
such vast quantities of vegetation could merely float on the surface,
and the appearance of a lobster among the weed confirmed their fears;
and deeming it necessary that they must be either in, or approaching
shoal water, they entreated the heroic discoverer to turn the ship’s
head. But happily he never wavered, and on the tropic, in long. 66°,
the first vessel which had ever entered the Sargasso Sea emerged
again into clear water.
The extent of the Sargasso Sea is in due proportion to the vast
natural agency to which it primarily owes its existence. It stretches
from 20° to about 65° West longitude, and from between the parallels
of 20° and 45° is of considerable width, narrowing from 12° in its
widest part to about 4° or 5° where least developed; while the
remaining 20° of westerly extent takes the form of a narrow belt
of various detached tracts, influenced as to situation by local
currents, and averaging 4° or 5° only in width. An idea may be
obtained of its area by the comparison of Maury, who states that it
is equal to the great valley of the Mississippi; or still better,
perhaps, from Humboldt’s estimate, that it was about six times as
large as the Germany of his day.
But, although the geographical boundaries given above are those
usually recognized by hydrographers for the Sargasso Sea, it must not
be supposed that they are invariable. It may, however, be correctly
stated, that it occupies the great sweep made by the Azores,
Canaries, and Cape de Verde Islands in the East; while the elongated
westerly belt extends as far as between the Bermudas and West Indian
islands.
The earlier navigators often found the Gulf-weed a serious impediment
to their progress. Lærius mentions that for fifteen continuous
days he passed through one unbroken meadow (Praderias de yerva, or
sea-weed prairies, as Oviedo characteristically calls them), so that
he could find no way through for oars. On certain occasions it has
been found that the speed of vessels through the Sargasso Sea has
been materially retarded; and it has been described as so thick that,
to the eye, at a little distance it appears to be substantial enough
to walk upon.
That this is not the condition met with under all circumstances
is proved by the fact that passing through this region in 1867,
the writer made a seven days’ voyage through its central portion,
during which the sea was at no time covered with the weed, so as to
form a continuous meadow. It made its appearance usually in large
patches, generally upon the surface, but sometimes apparently sunk
to some distance below it. It varied considerably in appearance--was
sometimes dark-colored, dense, and compact, and covered with berries;
at others, pale and attenuated, with few berries. The masses, on
some days were round and shapely, and usually scattered somewhat
indiscriminately over the surface of the sea. Occasionally only a
few small tufts appeared for many hours; and on one day the only
sign of its presence was a long narrow streak, extending across the
ocean as far as the eye could reach in the direction of the wind.
The fact, indeed, is that the Sargasso Sea, dependent as it is upon
a great physical phenomenon, changes its position according to the
seasons, storms, and winds: its mean position remaining the same
as it has been ascertained by observations during many years past.
The Gulf Stream is the great power which maintains these marine
pastures--a current whose impulse and origin, according to Humboldt,
are to be sought to the south of the Cape of Good Hope--after a
long circuit it pours itself from the Caribbean Sea and the Mexican
Gulf through the Straits of the Bahamas, and following a course from
south-southwest to north-northeast, continues to recede from the
shores of the United States until, further deflected to the eastward
by the banks of Newfoundland, it approaches the European coast.
At the point where the Gulf Stream is deflected from the banks of
Newfoundland toward the east, it sends off branches to the south near
the Azores. This is the situation of the Sargasso Sea.
Patches of the weed are always to be seen floating along the outer
edge of the Gulf Stream. Now, if bits of cork, or chaff, or any
floating substance, says Captain Maury, be put in a basin, and a
circular motion be given to the water, all the light substances will
be found crowding together near the centre of the pool, where there
is the least motion. Just such a basin is the Atlantic Ocean to the
Gulf Stream; and the Sargasso Sea is the centre of the whirl.
The Gulf-weed itself has so peculiar a history that it forms not the
least remarkable point of interest in the description of the Sargasso
Sea. It is one of the numerous species of the genus Sargassum,
which is among the most natural and readily distinguished genera of
the family of Fucaceæ. The great cryptogamist, Agardh, enumerates
sixty-two species of Sargassum, of which the one concerning which
we are speaking is the Sargassum bacciferum, called Fucus natans by
Linnæus, and Fucus sargasso by Gmelin. The Spanish word Sargazo, or
Sargaço, meaning sea-weed, supplies its common English name.
The integument is leathery and the general color brown, of varying
shades, sometimes light and sometimes dark. The most striking
peculiarity, on a cursory view, is the abundance of globular cells,
which have been taken by the unlearned for fruit, but which are in
reality merely receptacles of air, by means of which the plant not
only floats upon the surface of the ocean, but also is enabled to
support vast numbers of marine animals, which find shelter among its
tangled fronds. Columbus, the first discoverer of the Sargasso Sea,
described the meadows as yellow like dry hay-seed, bearing leaves of
common rue, with numerous berries, which turn black in drying like
juniper berries. These berries have received the name of rasins de
tropique.