_SEA WEEDS_
We now pass from the animal to the vegetable kingdom, our object being
to give a general outline of the nature and distribution of the
principal marine algæ or sea weeds that grow on our shores; and to
supply a brief account of those flowering plants that either exhibit a
partiality for the neighbourhood of the sea, or that grow exclusively on
the rocks and cliffs of the coast. The present chapter will be devoted
to the sea weeds themselves, but we consider it advisable to precede our
account of these beautiful and interesting plants by a brief outline of
the general classification of plant-life, in order that the reader may
be able to understand the true position of both these and the flowering
plants in the scale of vegetable life.
Plants are divided into two great groups, the _Cryptogams_ or Flowerless
Plants and the _Phanerogams_ or Flowering Plants. In the former the
reproductive organs are not true seeds containing an embryo of the
future plant, but mere cells or _spores_, which give rise directly to a
thread or mass of threads, to a cellular membrane, or to a cellular body
of more or less complexity of form from which the flowerless plant is
afterwards developed; while in the latter the reproductive organs are
flowers that give rise to true seeds, each of which contains the embryo
plant.
The _Cryptogams_ are subdivided into four groups--the _Thallophytes_,
the _Charales_, the _Muscineæ_, and the _Vascular Cryptogams_.
The first of these includes all the very low forms of vegetable life,
the simplest of which (_Protophyta_) are minute plants, each consisting
of a single microscopic cell that multiplies by a process of budding, no
sexual organs of any kind being produced. Some of these minute
unicellular organisms contain chlorophyll--the green colouring matter of
plants, by the action of which, under the influence of light, the plant
is enabled to decompose the carbonic acid gas of the atmosphere, using
the carbon for the purpose of building up its own substance, and setting
free the oxygen into the air again. Others contain no chlorophyll; and
these, having no power of feeding on carbonic acid gas, are more or less
dependent on organic matter for their supplies of carbon.
Only very slightly removed from these minute plants are the _Algæ_ of
fresh and salt water, varying in size from microscopic dimensions to
enormous plants, the lengths of which may reach many yards and the
weight several stone. They contain chlorophyll, and can therefore avail
themselves of inorganic food material; and although some multiply only
by repeated subdivision of their cells, others develop sexual organs by
the union of which fertilised spores are formed. The nature of these
Algæ will be more fully described presently; and we will go no further
now than to justify the location of such large and conspicuous plants
(as many are) so low in the scale of vegetable life by stating that they
are entirely cellular in structure, never producing true vessels such as
we see in higher plants; and that though some of them develop parts
which more or less resemble the leaves and roots of higher forms, the
former are far more simple in structure and function than true leaves
and the latter are never engaged in the absorption of food from the soil
to which they are fixed.
Another important group of the _Thallophytes_ is formed by the _Fungi_,
which include the familiar mushrooms, toadstools, and the sap-balls so
commonly seen on decaying trees; also the smaller forms known as moulds,
mildew, and smut. These, also, are entirely cellular in structure; and,
since they develop no chlorophyll, are compelled to live as parasites on
living beings or to derive their food from decaying organic matter. Thus
they are the creatures of corruption, their presence always denoting the
breaking down of living matter or of matter that has previously lived.
Now leaving the _Thallophytes_, and passing over the small group of
aquatic plants known as the _Charales_, we come to the _Muscineæ_, which
contains the Liverworts (_Hepaticæ_) and the Mosses (_Musci_).
The plants of both these groups require much moisture, and are found
principally in damp, shady situations. Like the preceding groups they
are cellular in structure, never producing true vascular bundles such as
the higher plants possess; and their life histories are rendered
interesting by the ‘alternation of generations’ which they exhibit. The
first generation is a sexual one produced from the spores, and consists
either of a mass of delicate threads from which a plant with a leafy
axis is developed by a process of budding, or of a little green frond
(the _thallus_). These bear the male and female elements, called
respectively the _antheridia_ and the _archegonia_; and when the central
cells of the latter are fertilised by the former, they give rise to a
case, with or without a stalk, containing a number of spores. When the
case is ripe, it opens horizontally by means of a lid, thus liberating
the spores.
Following these in the ascending scale are the _Vascular Cryptogams_, in
which some of the cells become modified into true vessels. Here, too,
the plants exhibit a distinct alternation of generations, the spore
first giving rise to a small, leafless body, the _prothallium_, which
bears the sexual organs; and then the female elements, after
fertilisation, produce the spore-bearing plant.
This group contains quite a variety of beautiful and interesting plants,
including the Ferns (_Filicales_), Horsetails (_Equisetales_),
Club-mosses (_Lycopodiales_), Water Ferns (_Rhizocarpeæ_), and
_Selaginellales_.
Ferns usually produce their little green prothallia above ground, and
the perfect plant generally has a creeping rhizome or underground stem.
Some, however, have strong, erect, woody stems, such as we see in the
tree ferns of tropical and sub-tropical countries. The horsetails and
the club-mosses are also produced from prothallia that are formed above
ground. The perfect plants of the former have branching underground
stems which give off numerous roots, and send up annually green,
jointed, aërial stems that bear whorls of fine leaves, each whorl
forming a toothed, ring-like sheath. The fertile shoots terminate in
cones, on the modified leaves of which the sporangia are produced. The
stems of the club-mosses are clothed with small overlapping leaves, in
the axes of which the sporangia are produced; and the spores, which are
formed in abundance, constitute the lycopodium powder with which
druggists often coat their pills.
Water ferns either float on the surface of water or creep along the
bottom, and produce their fruit either at the bases of the leaves or
between the fibres of submerged leaves. The Selaginellas are
characterised by a procumbent stem that branches in one plane only,
producing small, sessile leaves, with a single central vein. A number of
roots grow downward from the under side of the stem, and the fruit is
developed in the axils of the leaves that form the terminal cones of the
fertile branches.
The above are all the principal divisions of the flowerless plants, and
we have now to note the general characteristics of the _Phanerogams_.
The chief of these is, of course, the possession of flowers as
reproductive organs; and although it is not convenient to give a full
description of the flower at the present time, it will be necessary to
say a little concerning it in order that we may be able to grasp the
broad principles of classification.
A flower, in its most complex form, consists of parts arranged in four
whorls arranged concentrically. The first and second whorls, commencing
from the outside, usually consist of leaf-like bodies, united or
distinct, and are called respectively the _calyx_ and the _corolla_. The
third whorl consists of _stamens_, which are the male reproductive
organs of the plant, and each stamen consists essentially of a case--the
_anther_--in which are formed a number of little _pollen cells_. When
the anther is ripe it opens, thus liberating the pollen, so that it may
be dispersed by insects, by the wind, or by other mechanical means. The
remaining whorl constitutes the _pistil_, which is generally made up of
parts (_carpels_) arranged round a common centre, and each surmounted by
a _stigma_ adapted for the reception of the pollen cells. This portion
of the flower contains the _ovules_, enclosed in a case called the
_ovary_, and is, therefore, the female organ of the plant. When the
ovules have been fertilised by the pollen, they develop into seeds, each
one of which contains an embryo plant; and the ovary itself, ripening at
the same time, develops into the _fruit_.
Such is the general description of a flower in its most complex form,
but it must be remembered that one or more of the whorls named above may
often be absent. Thus, calyx or corolla, or both, may not exist; and the
male and female organs may be developed on separate flowers of the same
plant, or even, as is frequently the case, on different plants of the
same species. In the latter instance the flowers are spoken of as
unisexual, those bearing the stamens being the staminate or male
flowers, and those bearing the pistil the pistillate or female flowers.
The _Phanerogams_ are divided into two main groups, the _Gymnosperms_
and the _Angiosperms_. In the former the ovules are naked, no ovary or
seed-case being developed. The pollen, carried by the wind, falls
directly on the ovule, and then develops a tube which penetrates to the
nucleus of the ovule, thus fertilising it. In the Angiosperms the
ovules are always enclosed in an ovary, and the pollen grains, alighting
on the stigma, are held by a gummy secretion. The tubes they produce
then penetrate through the underlying tissues, and thus come into
contact with the ovules.
The _Gymnosperms_ include a group of small palm-like trees and shrubs
(the _Cycadeæ_), of which the so-called Sago Palm is a representative;
and the _Coniferæ_ or cone-bearing shrubs and trees, which may be spoken
of collectively as the Pines. In the latter the leaves are either stiff,
linear, and needle-like, or short and scale-like, or are divided into
narrow lobes; and the plants are noted for their resinous secretions.
The flowers are always unisexual, and are generally arranged in
cylindrical or short catkins, where they are protected by closely packed
scales; but the female flowers may be solitary. There is no calyx or
corolla, but the naked ovules and seeds are sometimes more or less
enclosed in the scales (_bracts_) or in a fleshy disc.
The _Angiosperms_ form the highest division of the flowering plants; and
are subdivided into two extensive groups--the _Monocotyledons_ and the
_Dicotyledons_. The chief distinguishing feature of these is that
implied in the above names, the embryo of the former containing but one
rudimentary leaf (_cotyledon_), while that of the latter contains two.
The Monocotyledons are also characterised by having the bundles of
vessels (_vascular bundles_) of the stems dispersed; the veins of the
leaves are also usually parallel, and the parts of the flower are
arranged in whorls of three or six. In the Dicotyledons the vascular
bundles of the stem are united into a ring which surrounds a central
pith; the veins of the leaves form a network, and the parts of the
flower are arranged in whorls of four or five.
We are now enabled to understand the relative positions of the principal
groups of plants in the scale of vegetable life, and to locate
approximately the forms with which we have to deal; and to aid the
reader in this portion of his work we present a brief summary of the
classification of plants in the form of a table for reference:--
THE CLASSIFICATION OF PLANTS
I. =CRYPTOGAMIA=--Flowerless plants.
(_a_) =THALLOPHYTES=--Leafless, cellular plants.
1. =Protophyta=--Unicellular plants.
2. =Algæ=--Sea weeds, &c.
3. =Fungi=--Mushrooms, &c.
(_b_) =CHARALES.=
(_c_) =MUSCINEÆ.=
1. =Hepaticæ=--Liverworts.
2. =Musci=--Mosses.
(_d_) =VASCULAR CRYPTOGAMS.=
1. =Filicales=--Ferns.
2. =Equisetales=--Horsetails.
3. =Lycopodiales=--Club-mosses.
4. =Rhizocarpeæ=--Water ferns.
5. =Selaginellales.=
II. =PHANEROGAMIA.=
(_a_) =GYMNOSPERMIA.=
1. =Cycadeæ=--Cycads.
2. =Coniferæ=--Cone-bearing trees.
(_b_) =ANGIOSPERMS.=
1. =Monocotyledons.=
2. =Dicotyledons.=
We have now to deal more particularly with those marine _Algæ_ that are
commonly known as Sea Weeds, and which add so much to the beauty of our
rocky coasts. These exhibit such a variety of graceful forms, and such
charming colours, that they are admired and treasured by thousands of
sea-side ramblers, who are attracted by them merely on account of their
pleasing general appearance; but the naturalist has all this and a great
deal more to interest and instruct him, for the sea weeds possess quite
a number of peculiar and characteristic features that render them well
worthy of a detailed study, especially when they are compared and
contrasted with the better-known flowering plants of our fields, woods,
and hedgerows.
It has already been observed that sea weeds differ from the majority of
flowering plants in that they have no true roots or leaves, though they
are often attached to rocks and other substances by a root-like disc,
and sometimes have leaf-like expansions that are supported by stem-like
rods. The root-like structures, however, serve simply for the attachment
of the plant, and are never concerned in the absorption of nourishment
like the true roots of higher plants; and the leaf-like expansions,
though they are sometimes symmetrical in form, never exhibit the spiral
arrangement that obtains in the leaves of higher plants, from which they
also differ in function.
The plant-body of a sea weed is called a _thallus_, and differs
considerably in the various species. Sometimes it has no expanded
portion whatever, but is more or less cylindrical in all parts, and may
be either branched or simple; and in some species it forms a simple
crust or a soft jelly-like covering on a rock.
All portions of a sea weed are made up of cells, and these are never
modified into vessels such as we see in the stems, leaves, and roots of
higher forms of vegetable life; and one who is commencing the study of
the algæ will find much interesting work in the examination of their
microscopic structure. Thin sections of various parts of the larger
weeds, cut with a sharp knife or a razor, and examined in a drop of
water under a cover-glass, will show the cellular structure perfectly;
while minute fragments of the small and slender species are sufficiently
thin and transparent to display the form and arrangement of their cells
without any previous preparation.
One of the principal charms of the marine algæ lies in the great variety
of colour that they display. They all contain chlorophyll--that
remarkable green colouring matter which enables a plant, under the
influence of light, to feed on the carbonic acid gas existing in the
atmosphere, or held in solution in water; and with its aid the sea weeds
can utilise this product of decay and animal respiration that would
otherwise accumulate in the water of the sea. But, in addition to this
bright green chlorophyll, many of the sea weeds contain a second
colouring substance, and in these the great variety of tint is dependent
on the nature of the latter and on the proportion in which it is present
as compared with the chlorophyll itself.
The different means by which the algæ reproduce their kind forms a most
engrossing subject, and to the botanist a most important one, for it has
much to do with the classification of the species. The affinities of
plants may be better determined by the nature of their reproductive
processes than by any other features, but unfortunately this is not so
well understood with regard to the algæ generally as compared with many
other divisions of the vegetable kingdom; and, as a consequence, there
is still a considerable difference of opinion, not only as to the extent
of the whole group, but also as to its divisions and subdivisions. The
reason for this is clear; for while it is quite an easy matter to trace
a flowering plant through its complete cycle from seed to seed, it
requires a much more careful examination, combined with much microscopic
work, to trace a lowly organised plant from spore to spore.
Some of the algæ may be reproduced without the agency of any sexual
elements; that is, without the aid of parts that correspond with the
ovules and the fertilising pollen of a flowering plant. Some of these
are reproduced by a repeated subdivision, or by the separation of a
portion of the plant that is capable of independent growth; while others
produce spores that do not result from the fusion of two different
cells. In most, however, sexual differences are to be observed, some
cells being modified into female organs, containing one or two more
minute bodies that are capable of developing into new plants after they
have been fertilised, and other cells produce the male elements by means
of which the fertilisation is accomplished. The fertilised cells are
spores, but are named differently according to the nature of their
development. They all differ from true seeds in that they never contain
an embryo plant, but germinate by the elongation of some particular
part, which subsequently grows by a continuous process of cell-division;
or the cell-division may originate directly in the spore without any
previous elongation or expansion.
The sea weeds are usually classified according to the colour of their
spores; but, since this colour generally corresponds with that of the
plant itself, we may almost say that they are grouped according to their
general tints. There are three main divisions:--
The _Chlorospermeæ_, or Green-spored;
The _Rhodospermeæ_, or Red-spored; and
The _Melanospermeæ_, or Brown-spored.
The _Chlorospermeæ_ contain no colouring matter other than the
chlorophyll. They are mostly small weeds, of a delicate green colour;
and, although they are not particularly conspicuous on our shores, they
contribute very considerably to the beauty of the rock pools, where
their delicate green fronds contrast richly with the olive
_Melanosperms_ and the pink and white corallines. The thallus or
plant-body is very varied in form, sometimes consisting of a broad
membrane, but more commonly of tufts of slender green filaments or of
narrow, flattened fronds.
These weeds are most beautiful objects for the microscope, and they are
generally so thin and transparent that no section-cutting is necessary,
nothing being required except to mount very small portions in a drop of
water. In this simple manner we may study the beautiful arrangement and
the various forms of the cells of which they are composed. The more
delicate species will be found to consist of a single layer of cells
only, while in the larger forms--the _Ulvaceæ_, for example--the thallus
may be formed of two or three distinct layers, and some of the cells may
be elongated into tubes.
A remarkable feature of the green-spored weeds is the large size of the
chlorophyll granules as compared with those of the other groups, and
also the great variety of forms which these granules assume. They may be
easily seen under a low power, and the examination of the weeds will
show that the thalli are not uniformly green, but that the colour of the
plants is due entirely to the chlorophyll granules, the remainder of the
plant substance being quite colourless.
If a green sea weed be placed in alcohol for a short time, it will be
found that the liquid assumes a green colour, while the plant itself
becomes colourless. The explanation is, of course, that chlorophyll is
soluble in alcohol. The presence of starch also in the weed may be
proved in a very simple manner, as follows:--Mount a small piece in
water, and then put a drop of iodine solution by the edge of the
cover-glass. The solution will gradually diffuse itself around the
object, turning the starch-grains to a deep blue colour, and so
rendering them very conspicuous under a moderately high power.
The manner in which the green weeds are reproduced is very interesting
also. In some cases the fragments of a thallus that have been detached
by storms or other mechanical means possess the power of independent
growth, and develop into plants; and this mode of reproduction may often
be watched in the indoor aquarium. Another method is by the agency of
little spores (_zoospores_) that are produced at the edges or
extremities of the thallus. Certain of the cells become modified into
what are called _zoosporangia_, and the minute zoospores are formed
within them. The walls of the cells either gradually degenerate, or are
fractured, and the zoospores are thus set free. The latter are provided
with little vibratile cilia, by which they move about freely in the
water. Some eventually settle down and germinate without any further
aid, but others are unable to develop until they have been fertilised by
fusion with another cell. The former is therefore an _asexual_
development, while the latter is _sexual_.
Some of the delicate, filamentous green algæ are reproduced by another
process termed _conjugation_. In this case two adjacent threads that lie
close together become lightly united by a covering of gelatinous
substance, and a cell of each throws out a process. The processes are
directed towards each other, and unite to form a tube in which the
contents of the two cells become fused together, with the result that
zoospores are produced.
Among the lowest of the green sea weeds are the plants known
collectively as the _Confervaceæ_, which consist of delicate green
filaments, usually attached to rocks in dense masses, but often found
floating freely in the rock pools. The filaments are composed of cells
joined together at their ends, and are always unbranched.
Confervæ are found principally in the tide pools, especially near
high-water mark, and often abound in hollows in the rock even above
high-water mark, where the spray of the waves is mingled with rain-water
or the drainage from the land. They exist in both fresh and salt water,
and some species seem capable of thriving in brackish water of any
degree of salinity.
Allied to the confervæ is a group of marine algæ called _Cladophora_,
very similar to the former in general appearance, and found in similar
situations, but readily distinguished by the branching of their jointed
filaments. The various species of this group are very beautiful weeds,
their delicate filaments looking very pretty as they float and sway in
the water of the pools. They are also exquisite objects for the
microscope; but, unfortunately, often lose their natural colour when
preserved dry. They vary in colour, some few being of a dull green tint,
while others are bright green, sometimes with a beautiful silky gloss.
One species (_C. pellucida_) is more rigid than most of the others; its
fronds stand out erect and firm, and are repeatedly forked near the
tips. It is a moderately common weed, found in the lower rock pools, and
may be readily recognised by the long one-celled joints, from the tops
of which the branches proceed. Another species (_C. diffusa_) is also
very firm in structure, so much so that its bristly tufts retain their
form when removed from the water, instead of becoming matted together in
a shapeless mass. Its branches are rather long, and bear a few simple
branchlets towards their extremities. It is found in rock pools between
the tide-marks. _C. lanosa_ is a very pretty little weed, growing in
dense globular woolly tufts, an inch or more in diameter, on the olive
tangles between the tide-marks. It is of a pale yellowish-green colour,
which becomes much paler, or is even altogether lost, when the plant is
preserved in a dry state, and, at the same time its fine glossy
appearance is lost. Its fronds have straight branches, all making very
acute angles, and they have also small root-like filaments. It much
resembles another species (_C. arcta_), which grows in dense tufts on
rocks, but the latter is larger, not so slender, and more freely
branched. The cells, too, of _C. arcta_ are longer, being about ten
times the length of the diameter, and the fronds are silvery at the
tips.
Nearly thirty species of _Cladophora_ have been described, but it is
impossible to give here a detailed description of all. We add, however,
a brief summary of the distinguishing features of a few other species
that are common on our coasts.
_C. rupestris_ is common everywhere, and easily recognised by its rigid,
branching, tufted fronds, of a dark greyish-green colour; its branches,
which are opposite, bear awl-shaped branchlets. It is found in rock
pools from half-tide downwards, and in deep water beyond the tide-marks,
the plants growing in the latter situations being generally of a fine
dark-green colour.
_C. lætevirens_ is also very common on rocks between the tide-marks. Its
fronds are tufted and freely branched, of a pale-green colour and soft
flexible texture, and about six inches long. The branchlets are usually
slightly curved.
_C. gracilis_ is a beautiful plant that grows on large weeds, especially
the Sea Grass (_Zostera_) in deep water; and although not very common,
it is sometimes found on the beach after storms. It is characterised by
its slender silky fronds, from a few inches to a foot in length, of a
yellowish-green colour. It may always be known by the comb-like
branchlets growing only on one side of each branch.
_C. refracta_ grows in dense tufts, two or three inches long, in rock
pools near low-water mark. Its fronds consist of rigid stems in
rope-like bundles that are very freely branched, the whole tuft being of
a yellow-green colour and silky texture. _C. albida_ closely resembles
it in structure and habit, but may be distinguished by its paler colour,
which disappears when the weed is dried, and by its longer and more
delicate branches.
In another order of the green-spored algæ (the _Siphoneæ_ or
_Siphonaceæ_) the frond is formed of single branching cells, and many of
these are often interwoven into a spongy mass, and sometimes coated with
a deposit of calcareous matter.
In the genus _Codium_ the fronds are of a sponge-like texture, composed
of interwoven branching fibres, and are of a globular, cylindrical, or
flattened form. The commonest species is _C. tomentosum_ (Plate VII.),
which consists of sponge-like, dark-green cylindrical fronds, which are
forked and covered with short hairs that give it a woolly appearance
when in the water. Each frond is composed of slender interwoven fibres
with club-shaped filaments passing vertically to the surface. It grows
on rocks in the pools between the tide-marks, and is abundant on nearly
all our coasts.
The Purse Codium (_C. bursa_) has spongy hollow fronds of a globular
form, varying from a quarter of an inch to five or six inches in
diameter. It is a rare species, being found only at a few places on the
south coast. Another species (_C. adhærens_) adheres to rocks, over
which the fronds spread in irregular soft patches, the club-shaped
vertical filaments of its interwoven fibres giving it the appearance of
rich green velvet.
An allied weed (_Bryopsis_), named from its moss-like appearance, grows
in erect tufts, each frond consisting of a branched one-celled filament.
There are two species of the genus, one (_B. plumosa_) characterised by
the light feathery nature of its fronds, the stems of which are branched
only near the top. It is found in rock pools on most of our coasts. The
other (_B. hypnoides_) is more freely branched, and the branches are
long, and issue from all sides of the stem. Like the last species, it
has branches on the outer part of the stem only, but it is of a softer
texture.
The best known of the green-spored weeds are certainly those belonging
to the _Ulvaceæ_, characterised by their flat or tubular fronds,
sometimes of a purplish colour, the cells of which multiply both
horizontally and vertically as the plants grow. In the typical genus,
_Ulva_, the frond is sometimes in two distinct layers, and becomes more
or less inflated by the accumulation of either water or oxygen between
them. The commonest species are _U. lactuca_ and _U. latissima_, both of
which are eaten by the dwellers on some of our coasts. The former,
commonly known as the Lettuce Ulva, has a frond of a single layer of
cells, and grows on rocks and weeds between the tide-marks. It is common
on many oyster beds, and is employed by the fishermen to cover the
oysters when sent to market; they call it ‘oyster green.’ This species
is shown on Plate VIII. _U. latissima_ or the Broad Ulva sometimes
reaches a length of two feet, and a breadth of nearly a foot. The fronds
are composed of two layers of cells, are of an irregular shape, with a
very wavy, broken margin, and of a bluish-green colour, It is known
as the Green Laver, and is used as food in districts where the true
laver (_Porphyra_) is not to be obtained. A third species--the Narrow
Ulva (_U. Linza_)--has smaller and narrower fronds, of a more regular
shape and of a bright-green colour. The fronds are composed of two
layers of cells.
[Illustration: Plate VII.
SEA-WEEDS
1. Fucus nodosus
2. Nitophyllum laceratum
3. Codium tomentosum
4. Padina pavonia
5. Porphyra laciniata]
The _Ulvæ_ retain their colour perfectly when dried, and, with the
exception of _U. latissima_, are of a mucilaginous nature, and adhere
well to paper, but, unfortunately, the graceful wavy outline of the
fronds is lost in pressed specimens.
The ‘true laver’ mentioned above, which is also popularly known as
Sloke, is closely allied to _Ulva_, but may be distinguished from it by
the colour of its membranous fronds, which vary from a light rose to a
deep purple or violet, occasionally inclining to olive, but never green.
Its scientific name is _Porphyra laciniata_ (Plate VII.), and it differs
from the majority of the _chlorospermeæ_ in having dark-purple spores,
which are arranged in groups of four in all parts of the frond. The
fronds are very variable in form and size, being sometimes ribbon-like,
and sometimes spreading into an irregular sheet of deeply-divided
segments; and the remarkable variety of form and colour has led to a
division into several species. These, however, merge into one another so
gradually that the separation seems to be hardly necessary.
The same remark concerning the multiplicity of species applies to
another allied genus called _Enteromorpha_, in which the fronds are
green and tubular, and often more or less branched. In these the colour
varies from a pale to a dark green, and the cells are arranged in such a
manner as to give a reticulated appearance. The commonest and
best-defined species are _E. intestinalis_, the tubular fronds of which
are constricted at intervals in such a manner as to resemble the
intestines of an animal, and _E. compressa_, with branched fronds of
variable form and size. The former is common on all our coasts, and may
even be found in rivers and ditches some distance from the sea. It
thrives equally well in fresh and salt water, and appears to grow most
luxuriantly in the brackish waters of tidal rivers. The latter species
also thrives best in similar situations.
Coming now to the red-spored sea weeds (_Rhodospermeæ_), we have to deal
with some of the most charming of the marine algæ that invariably
attract the sea-side rambler, and provide many of the most delightful
objects in the album of the young collector. Their brilliant colours,
varying from a light red to dark purple and violet, are sufficient in
themselves to render them popular with the collector, but in addition to
this striking feature they are characterised by extreme elegance of form
and delicacy of texture. They are to be found in most rock pools, from
near high-water mark downwards, the smaller and more delicate forms
adding much to the beauty of these miniature seas; but the largest and
many of the prettiest species exist only at or beyond the lowest ebb of
the tide, and hence the algologist, in quest of these beautiful plants,
will find it necessary to work at the very lowest spring tides, with the
occasional aid of a small boat drifted into the narrow channels among
outlying rocks, and a long hook with which to haul up submerged
specimens; and it will also be advisable to search the line of débris at
high-water mark after stormy weather for rare weeds that may have been
detached and washed ashore by the angry waves.
While engaged in the former of these employments--the searching of
outlying rocks with the boat--and also when examining the outer rock
pools which are disturbed by the waves that wash over their banks, the
simple instrument known as the water-telescope will prove invaluable.
Everyone must have noticed how difficult it is to observe objects in
water, the surface of which is disturbed by the wind or some other
cause; but the simple appliance named, consisting only of a long tube of
metal, a few inches in diameter, and painted a dead black inside, will
enable the observer to see all submerged objects with the greatest of
ease when the water is itself clear. The principle of the
water-telescope is as simple as its construction; for the tube,
protecting the surface of the water within it from the disturbances
outside, prevents the light from being refracted successively in
different directions, while the dead-black surface of the interior
prevents those internal reflections that would otherwise cause the
vision to be indistinct.
A few hours spent with the rhodosperms at the sea-side will be
sufficient to show not only the great variety of their form and
colouring, but also that the same species may vary according to the
position in which it grows. Most of the smaller forms are delicate and
filamentous, but others have expanded fronds which are very leaf-like.
The brightest colours are usually to be found at or beyond low-water
mark, where the weeds are covered with a considerable height of water
for hours together, and also in shady situations at higher levels, while
some of the species that grow in the upper rock pools are often of such
a deep colour, with so much admixture of brown, that they may be easily
mistaken for the olive melanospores to be presently described.
Most of the rhodosperms are attached directly to the rocks, and the
larger species have often a root-like disc by which they are very firmly
held; but some of the smaller species grow attached to larger weeds,
into the substance of which they frequently penetrate; and it is
possible that these derive some amount of nourishment from the sap of
their supporters. Some are of a recumbent nature, being attached to the
rock throughout their whole length, while others are so incrusted with
carbonate of lime which has been extracted from the water that they
resemble corals rather than forms of vegetable life. Nearly all of them
contain a bright-red colouring matter in addition to the chlorophyll by
which they are enabled to feed on carbonic acid gas.
None of the rhodosperms are of really microscopic dimensions, and they
all grow by the repeated division of the cells of the apex, while the
branches are derived by the similar division of new cells at the sides.
All plants are particularly interesting during the period of fruiting,
and this is remarkably the case with many of our red-spored sea weeds,
which are brighter and prettier while laden with their spore-producing
cells; and the collector of marine algæ should always endeavour to
obtain as many species as possible in fruit, not only on account of the
brighter appearance that may characterise them at this time, but mainly
because the opportunity of studying the mode of reproduction should not
be missed.
In the rhodosperms the reproduction may be either asexual or sexual. In
the former case fertile spores are produced without the necessity for
any outside fertilising element, and four are usually produced in each
one of the sporangia, hence they are generally known as _tetraspores_.
Where the reproduction is of the sexual type, the male cells are
produced singly in the terminal cells of the fronds, and since they are
usually crowded together in considerable numbers, and contain none of
the red colouring matter that exists in the other parts of the plant,
their presence is easily observed.
The female cells (_carpogonia_) are also produced on the tips of the
branches, and when the male elements escape from their cells, they are
conveyed passively by the movements of the water, for they have no
vibratile cilia by which they are propelled, and on coming into contact
with the female cell they adhere closely. An opening is then formed in
the latter, and the male element enters the carpogonium, which
germinates, deriving its nourishment from the parent plant, and the
spores are thus formed. Lastly, it is interesting to note that the
asexual spores, the male cells, and the female cells are generally
produced on different plants of the same species.
We will now proceed to examine some of the best known and most
interesting of the rhodosperms, beginning with the order _Ceramiaceæ_,
which contains a number of red or reddish-brown weeds with jointed,
thread-like fronds that enclose a single tube, and which are generally
surrounded by a cuticle of polygonal cells. The spores are contained in
transparent berry-like sacs which are naked; and the four-parted spores
(_tetraspores_) are formed in the cells of the cuticle or at the tips of
the fronds.
Over twenty British species belong to the genus _Callithamnion_, and
nearly all of them are pretty red or rose-coloured, feathery plants that
are conspicuous for their beauty. Nearly all are of small size, the
largest measuring only seven or eight inches, while some are so small
that they would scarcely be noticed except by those who search
diligently for them. The principal features of the genus are, in
addition to those mentioned above as common to the order, that the
spores are angular, and clustered within a transparent sac, and the
tetraspores are naked and distributed on the branches.
In some species the fronds have no stem, and these are very small,
generally only about a quarter of an inch in height or less, and they
grow on rocks or weeds, sometimes clothing the surfaces with a
velvet-like covering. _C. floridulum_ forms a kind of reddish down on
the rocks, sometimes in little rounded patches, but sometimes completely
covering the surface. It occurs on several parts of the English coast,
but is so abundant on the west coast of Ireland that the beach is strewn
with it after stormy weather. Other allied species grow in minute tufts
on rocks, or are parasitic on other weeds, and are so inconspicuous that
they are but little known.
Another section of the genus is characterised by pinnate fronds with
opposite segments, and the species are very pretty plants with fronds
generally a few inches in length. One of the commonest of these is the
Feathered Callithamnion (_C. plumula_), a great favourite with
collectors of sea weeds, and a most interesting object for the
microscope. Its soft and flexible fronds grow in tufts from two to five
inches long. The branches are regularly arranged, and the comb-like
branchlets bear the tetraspores on the tips of the plumules. This
beautiful weed grows near low-water mark, and in deep water, and is
often very abundant on the beach after storms. _C. Turneri_ is another
common species, easily known by its creeping fibres, attached by little
discs to some larger weed, and from which the tufts of branched fronds
stand out erect. On the west and south-west coasts of Britain we may
often meet with the allied Crossed Callithamnion (_C. cruciatum_), which
grows on rocks, close to low-water mark, that are covered with a muddy
deposit. It grows in tufts, somewhat resembling those of _C. plumula_,
but its plumules are arranged two, three, or four at a level, and are
very crowded at the tips of the branches.
[Illustration: FIG. 245.--_Callithamnion roseum_]
[Illustration: FIG. 246.--_Callithamnion tetricum_]
Still another section of this large genus contains weeds of a more
shrubby growth, with veined stem and branches jointed obscurely. Of
these the Rosy Callithamnion (_C. roseum_) is not uncommonly found on
muddy shores, and especially in and near the estuaries of rivers. It
grows in dense dark-coloured tufts, two or three inches long, with
alternate branches much divided. The tetraspores occur singly, one at
the top of each of the lower joints of the pinnules of the plumes. _C.
byssoideum_ grows on larger weeds in the rock pools, and especially on
_Codium tomentosum_ (p. 353), in dense tufts of exceedingly fine
filaments, jointed, and branched irregularly. The upper branches are
plumed, and their tips bear very fine colourless filaments. The
spore-clusters are arranged in pairs, and the tetraspores are thinly
scattered on the pinnules of the plumes. This species is so very
delicate in structure that a lens is absolutely necessary to make out
its structure. It is, in fact, impossible to distinguish between the
various species of Callithamnion without such aid; and many of them,
particularly the species last described, require the low power of a
compound microscope.
Among the other common species, belonging to the same section, we may
mention _C. corymbosum_, distinguished by its very slender, rosy,
jointed fronds, with the ultimate divisions of the branches disposed in
a level-topped (_corymbose_) manner, growing on rocks and weeds near
low-water mark; _C. polyspermum_, growing in globular tufts on _Fucus
serratus_ and _F. vesiculosus_, with short awl-shaped pinnules, and
closely-packed clusters of spores; _C. Hookeri_, with opaque stem and
branches, and spreading branchlets that are themselves branched, and
bear spreading plumules at their tips; and _C. arbuscula_, found on the
west coasts, with a stout stem, naked below, and having a very bushy
habit.
It is often by no means an easy matter to distinguish between the
different species in such a large genus as _Callithamnion_, and we
strongly recommend the beginner to first study the characteristics on
which the classification of the _Algæ_ is based, and to arrange his
specimens according to the orders and genera to which they belong; and
then, after mastering the principles of classification, he should refer
to one of those larger works in which all known British species are
described, and make himself acquainted with the features of each
individual species in his collection.
Before leaving the present genus we ought also to mention the fact that
many of the species lose their natural colour rapidly when placed in
fresh water; hence when they are being cleansed for mounting salt water
should be employed. Further, even after they have been satisfactorily
mounted, they are liable to be spoiled if left exposed to moist air. The
salt water used need not be the natural sea water; a solution of common
table salt, made up to approximately the same strength as sea water,
will answer the purpose just as well.
The genus _Griffithsia_ includes some very beautiful weeds of delicate
threadlike structure and of a fine rose colour. The frond contains a
single tube, and is jointed and forked, the joints being usually
transparent. The spore clusters are enclosed in a gelatinous sac
surrounded by a whorl of little branchlets, the spores themselves being
minute and angular. The tetraspores are attached to the inner side of
whorled branchlets.
The commonest species is _G. setacea_, which is of a bright-red colour
and slightly branched. It is also of a somewhat firm structure, but soon
loses both firmness and colour when removed from salt water; and, like
_Callithamnion_, rapidly fades if put into fresh water, which is
readily absorbed through its membranes, causing them to burst and
discharge their colouring matter. It receives its specific name from its
bristle-like forked fronds. _G. secundiflora_ is somewhat like
_Setacea_, but is larger, and the tips of its branches are obtuse. Its
fronds grow in fan-shaped tufts five or six inches long. It is not a
common weed, but may often be met with on the coast of Devon and
Cornwall.
[Illustration: FIG. 247.--_Griffithsia corallina_]
_G. barbata_, or the Bearded Griffithsia, receives its name from its
very delicate fibres, which bear spherical, pink tetraspores. It seems
to occur only on the south and south-west coasts, where it grows on
stones or attached to other weeds. Our last example of the genus is _G.
corallina_, which is of a deep-crimson colour, and is so jointed as to
have the appearance of a coralline. Its fronds are from three to eight
inches long, regularly forked, and of a gelatinous nature. The joints
are somewhat pear-shaped, and the spore clusters are attached to their
upper ends. It soon fades, and even if its colour is satisfactorily
preserved, the pressure of the drying press destroys the beautiful
rounded form of its bead-like joints. It forms a lovely permanent
specimen, however, when preserved in a bottle of salt water, with the
addition of a single grain of corrosive sublimate.
[Illustration: FIG. 248.--_Halurus equisetifolius_]
[Illustration: FIG. 249.--_Pilota plumosa_]
Our next genus (_Halurus_) contains a common weed of the south coast
which was once included in _Griffithsia_. It is the Equisetum-leaved
Halurus (_H. equisetifolius_), so called because its branches are
regularly whorled round the nodes of the jointed branches, thus
resembling the semi-aquatic Mare’s Tail. Its frond is tubular, and the
spore-clusters are situated on the tips of the branches, surrounded by a
whorl of small branchlets.
The genus _Pilota_ has a slightly flattened cartilaginous frond, divided
pinnately, and the axis surrounded by a cuticle of two layers of cells.
The spore-clusters, at the tips of the branches, are surrounded by a
whorl of branchlets. It contains only two British species, one of which
(_P. plumosa_) is a very feathery species, with comb-like branchlets,
growing on the stems and fronds of other weeds found on our northern
shores. The other (_P. elegans_), with narrower fronds, in long flaccid
tufts, is found all round our coasts.
Our last genus of the _Ceramiaceæ_ is the large and typical one
_Ceramium_, which contains about a dozen British species in which the
frond is threadlike, jointed, branched or forked repeatedly, with the
tips of the branchlets usually curled. The spore-clusters are enclosed
in transparent sessile sacs, surrounded by a whorl of very short
branchlets; and the tetraspores are embedded in the cortex, but
distinctly visible. As a rule the fronds are very symmetrical, and the
branches radiate in a regular fan-like manner.
In one species of the genus the frond is completely covered with cortex
cells, and at each node of the frond there is a single spine which,
although so small as to be invisible without a lens, so effectually
locks the threads together that they form an entangled mass that is not
easily arranged to the satisfaction of the collector. The species
referred to is _C. flabelligerum_--the Fan-bearing Ceramium--and is very
rare except in the Channel Islands.
Other species are armed with one or more spines at the nodes, but the
nodes only are covered with cortex cells, which render them opaque,
while the internodes or joints are transparent. In this group we have
_C. ciliatum_--the Hairy Ceramium, with reddish-purple segments, and a
regular whorl of hairs, directed upwards, round each node; each hair or
spine consists of three segments. This plant is common during the summer
and autumn, and may be found in the tide pools at all levels, either
attached to the rocks or parasitic on other weeds. The same section
contains _C. echinotum_, with rigid, forked fronds, and
irregularly-scattered one-jointed spines; it is common on the south
coast, where it may be found on the rocks and weeds of the upper tide
pools; and _C. acanthonotum_, also common in the rock pools, with a
single strong three-jointed spine on the outer side of each filament.
The last-named weed is found principally on the northern shores,
especially on rocks covered with the fry of the common mussel.
Other species are characterised by transparent internodes as above
described, but have no spines at the joints, and may thus be easily
floated on to a sheet of paper without the troublesome matting of their
fronds. These include the Straight Ceramium (_C. strictum_), with erect
and straight branches growing in dense tufts, and conspicuous
tetraspores arranged round the nodes of the upper branchlets, _C.
gracillimum_, of the lower rock pools, with very slender gelatinous
fronds, swollen nodes and small fan-shaped branchlets; _C. tenuissimum_,
closely resembling _C. strictum_ in general appearance, but
distinguished by having its tetraspores only on the outer side of the
nodes; and the Transparent Ceramium (_C. diaphanum_), which may be found
throughout the year on rocks and weeds in the rock pools. The last
species is the largest and most beautiful of the genus, and may be
readily recognised by its light-coloured, transparent stem with swollen
purple nodes, and its conspicuous spore-clusters near the tips of the
filaments.
[Illustration: FIG. 250.--_Ceramium diaphanum_]
Our last example of the genus is the Common Red Ceramium (_C. rubrum_),
which may be found in the rock pools at all levels. It is very variable
in form, but may be known by its contracted nodes, in which the red
tetraspores are lodged, and its spore-clusters surrounded by three or
four short branchlets. It differs from most of the other species in
having both nodes and internodes covered with cortex-cells, and hence
the latter are not transparent.
The order _Spyridiaceæ_ has a single British representative which may be
found in various localities on the south coast. It is _Spyridia
filamentosa_, a dull-red weed with thread-like, tubular, jointed fronds,
from four inches to a foot in length. The main stem is forked, and
densely clothed with short and slender branchlets. The frond is covered
with a cortex of small cells. The spore-clusters are grouped together,
several being enclosed in a membranous cell in conceptacles, or external
sacs, at the ends of the branchlets; and the tetraspores are arranged
singly along the jointed branchlets.
The next family (_Cryptonemiaceæ_) is an extensive one, containing
nearly twenty British genera of red or purple weeds, with unjointed,
cartilaginous, gelatinous, and sometimes membranous fronds. The spores
are irregularly distributed, and are contained either in sunken cells or
in conceptacles. The tetraspores are either in cells at the edges of the
frond or collected together in compact groups.
Of the genus _Dumontia_ we have only one species (_D. filiformis_), the
frond of which is a simple or branched tube, from an inch to more than a
foot in length, containing a loose network of filaments when young, and
only a gelatinous fluid when the plant is mature. The spores exist in
rounded clusters among the cells of the tube, and the tetraspores are
similarly situated. A variety with wide wavy fronds is sometimes found
in the brackish water near the mouths of rivers.
_Gloiosiphonia capillaris_ is a very delicate and beautiful weed found
in the lowest tide pools of the south coast. Its frond is a very slender
branched tube, filled with a gelatinous fluid, and composed of delicate
filaments embedded in transparent gelatine. It is a beautiful object for
the microscope.
_Schizymenia_ (_Iridæa_) _edulis_ has flat, oval, dark-red fronds that
grow in clusters; and, being eaten by various marine animals, is often
found imperfect and full of holes. The fronds are sometimes a foot or
more in length, and five or six inches wide. They are thick and
leathery, and each is supported on a short, cylindrical stem.
In the lower tide pools we commonly meet with _Furcellaria fastigiata_,
with brownish-red, cylindrical fronds, solid, forked, and densely
tufted. The branches are all of the same height, with sharp tips; and
the spore-clusters are contained in terminal lanceolate pods. This weed
is very much like _Polyides_, of another order, but may be distinguished
by its fibrous, creeping root, while that of _Polyides_ is a disc.
The genus _Chylocladia_ is characterised by a tubular rounded frond
composed of two layers, the inner consisting of branching filaments, and
the outer cellular. The spores are contained in external cones with a
pore at the apex, and the tetraspores are among the superficial cells of
the branches. There are two common British species of the genus, one of
them--_C. articulata_--with long, tubular fronds, constricted at
intervals, the lower branches forked and the upper whorled and tufted;
and _C. clavellosa_, with freely branched fronds bearing short
spindle-shaped branchlets.
One of the best-known algæ of the present family is the Irish Moss or
Carrageen (_Chondrus crispus_), which will be at once recognised by its
representation on Plate VIII. Its fronds are cartilaginous, forked and
fan-shaped; and, when growing in deep, sheltered pools, its branches are
often broad and much curled. This weed is an important article of
commerce, being still used as a food for invalids. When boiled it
yields a colourless gelatine.
In the genus _Gigartina_ the frond is cartilaginous, flat, or
threadlike, irregularly branched, and of a purplish-red colour. The
spores are contained in external tubercles, and the tetraspores are
arranged in masses beneath the surface. The only common species is _G.
mamillosa_, which has a linear, furrowed stem, with fan-shaped,
deeply-cleft fronds. The spores are contained in mamilliform tubercles
scattered over the surface of the frond.
_Callophyllis_ (_Rhodymenia_) _laciniata_ is found on most rocky coasts.
It has bright-red, fleshy fronds that are deeply cleft into wedge-shaped
segments, the fertile specimens with waved edges and small marginal
leaflets. It is found on rocks and Laminaria stems beyond the
tide-marks, but is commonly washed up on the beach during storms. It is
a beautiful weed, and retains its colour well when dried.
_Cystoclonium_ (_Hypnæa_) _purpurascens_ is a very common weed, growing
on other algæ between the tide-marks, and sometimes reaching a length of
two feet. Its cartilaginous, purple fronds are much branched, and become
almost black when dried. The spores are embedded in the smallest
branches, and the tetraspores are arranged among the superficial cells.
The genus _Phyllophora_ contains a few British weeds with a stiff,
membranous frond, bearing leaf-like appendages, and supported on a
stalk. The tetraspores are contained in external wart-like swellings.
The commonest species is _P. membranifolia_, the fronds of which are
divided into wedge-shaped segments, and grow in tufts from an expanding
root. The spores are contained in stalked sporangia, and the tetraspores
are near the centres of the segments. Another species--_P. rubens_--has
a shorter stem, and grows in deep and shady rock pools. Its fronds are
densely tufted; and, as the plant grows, new series of segments are
formed at the tips of the older ones. A third species (_P.
palmettoides_) has a very bright-red frond and an expanded root.
The order _Rhodymeniaceæ_ includes a number of red or purple sea weeds
with flat or thread-like unjointed, cellular fronds, the surface cells
forming a continuous coating. The spores are lodged in external
conceptacles, and are at first arranged in beaded threads. The
tetraspores are either distributed among the surface cells, collected in
clusters, or situated in special leaflets.
The typical genus (_Rhodymenia_) contains two red, membranous weeds,
the commoner of which is _R. palmata_ (Plate VIII.), so common on the
Scottish and Irish coasts, where it forms an important article of diet,
and is known as the Dulse or Dillisk. It is also widely distributed over
the English coasts. Its broad, fleshy fronds are divided into
finger-like lobes, and are either sessile or supported on a stalk that
proceeds from a small discoid root. The frond is very variable in form,
being sometimes divided into very narrow segments, and sometimes quite
undivided. One variety has a number of small stalked leaflets on its
margin (see Plate VIII.); and another is very narrow, with wedge-shaped
irregular lobes. _R. palmetta_ is a smaller and less common species that
grows on rocks and large weeds in deep water. The tetraspores form
crimson patches on the tips of the lobes.
_Maugeria_ (_Delesseria_) _sanguinea_ (Plate VIII.) is a large and
beautiful weed, of a blood-red colour, that grows in the lower rock
pools or beyond low-water mark, under the shade of high rocks or hidden
by the olive tangles. Its frond is thin and membranous, with a
well-defined midrib. The spores are contained in globular stalked
conceptacles, usually on one side of the midrib; and the tetraspores may
be seen in pod-like leaflets attached to the bare midrib during the
winter.
Passing over some of the rarer membranaceous _Rhodymeniaceæ_, we come to
the beautiful _Plocamium_, distinguished by its linear compressed
crimson fronds, which are pinnate, with comb-like teeth, the branchlets
being alternately arranged on either side in threes and fours. The
spores are on radiating threads, in globular conceptacles; and the
tetraspores are in the outer divisions of the frond. We have only one
species of this beautiful genus, and that is _P. coccineum_, which is of
such a brilliant colour that it is always a favourite with collectors.
[Illustration: FIG 251..--_Plocamium_]
Our last example of the order is _Cordylecladia_ (_Gracilaria_)
_erecta_, with threadlike, cartilaginous frond, irregularly branched and
cellular in structure. The fronds arise from a disc-like root; and bear
spores in thickly-clustered spherical conceptacles, and tetraspores in
lanceolate pods at the tips of the branches, both in the winter. It is a
small weed, and grows principally on sand-covered rocks near low-water
mark.
The order _Sphærococcoideæ_ contains red or purple sea weeds with
unjointed cartilaginous or membranaceous fronds, composed of many-sided,
elongated cells, with spores in necklace-like strings, lodged in
external conceptacles. The typical genus (_Sphærococcus_) contains the
Buck’s-horn sea weed which grows at and beyond low-water mark on the
south and west coasts, where it is sometimes washed up on the beach
during storms. Its fronds are flattened and two-edged, freely branched,
and the upper branches are repeatedly forked, and terminate in
fan-shaped, cleft branchlets. Both branches and branchlets are fringed
with slender cilia, in which the spores are embedded. It is a handsome
weed, of a bright-red colour and a somewhat coral-like form.
Allied to this is _Gelidium corneum_, with flattened, horny fronds,
repeatedly pinnate, with the smallest branchlets obtuse and narrower at
the base. The spores are contained in conceptacles near the extremities
of the branchlets, and the tetraspores are imbedded in club-shaped
branchlets. There are a large number of varieties of this species,
differing in form, size, and the mode of branching of the fronds. The
size varies from one to five or six inches, and the colour is red or
reddish green.
In the genus _Gracilaria_ the frond is thick and horny, and the surface
cells are very small, while the central ones are large. The spores,
formed on necklace-like threads, are enclosed in sessile conceptacles
along the branches, and the tetraspores are imbedded among the surface
cells of the fronds. The only common species is _G. confervoides_, with
cylindrical cartilaginous fronds bearing long thread-like branches,
sometimes reaching a length of two feet. The spore conceptacles are
situated on the slender branches, giving them a knotted or beaded
appearance. The colour is a dark purple, which rapidly fades when the
weed is placed in fresh water or left exposed to the air. Two other
species--_G. multipartita_ and _G. compressa_--are rare.
_Calliblepharis ciliata_, perhaps more commonly known as _Rhodymenia
ciliata_, has a branching root, short round stem, and a broad, crisp
frond that is generally ciliated. Sometimes the frond is simple and
lanceolate, with small leaf-like appendages on its edge; and sometimes
it is deeply cleft. The spores are arranged in beaded threads in sessile
conceptacles on the marginal leaflets. Another species of the same genus
(_C. jubata_) is very similar in structure, but is of a duller-red
colour, gradually changing to olive green at the tips; and it has its
tetraspores in the cilia only, while in _C. ciliata_ they are collected
in patches in all parts of the frond. Both species grow in deep water,
and are frequently washed up during storms.
The large genus _Nitophyllum_ contains some beautiful rose-red sea
weeds, with irregularly cleft membranaceous fronds, either veinless, or
with a few indistinctly visible veins only at the base. The spores are
in rounded sessile conceptacles scattered on the surface of the frond;
and the tetraspores occur in clusters similarly scattered.
One of the species--_N. laceratum_--so called from the torn and jagged
appearance of the frond, is represented on Plate VII. The fronds are
attached to a disc-like root, and are very variable in form, being
sometimes so narrow as to appear almost threadlike. The plant grows on
rocks and large weeds in the lower rock pools and in deep water. In the
same genus we have _N. punctatum_, with broad pink fronds, dotted all
over with spore-conceptacles and dark-red clusters of tetraspores; also
a few other less common species that are seldom seen except after
storms, as they grow almost exclusively in deep water.
The genus _Delesseria_ contains some beautiful rose-coloured and
reddish-brown weeds with delicate, leaf-like, symmetrical fronds, each
of which has a darker midrib from which issue transverse veins. The
spores are arranged like minute necklaces, and are contained in sessile
conceptacles either on the midrib of the frond or on leaflets that grow
from the midrib. The tetraspores are in clusters which are scattered
over the frond or on its leaflets. The algæ of this genus are seldom
found growing between the tide-marks, as they generally thrive in deep
water, but splendid specimens are often washed up on the beach during
storms, especially on the south and south-west coasts.
[Illustration: FIG. 252.--_Delesseria alata_]
[Illustration: FIG. 253.--_Delesseria hypoglossum_]
Among these we may specially mention _D. alata_, known popularly as the
Winged Delesseria, with a dark-red, forked frond, consisting of a
strong midrib, bordered by a wing-like lamina of very variable width,
supported by opposite veins. In this species the clusters of tetraspores
are arranged on each side of the midrib or special leaflets near the
tips of the frond. _D. sinuosa_ is a less common weed, with a disc-like
root and an oblong, cleft and toothed frond, and tetraspores in leaflets
growing from its margin. Another species--_D. hypoglossum_--is
characterised by the leaflets of the midrib bearing still smaller
leaflets in the same manner.
We have already referred (p. 366) to a sea weed commonly known as the
Dock-leaved Delesseria, the scientific name of which is _Maugeria_
(_Delesseria_) _sanguinea_. This plant was once included in the present
order, but has been removed on account of the different structure of its
fruit.
Our next order is the interesting one containing the coral-like weeds,
some of which are so common and so conspicuous in the rock pools. The
order is known as the _Corallinaceæ_, and all its species secrete
carbonate of lime, which hides their vegetable structure and gives them
more the appearance of stony corals.
The typical genus (_Corallina_) includes two weeds with jointed pinnate
fronds, and spore-conceptacles at the tips of the branches with a
terminal pore.
These and the allied sea weeds are very unlike plants in their general
nature, their stony covering of carbonate of lime hiding all traces of
the delicate cellular structure so characteristic of the various forms
of vegetable life, and especially those of aquatic or marine habit. If,
however, the weed is put into dilute hydrochloric (muriatic) acid the
calcareous matter will be completely dissolved in a minute or two, with
evolution of bubbles of carbonic acid gas; and if a portion of the frond
be then examined in a drop of water under the microscope, the cellular
structure referred to will be seen as well as in any other weed. Another
characteristic of the plant, or rather of the carbonate of lime which it
secretes, is its property of becoming intensely luminous when held in a
very hot flame. Thus if a tuft of coralline be held in the flame of a
Bunsen burner, it will glow so brilliantly as to remind us of the lime
light. Further, if we examine the plant in its natural state, we find
that the carbonate of lime is not secreted uniformly in all parts, but
that the nodes of the jointed frond are free from the stony deposit, and
are therefore flexible.
Our commonest species--_C. officinalis_--may be found in almost every
rock pool between the tide-marks, growing on rocks, shells, and other
weeds. The joints of the stem and branches are cylindrical or somewhat
wedge-shaped, while those of the branchlets are linear; and the colour
varies from a dark purple to white, the former prevailing in the deep
and shady pools and the depth of tint decreasing according to the amount
of exposure to the bleaching action of the sun.
A second species (_C. squamata_) is very similar in growth and habit,
but is much less common, and is confined to the neighbourhood of
low-water mark. It may be distinguished from the last by the form of the
segments, which are short and globose in the lower portions of the stem,
and become broader and more flattened towards the tips of the branches.
Another genus--_Jania_--contains a few coralline weeds that are somewhat
like _Corallina_, but are of a more slender habit and smaller, and have
a moss-like appearance. They may be distinguished by the _forked_
branching of the slender frond, and by the position of the conceptacles
in the axils of the branches, and not at the tips. _J. rubens_ is a very
common red species that grows in tufts on other weeds. It has
cylindrical segments, longer towards the tips of the branches; while
another and less common one (_J. corniculata_), found principally on the
south coasts, has flattened segments except in the branchlets.
A third genus of the order--_Melobesia_--contains a very peculiar group
of algæ that would certainly never be regarded as plants by those who
did not know them. They are apparently mere solid incrustations of
calcareous matter, without any jointed structure, and often of very
irregular form, covering the surfaces of rocks, shells, or weeds. They
are of varying colours, some prevailing tints being dark purple, lilac,
rose, and yellow; and they are equally variable in form, some being
decidedly lichen-like, some resembling fungoid masses, and others
consisting of superimposed leaf-like layers. They are not weeds to be
pressed for the collector's album, but require storing in boxes or trays
like sea shells. As in the case of the branched corallines, the hidden
vegetable structure may be revealed by dissolving away the carbonate of
lime; and the spore-conceptacles, with terminal pores, may be seen
scattered irregularly over the surface.
The order _Laurenciaceæ_ contains some beautiful pink, red, and purple
weeds with round or flattened branching fronds. They may be known by the
disposition of the tetraspores, which are irregularly scattered over the
branches; and by the pear-shaped spores in rounded capsules. The
typical genus (_Laurencia_) includes an abundant weed (_L. pinnatifida_)
which was formerly eaten in parts of Scotland, where it is known as the
Pepper Dulse on account of its peppery taste. It is found in the tide
pools on many parts of the coast, and varies much in size, form, and
colour according to the situation in which it grows. The plants which
are exposed to the air at low tide are usually small, and of a pale
brown colour, while those found in the permanent rock pools at or near
low-water mark are larger and dark brown or purple. The fronds are flat
and cartilaginous, with stout branches bearing alternate divided
branchlets, which are blunt at the tips. The stem itself is unbranched.
The spores are pear-shaped, in oval cells; and the tetraspores are
irregularly distributed near the tips of the branches.
Another common species, known as the Tufted Laurencia (_L. cæspitosa_),
is very similar to the last mentioned, and is not easily distinguished
from it. It is, however, of a bushy habit, while _L. pinnatifida_ is
flat, and its fronds are less firm. This species grows on rocks and
stones between the tide-marks, and is variegated in colour from a pale
green to a purple.
[Illustration: FIG. 254.--_Laurencia pinnatifida_]
[Illustration: FIG. 255.--_Laurencia obtusa_]
A third species--the Obtuse Laurencia (_L. obtusa_)--is widely
distributed on our coasts, and may be known by its thread-like bipinnate
fronds with short blunt branchlets, cup-shaped at the tips. It is
parasitic on various other weeds.
The genus _Lomentaria_ includes a few weeds with tubular fronds that are
constricted at intervals, and divided internally by transverse
membranous septa. The spores are pear-shaped and lodged in spherical
cells; and the tetraspores are scattered on the surface of the branches.
One species called the salt-wort (_L. kaliformis_) is widely
distributed. Its colour is pink, sometimes yellowish, and it grows on
rocks or stones, and sometimes on other weeds. It may always be known by
its spherical fruit, without any visible opening, containing crimson
pear-shaped spores. Another species (_L. ovalis_), found on the coasts
of Devon and Cornwall, may be recognised by its _solid_ branched frond
and little oval leaf-like branchlets, which are hollow, jointed, and
divided by partitions internally.
The one remaining order of the red-spored sea weeds is the
_Rhodomelaceæ_, which has either a jointed or a many-tubed axis, and the
surface divided up into little definite areas. The fronds are either
leafy or thread-like, and the prevailing colours are red, reddish brown,
and purple. The spores are pear-shaped, and occupy the terminal cells of
tufted threads in external, globular, or rounded conceptacles; and the
tetraspores are lodged in special receptacles, or in special modified
branchlets. The order contains some of our most beautiful weeds, while
some of its members are of a very dark colour and unattractive form.
The typical genus--_Rhodomela_--contains two British species with
dark-red, cartilaginous fronds, cylindrical, unjointed, and irregularly
branched; and the tetraspores imbedded in the tips of the slender
branchlets. The name of the genus signifies ‘red-black,’ and is applied
on account of the tendency of the dark-red fronds to turn black when
dried.
_R. subfusca_ is very common on all our coasts. It has rigid fronds,
irregularly branched; and is in its best condition during the summer.
The other species--_R. lycopodioides_--has long undivided branches with
thickly-set and freely-divided branchlets.
When turning over the fronds of different species of the larger olive
weeds we commonly find them more or less clothed with tufts of
filamentous plants, sometimes small and delicate, and sometimes larger
and of more robust growth, varying in colour from a purplish brown to a
dark violet, and the articulated filaments more or less distinctly
striated with parallel lines. These weeds belong to the genus
_Polysiphonia_, and derive their generic name from the fact that the
threadlike fronds are composed of several parallel tubes. The surface
cells are also arranged in regular _transverse_ rows, and it is this
which gives rise to the striated appearance above referred to.
Over twenty species of _Polysiphonia_ are to be found on our shores,
where they exist at all levels between the tide-marks. They are
distinguished from one another partly by their general form and mode of
growth, and also by the number of tubes in their threadlike fronds.
Although they would not always be considered as lovely weeds and are
often anything but beautiful when dried and mounted, yet in their fresh
condition they are generally pretty objects, and their microscopic
structure is particularly interesting on account of the beautiful and
symmetrical arrangement of their siphons and tubes.
If the reader is the fortunate possessor of a compound microscope, it
will amply repay him to make transverse sections of the fronds for
examination. A short length of the frond should be inserted into a slit
cut in a piece of carrot or elder pith; and, while thus supported, very
thin transverse sections may be easily cut with a sharp razor, care
being taken to keep both razor and object very wet during the process.
Allow the sections to fall into a vessel of water as they are cut, and
then select the thinnest for examination, mounting them in a drop of
water in the usual way.
Specimens in fruit should always be obtained when possible, so that the
nature of the fructification may be observed. Two kinds of spores may be
seen in each species, but, as is usually the case with the red sea
weeds, on different plants. Some are small pear-shaped bodies, enclosed
in oval cells at the tips of the fronds; and the others are arranged in
clusters of four in swollen parts of the threads.
The commonest species is _P. fastigiata_, which may be found in
abundance as bushy brownish tufts on the fronds of _Fucus nodosus_ (p.
386). A transverse section of this weed is a very beautiful microscopic
object. It resembles a wheel, with a dark centre to the nave, and
several spokes enclosing about sixteen regularly arranged tubes. The
swollen tips of fronds should also be examined for the urn-shaped cells
containing the spores; and if a gentle pressure be applied to the
cover-glass with a needle, the little pear-shaped spores may be
expelled. The other kind of spores may be found near the bases of the
branches on different plants.
[Illustration: FIG. 256.--_Polysiphonia fastigiata_]
Among other species we may briefly mention--_P. parasitica_, sometimes
found near low-water mark, growing in little feathery tufts of a
bright-red colour, on the lichen-like _Melobesia_ or on corallines. It
has seven or eight parallel siphons in its fronds, all regularly
arranged round a small central space.
_P. Brodiæi_ is moderately common on our coasts. This is a large brown
species, with seven siphons surrounded by a thick cellular layer which
conceals the articulations and is too opaque to allow the siphons to be
seen without dissection. Its branches, which are alternate, bear short
tufts of delicate branchlets.
[Illustration: FIG. 257.--_Polysiphonia parasitica_]
[Illustration: FIG. 258.--_Polysiphonia Brodiæi_]
_P. byssoides_, so called on account of the pink filaments that fringe
the fronds, has also seven siphons. It is a large and beautiful weed,
moderately common on our coasts, of a bright-red colour, with
conspicuous fructification. The branches are alternate, and the
branchlets are clothed with the byssoid filaments above referred to.
_P. violacea_ is of a reddish-brown colour, with long silky alternate
branches, and four siphons. It receives its specific name from the fact
that it turns to a violet colour when dried.
_P. nigrescens_ has, as the specific name implies, blackish fronds, and
these are freely branched. The tubes, about twenty in number, are flat,
and are arranged round a large central space.
[Illustration: FIG. 259.--_Polysiphonia nigrescens_]
Our last example--_P. atro-rubescens_--is of a dark reddish-brown
colour, with rigid and densely-tufted fronds. It has twelve tubes,
arranged _spirally_ round a central cavity. It is common in the lower
rock pools of some coasts.
In the same order we have the genus _Chondria_, so called on account of
the cartilaginous nature of its thread-like fronds. These are pinnately
branched, and the club-shaped branchlets taper below. The main stem is
jointed and contains many siphons. The genus includes a common species
(_C. dasyphylla_), with thick fronds, that is found in shallow sandy
pools, where it grows on pebbles, shells, or on other weeds, the colour
varying from pink to a dark purple. _C. tenuissima_ is a very similar
weed, but may be distinguished by its more slender growth, and by its
long, rod-like simple branches, clothed with slender, bristle-like
branchlets that taper from the middle towards both ends.
On the northern coasts of Britain we may meet with _Odonthalia dentata_,
the blood-red fronds of which are tufted, and arise from a hard,
disc-like root. Each frond projects from the axil of a tooth-like
projection of the main stem, and is deeply pinnatifid, with a distinct
midrib in the lower part, and thin and membranaceous towards the tip.
The pinna are dentate, and the spores are in stalked, oval conceptacles
in the axils of the pinnæ. The tetraspores are similarly situated in
stalked, lanceolate leaflets.
The weeds of the genus _Rytiphlæa_ are very similar to some of the
_Polysiphonia_, the axis of the frond being jointed and transversely
striped, but the nodes are less distinct and are not constricted. They
are shrub-like weeds, with tufted spores in oval, sessile conceptacles;
and tetraspores in spindle-shaped branchlets or in little pod-like
leaflets. The principal British species are:--
_R. pinastroides_, a much-branched and shrub-like weed, of a dull-red
colour, which turns black when the plant is dried. The branches have
rigid, hooked branchlets arranged in such a manner as to give a combed
appearance. This species occurs on the south coast, and is in its prime
in very early spring. It is often rendered peculiarly interesting by the
colonies of zoophytes and the patches of _Melobesia_ with which it is
more or less covered.
_R. fruticulosa_ is another shrubby species, with irregularly branched,
interlacing stems. It is to be found in the rock pools of the south and
west coasts, and is of a deep-purple colour in the deeper shady pools,
but varying to a yellowish tint where exposed to the full light of the
sun. The whole of the frond is covered with hooked branchlets, and the
weed is peculiar for the fact that, when removed from the rock pool,
little glistening beads of water remain attached to the tips of the
terminal branches. The tetraspores are situated in distorted branchlets.
_R. thuyoides_ has creeping, fibrous roots, from which arise the erect
stems of purple-brown, branched fronds with short spine-like branchlets.
It occurs in the shallower rock pools, where it grows attached to rocks
or to other weeds. It is in its best condition during the summer, when
we may see its oval spore-conceptacles and the tetraspores in distorted
branchlets.
The last genus of the _Rhodomelaceæ_ is _Dasya_, which contains some
very graceful and brightly-coloured weeds that are found principally on
our south and west coasts. In these the fronds are thread-like or
flattened, branched, and without visible joints. The main stem contains
many tubes, but the tubular structure is hidden by the outer layer of
cells; and the branchlets, which are slender, one-tubed, and jointed,
bear little lanceolate pods that contain the tetraspores.
_D. ocellata_ has small tufted fronds, about two or three inches long,
attached to a small discoid root. The main stems are densely covered
with slender, forked branchlets, those at the tips being clustered in
such a manner as to recall the eye-like marks of the peacock’s tail. It
grows principally on the mud-covered rocks beyond low-water mark, and is
not by any means a common weed. Another species--_D. arbuscula_--is
somewhat plentiful on parts of the Scottish and Irish coasts, but
comparatively rare in South Britain. It has a small disc-like root, and
stems thickly clothed with short branchlets. The spore-conceptacles are
tapering, on short stalks, and the tetraspores are contained in pointed
pods on the branchlets. The scarlet Dasya (_D. coccinea_) may be
commonly seen at and beyond low-water mark during late summer, at which
time splendid specimens may also be found on the beach after storms. Its
stem is thick, proceeding from a discoid root, and is clothed with
hair-like filaments; and the branches bear short, slender branchlets
that give them a feathery appearance. The tetraspores are contained in
elongated, pointed, and stalked pods. There are three other species on
the British list, but they are not common weeds.
The last of the three great groups into which the sea weeds are divided
is the _Melanospermeæ_, or olive-spored algæ, the different species of
which are generally very readily distinguished by their olive-green or
olive-brown colour, for the whole plant, as well as the spores, contains
a dark olive colouring matter, in addition to the chlorophyll which is
always present.
These weeds are often very large, frequently attaining a length of
twenty feet or more in our seas, and from eighty to a hundred feet in
warmer parts; and, being also extremely abundant almost everywhere, they
form a most conspicuous feature of the shore. They usually grow on rocks
and stones, from high-water mark to moderately deep water, but some of
the smaller species are pseudo-parasitic on other algæ.
Their form is most varied. Some are minute filamentous plants,
consisting only of slender jointed threads, and others are mere
shapeless masses; but many of the larger species exhibit a great
differentiation of form, having root-like and stem-like structures, and
expansions that resemble leaves. The latter, too, often have large
vesicles that contain air, sometimes arranged singly along the median
line of the frond, or in lateral pairs, or a single vesicle at the base
of each segment of the thallus.
The air vesicles, of course, serve to buoy up the plant when it is
submerged, thus enabling the light to penetrate between its fronds to
lower portions; and when the plants have been wrenched from their
moorings by the force of the waves, they immediately rise to the surface
and are drifted on to the shore or accumulate in the eddies of the
surface currents. In this way immense masses of floating weeds are
formed, the most remarkable being that of the Sargasso Sea in the North
Atlantic.
Like other algæ, the melanospores grow by a continued process of
cell-division, and when portions of the thallus are worn away during
stormy weather, they are renewed by the same process.
The cell-walls of many species are very mucilaginous, the gelatinous
covering being either the result of the degeneration of the cell-walls
themselves, or the secretion of special glands.
As with the last division, the reproduction of the melanospores may be
asexual or sexual. The asexual spores, which are not motile, are formed
in some of the surface cells of the thallus. The male and female sexual
organs, called respectively the _antheridia_ and the _oogonia_, are
produced in cavities on special portions of the thallus, both kinds
being often formed in the same cavity or depression. The latter contains
from one to eight little bodies called _oospheres_. These escape and
float passively away when the wall of the oogonia ruptures. The
antheridia are also discharged whole, but the minute fertilising
elements (_antherozoids_), which are eventually set free from them,
swarm round the oospheres, being attracted by the latter. Soon one of
the antherozoids enters the oosphere, and from that moment all
attraction ceases, the remainder of the antherozoids floating passively
away; and the oosphere, previously naked and barren, now develops a
cell-wall, and becomes the fertile progenitor of a new plant.
Starting with the lowest of the melanospores, we first deal with the
order _Ectocarpaceæ_, which is characterised by olive, thread-like,
jointed fronds, with spores on the branchlets or embedded in their
substance; two kinds of spores often existing in the same plant.
The typical genus (_Ectocarpus_) contains many British species, though
several of them are rare. They are soft and flexible weeds, generally of
a dull olive colour, with slimy, tubular fronds, and grow in tufts on
other weeds or on mud-covered rocks. Spores of various shapes are
scattered over the fronds, and are also contained in pod-like bodies
formed of the branchlets. This latter feature is, perhaps, the best
distinguishing characteristic of the genus, but it is not an easy matter
to identify the several species it contains.
_E. tomentosus_ is very commonly found on _Fucus_ and other weeds, where
it forms matted tufts of slender threads of a yellowish-brown colour.
The threads are clothed with transparent cilia, and together form a
dense, spongy mass. The spores are contained in narrow pods supported on
short stalks. _E. littoralis_ is another common species, of a very
unattractive appearance. It grows in matted tufts on other weeds, on
rocks, mud, or any submerged object, and its spores are contained in
linear swellings of the branches. This species thrives well in brackish
water, and may be seen far up certain tidal rivers.
[Illustration: FIG. 260.--_Ectocarpus granulosus_]
[Illustration: FIG. 261.--_Ectocarpus siliculosus_]
[Illustration: FIG. 262.--_Ectocarpus Mertensii_]
Among the other species we may briefly mention _E. granulosus_, an
abundant and beautiful weed that grows in feathery tufts on rocks and
weeds, with elliptical, stalkless pods, quite visible to the naked eye,
freely distributed over the opposite branchlets; _E. siliculosus_, a
pale olive, parasitic species with lanceolate stalked pods, pointed and
striped; _E. sphærophorus_, a small, soft, brownish-yellow species, with
dense matted branches and spherical pods arranged either opposite to one
another or to a branchlet; and _E. Mertensii_, a pretty species that
grows on muddy rocks, freely branched but not matted, and having pods
enclosed by the branchlets. The last species is rare, but may be found
in Cawsand Bay and a few other localities about Plymouth Sound. The
genus includes several other species, but all these are more or less
rare.
In the genus _Myriotrichia_ we have two parasitic species with fragile,
hair-like, jointed fronds bearing simple straight branches that are
covered with transparent fibres. In these the spore-cases are rounded
and transparent, and arranged along the main threads; and the dark olive
spores are readily visible within. In _M. filiformis_ the branchlets are
short, and clustered at intervals, thus giving a somewhat knotted
appearance to the threads, and both branches and branchlets are covered
with long fibres. The other species--_M. clavæformis_--is very similar,
but may be distinguished by the arrangement of the branchlets, which are
not clustered at intervals, but are distributed regularly, and are
longer towards the tip of the frond, giving the appearance of minute
fox-brushes.
[Illustration: FIG. 263.--_Sphacelaria cirrhosa_]
[Illustration: FIG. 264.--_Sphacelaria plumosa_]
The genus _Sphacelaria_ contains several British weeds with rigid
branched and jointed fronds, most easily distinguished by the tips of
the branches, which are flattened, contain a granular mass, and have a
withered appearance. _S. cirrhosa_ forms hair-like tufts of slender
fibres with closely-set branches on small weeds, the tufts varying from
a quarter of an inch to over an inch in length. The fronds are naked at
the base, and the spore-cases, which are globular, are arranged on the
branches. _S. filicina_ is, as its name implies, of a fern-like
appearance, but is very variable in form. Its fronds vary from one to
three inches in length, and the spores are arranged singly in the axils
of the branchlets. Excluding some rarer species we mention one other
example--the broom-like _S. scoparia_, the frond of which is coarse and
very rigid, of a dark-brown colour, two or three inches long, with the
lower portion clothed by woolly fibres. Its spores are arranged in
clusters in the axils of the branchlets.
[Illustration: FIG. 265.--_Sphacelaria radicans_]
The last genus of the _Ectocarpaceæ_ is _Cladostephus_, which grows in
dark-green tufts, usually five or six inches long, in the deeper tide
pools. The fronds are cylindrical, branched, inarticulate, and rigid;
and the branchlets, which are short and jointed, are arranged in whorls.
The spores are situated in short accessory branchlets, or in masses at
the tips of the ordinary branchlets. _C. verticillatus_ is a very common
species, the whorled branchlets of which are deciduous in winter, when
the accessory branchlets that bear spores begin to develop. _C.
spongiosus_ is densely clothed with branchlets, and is of a bushy habit,
with a very spongy feeling. It is by some regarded as a variety of _C.
verticillatus_.
[Illustration: FIG. 266.--_Cladostephus spongiosus_]
[Illustration: FIG. 267.--_Chordaria flagelliformis_]
The order _Chordariaceæ_ is characterised by a compound gelatinous or
cartilaginous frond, consisting of interlacing horizontal and vertical
threads. The spores are not external as in the _Ectocarpaceæ_, but
contained in cells in the substance of the frond. In the typical genus
the frond has a cylindrical, branched, cartilaginous axis, surrounded by
whorls of club-shaped threads and slender gelatinous fibres. We have
only one common species--_Chordaria flagelliformis,_ the fronds of which
are from four to twenty inches long, of uniform thickness throughout,
with long, glistening, soft and slimy branches among which the spores
are disposed. It may be found in rock pools at almost all levels.
In the genus _Elachista_ there are some very small and peculiar weeds
that are almost sure to be overlooked by inexperienced collectors. They
are parasitic, and are composed of two kinds of jointed threads, the
inner of which are forked and combined into a tubercle, while the outer
are simple and radiate from the tubercle. The spores are attached to the
inner threads. The largest species (_E. fucicola_) is parasitic on
_Fucus_, growing in brush-like tufts about an inch long. Some of the
smaller ones are mere star-like tufts of no attractive appearance, and
would be disregarded as troublesome parasites by most young collectors,
but all of them are very interesting objects for the microscope.
The members of the genus _Myrionema_ are similarly liable to be
neglected, for they are minute parasites appearing only as decaying
spots on larger weeds, but nevertheless form interesting studies for the
microscope. Like the last group, they have two sets of jointed fibres,
the inner being branched, and spread over the surface of the plant on
which it grows, while the outer are simple and stand out at right
angles, but all are united into a rounded mass by a gelatinous
substance. Perhaps the best known is _M. strangulans_, which infests
_Ulva_ and _Enteromorpha_, producing the appearance of small decaying
spots.
In the genus _Leathesia_ we have other unattractive weeds, the jointed
and forked threads of which are all united together into tuber-like
fronds that are common on rocks and weeds between the tide-marks. There
are three or four species, all similar in general appearance, with the
spores distributed among the outer threads. These weeds cannot be
satisfactorily pressed and dried in the usual way, and should be
preserved in formaldehyde or dilute spirit, when they will always be
available for microscopic examination.
The last genus of the _Chordariaceæ_ is _Mesogloia_, so called because
the central axis of loosely-packed, interlacing threads is covered with
gelatinous substance. Around this axis there are radiating, forked
threads which are tipped with clubbed and beaded fibres among which the
spores are distributed. One species (_M. vermicularis_), common in most
rock pools, is of a wormlike form, of a dirty olive or yellow colour,
with soft, elastic fronds growing in tufts from one to two feet long.
_M. virescens_, also a common species, is of a pale greenish or olive
colour, and very soft and slimy. Its stem is round and slender, freely
branched, with short, simple branchlets.
The order _Dictyotaceæ_ contains the olive weeds with inarticulate
fronds, and superficial spores disposed in definite lines or spots. In
the typical genus (_Dictyota_) the frond is flat and forked, somewhat
ulva-like and ribless, and the spores are produced in little superficial
discs just beneath the cuticle. There is only one British species--_D.
dichotoma_--but that is a very common one, and it assumes a great
variety of forms as regards the shape and division of its fronds
according to the situation in which it grows, the fronds being broadest
and strongest in the deepest water. The root is covered with woolly
fibres, and the frond is regularly forked.
One of the most interesting algæ of this order is the Turkey-feather
Laver (_Padina pavonia_), which is the only British representative of
its genus (see Plate VII.). Its very pretty fan-shaped fronds are of a
leathery nature, curved, fringed along the upper margin, and marked with
concentric lines. They often bear small leaflets, and are partially
covered with a powdery substance which renders them beautifully
iridescent when in the water. The root has woolly fibres, and the spores
are arranged in lines along the upper margin. This weed seems to be
confined to the south coast, where it may often be seen in the deeper
tide pools; though in some of the sandy bays of the Isle of Wight it may
be seen in shallow pools, and even in places left exposed to the air at
low tide.
The genus _Zonaria_ contains a British species (_Z. parvula_) that
covers the rocks in round patches; and though moderately common is not
very frequently seen by collectors on account of the fact that it grows
in the deep crevices of rocks at or near low-water mark. Its frond is
flat and membranaceous, more or less divided into lobes, without veins,
and rather obscurely divided into concentric zones. It is attached to
the rock by fibres that proceed from the under surface of the frond, and
the spores are arranged in clusters beneath the superficial cells.
_Cutleria multifida_, though not very abundant, is to be found on most
of our coasts; but since it grows almost exclusively beyond low-water
mark, it should be looked for on the beach after storms, or in the
fishermen’s nets. The frond is olive-green, fan-shaped, rather thick,
and irregularly divided into forked branches; and it has a beautifully
netted surface. The spore-cases may be seen scattered over the surface
of the frond as so many black dots, and the antheridia are elongated,
cylindrical bodies attached to tufted filaments on all parts of the
frond.
In the genus _Stilophora_ the root is discoid; the frond cylindrical,
hollow, and branched; and the spores arranged in clusters over the
surface. One species (_S. rhizodes_) is occasionally to be seen on the
south coast. It is of a yellowish colour, from six to twenty inches
long, and may be known by its long thread-like branches, with scattered,
forked branchlets, and by the wart-like projections of the stem which
contain the spores. This weed is often the source of some disappointment
to the collector, for it soon turns to a jelly-like mass when removed
from the water, and should therefore be mounted as soon as possible
after it has been collected.
The fennel-like _Dictyosiphon fœniculaceus_ is abundant in tide pools,
where it may be seen in its best condition during spring and early
summer. Its root is a small disc, the frond is tubular, thread-like and
branched, and the branches bear hooked branchlets. The spores are naked,
and distributed either singly or in clusters over the surface of the
frond.
Our next genus--_Punctaria_--contains a few British species with a
shield-shaped root, and a flat, membranous, undivided frond, without a
midrib, and having the spores disposed as minute dots over the surface.
A plantain-like species (_P. plantaginea_) has broad, leathery,
lanceolate fronds, of a dark olive-brown colour, usually from six inches
to a foot in length. Two other weeds--the broad-leaved _P. latifolia_ of
the tide pools, and the slender, tufted _P. tenuissima_, which is
parasitic on _Zostera_ and soe algæ, are sometimes regarded as mere
varieties of _P. plantaginea_.
In the genus _Asperococcus_ the root is shield-shaped, and the frond is
a membranous tubular sac of two distinct layers. The colour is pale
green, and the general appearance very similar to that of _Ulva_. The
spores are arranged in small oblong clusters which appear as dark dots
on the surface of the frond. _A. compressus_ has slightly swollen flat
fronds of a linear lanceolate form, tapering below. It grows in deep
water, but is often washed up during storms. A second species--_A.
Turneri_--has large, puffy, green fronds, contracted at intervals, and
grows in tufts on rocks between the tide-marks, being specially partial
to muddy shores. The genus also includes the prickly _A. echinatus_, the
long, thin fronds of which grow in dense tufts in deep water.
The last genus of the order is _Litosiphon_, a parasitic group
characterised by a cylindrical, cartilaginous, unbranched frond, with
scattered, naked spores. A very small species (_L. pusillus_) with
tufted green fronds grows parasitic on the fronds of _Chorda_ and the
stems of _Laminaria_. It is only two or three inches long, has a
reticulated surface, and is covered with minute jointed fibres. A still
smaller species (_L. laminariæ_), seldom exceeding half an inch in
length, forms brown tufts on _Alaria_, and the rounded apex of its frond
is covered with minute fibres.
The order _Laminariaceæ_ contains olive, inarticulate algæ, mostly of
large size, and generally growing in deep water beyond the tide-marks.
Their spores are superficial, either covering the whole surface of the
frond or collected into indefinite cloudy patches.
[Illustration: FIG. 268.--_Laminaria bulbosa_]
[Illustration: FIG. 269.--_Laminaria saccharina_]
The typical genus (_Laminaria_) is characterised by flat leathery,
ribless fronds, either simple or cleft, and supported on a stem which is
often very thick and strong. The old laminæ fall off every year, and are
replaced by new fronds. The well-known Tangle or Sea Girdle (_L.
digitata_), is a very common species on the rocks just beyond low-water
mark. It has a very thick, solid, cylindrical stem, and an oblong
leathery frond which is entire when young but deeply cleft later. Small
specimens may be found just above low-water mark, but fine large ones
are commonly washed up on the beach. Although this weed may not be
regarded as an acquisition from the collector’s point of view, it will
generally repay a careful examination, as it frequently bears rare
parasitic species. The other common species are the Furbelows (_L.
bulbosa_), known by its flat stem with waved margin, oblong frond cleft
into narrow strips, and the hollow bulb or tuber just above the root;
and the Sugared Laminaria (_L. saccharina_) characterised by a round
solid stem, and a lanceolate, entire, membranous frond. The last species
is the one most commonly used by the sea-side cottager as a weather
indicator.
[Illustration: PLATE VIII.
SEA-WEEDS
1. Chorda filum
2. Fucus vesiculosus
3. Fucus canaliculatus
4. Delesseria (Maugeria) sanguinea
5. Rhodymenia palmata
6. Chondrus crispus
7. Ulva lactuca]
[Illustration: FIG. 270.--_Alaria esculenta_]
_Alaria esculenta_ is an edible species known as the Badderlocks in
Scotland, and also locally as the Henware, Honeyware, and the Murlins.
It has a fibrous root, and a stalked, lanceolate, entire frond with a
distinct midrib throughout. The stem is winged with finger-like
leaflets, in which the spores are arranged in oblong clusters.
In the genus _Chorda_ the frond is a simple, cylindrical tube, divided
internally by numerous transverse membranes, and the spores are
distributed over the surface. The commonest species is _C. filum_ (see
Plate VIII.), the frond of which is very slimy, and often from ten to
twenty feet in length. In its young state it is covered with gelatinous
hairs, but these are worn off as the plant develops. A smaller species
(_C. lomentaria_) is sometimes found on our shores. Its fronds are
constricted at intervals, taper at the tip, and grow in tufts. It is
seldom more than a foot long, and is not of a slimy nature.
[Illustration: FIG. 271.--_Sporochnus pedunculatus_]
The _Sporochnaceæ_ have inarticulate, thread-like fronds, and the spores
are contained in oblong, stalked receptacles, each of which is crowned
with a tuft of slender jointed filaments. The typical genus contains
only one British species--_Sporochnus pedunculatus_--and even that is by
no means common. It is, however, a very pretty weed of a delicate
texture and pale olive-green colour. Its stem is long and slender,
pinnately branched, and the branches bear numerous small thread-like
tufts.
The same order contains the genus _Desmarestia_, in which the frond is
long and narrow, thread-like or flattened, with a tubular jointed
thread running through it. Young specimens have marginal tufts of
branching filaments. The species decay very rapidly after removal from
the water, and should therefore be dried and mounted as quickly as
possible. _D. ligulata_, so named from the flat, strap-like frond, is
common on all our coasts. It is pinnately branched, and all the branches
and branchlets taper towards both ends. _D. viridis_ has a cylindrical,
thread-like and freely-divided frond, with opposite branches and
branchlets. It occurs more commonly on the northern shores.
[Illustration: FIG. 272.--_Desmarestia ligulata_]
The last order of olive-spored weeds is the _Fucaceæ_, some species of
which are so abundant between the tide-marks, from high-water to
low-water levels, that they form a very important characteristic of our
shores. They are mostly large, tough, and leathery weeds, without
joints, and the spores are contained in spherical receptacles embedded
in the substance of the frond.
In the typical genus--_Fucus_--the root is a conical disc, and the frond
flat or compressed and forked. Most of the species are furnished with
one-celled air-vessels in the substance of the frond, and these serve to
buoy up the plants and keep them more or less erect when submerged. The
spore-receptacles are usually embedded near the tips of the branches,
but are sometimes borne on special branches or shoots. They are filled
with a slimy mucus and contain a network of jointed filaments. The weeds
are very hardy, capable of withstanding long exposures to air and sun,
and are sometimes to be found _above_ high-water mark, where they are
watered only by the spray of the waves for a brief period at intervals
of about twelve hours. Although they are not usually looked upon as
ornaments in the collector's herbarium, they will repay examination for
the tufts of smaller and more beautiful weeds to which they often give
attachment and shelter.
Four species are common on our coasts, and these may be readily
distinguished by the most cursory examination. The Serrated Wrack (_F.
serratus_) has a flat, forked frond with toothed edges and a strong
midrib, ranging from one to four feet long, and no air-vessels. The
Knotted Wrack (_F. nodosus_--Plate VII.) may be known by its flattened,
thick and narrow frond, without a distinct rib, from one to five feet
long. The branches are narrow at the base, pointed at the tip, and are
jointed to short projections on the main stem; and both these and the
main stem have very large oval air-vessels. The spore-receptacles are
mounted on slender stalks which arise from projections on the branches,
and are of a bright yellow colour when mature. This species does not
grow so near to high-water mark as do the others. Another species, the
Twin-Bladder Wrack (_F. vesiculosus_--Plate VIII.)--is abundant
everywhere along the coast, and is largely used by agriculturists both
as manure and as fodder for cattle. The frond is flat, with a distinct
midrib, and a non-serrated edge. Air-vessels are not always present, but
when they are they usually occur in pairs, one on each side of the
midrib, and are globular in form. The spore-receptacles are situated at
the tips of the branches, are full of mucus, and are frequently forked.
The last of the common species is the Channelled Wrack (_F.
canaliculatus_--Plate VIII.), distinguished by a narrow frond, rounded
on one side and channelled on the other. It has no midrib or
air-vessels, and the fruit is contained in forked receptacles at the
tips of the branches. This is the smallest of the genus, and may be
found at all levels between the tide-marks. Stunted specimens may also
be seen in situations where they are never submerged, but watered only
by the spray of the highest tides.
[Illustration: FIG. 273.--_Himanthalia lorea_]
The genus _Himanthalia_ provides us with a single species (_H. lorea_)
which is very peculiar on account of the small size of the frond as
compared with the enormous dimensions of the spore-receptacles. The
young frond is a pear-shaped sac which soon becomes flattened into a
hollow disc. This disc then becomes solid, and concave above, and from
its centre there arises a bi-forked, strap-like receptacle that often
reaches a length of three or four feet, and may be mistaken for the
frond of the weed by those who do not take the trouble to examine it.
This weed is commonly known as the Sea Thong.
Belonging to the genus _Cystoseira_ we have a few well-known weeds with
conical disc-roots, and shrubby fronds with woody stem and alternate
branches. The air-cells are in the substance of the frond, and the
spore-receptacles at the tips of the branches. One of the species (_C.
ericoides_) is of a heath-like habit, with a short, woody stem, and
slender branches bearing hooked, leaf-like branchlets. Its air-cells are
small, and are arranged singly near the tips of the branches; and the
spore-receptacles are cylindrical, with hooked points. This weed is
common on the south and west coasts, and may be readily distinguished by
the beautiful iridescence it displays when in the water. _C. fibrosa_ is
very similar in general form, but is larger, and the air-vesicles are
more conspicuous. It is not iridescent when in the water. A third
species is named _C. granulata_ from the rough and knobby appearance of
the stem, due to numerous oval projections, from some of which spring
the slender, much-divided branches. The air-vesicles are arranged in
groups of two or three, and the spore-receptacles are at the ends of the
branchlets. Our last example is _C. fœniculacea_, found on the south
coast only, and readily distinguished by the numerous blunt spines that
cover its long branches. The air-vesicles are narrow and pointed, and
situated just below the forkings of the branchlets.
[Illustration: FIG. 274.--_Cystoseira ericoides_]
We conclude our _résumé_ of the British sea weeds with a short
description of the Podded Sea Oak (_Halidrys siliquosa_), which grows in
the tide pools from high-water to low-water mark, the specimens
inhabiting the shallow pools being only a few inches long, while those
that grow in deep water often reach a length of three or four feet. It
is an olive, shrub-like weed, with a conical, disc-like root that
adheres very firmly to the rock, and a pinnately-branched frond with
leaf-like branchlets. The air-vesicles are cylindrical and pod-like,
divided internally into about ten cells, and the spores are contained in
globular receptacles at the tips of the branchlets.
The young algologist will probably meet with many difficulties in his
attempts to classify his sea weeds and name the various species in his
collection. In dealing with an unknown weed we strongly recommend him to
first determine the order to which it belongs. The genus should next be
settled; and then, if possible, the species. It must be remembered,
however, that he who has made himself acquainted with the principles of
classification has done good work, and that it is far better to be able
to arrange the weeds into properly-classified groups than to merely
learn the names of the different species without regard to the relations
which they bear to one another. The following table will probably assist
the reader in the determination of the orders, but it must be remembered
that a microscope will often be necessary for the examination of the
spores and the minute structure of fronds.
CLASSIFICATION OF SEA WEEDS
=A.= =Chlorospermeæ=--Green-spored weeds. Fronds usually
grass-green, and filamentous or membranous.
1. _Confervaceæ_--Frond thread-like, composed of cylindrical
cells placed end to end. Spores very minute, formed
within the cells.
2. _Ulvaceæ_--Frond grass-green or purple, flat or tubular.
Spores minute, ciliated, formed in the cells of the
frond.
3. _Siphonaceæ_--Frond a single, thread-like, branching cell,
or a spongy mass of many such cells.
=B.= =Rhodospermeæ=--Red-spored weeds. Spores in globular
conceptacles. Tetraspores (four-clustered spores) in
globular or cylindrical cells. Frond red, reddish
brown, or purple.
4. _Ceramiaceæ_--Frond thread-like, jointed, one-siphoned, and
more or less covered with a layer of cortical cells.
Spores grouped in transparent, membranous sacs,
sometimes surrounded by a whorl of short branchlets.
5. _Spyridiaceæ_--Frond thread-like, jointed, one-siphoned,
more or less covered with small cells. Spores formed in
the upper cells of branched, jointed, radiating
threads, enclosed in a cellular membrane in external
conceptacles.
6. _Cryptonemiaceæ_--Frond more or less cartilaginous, composed
of numerous jointed threads compacted by gelatine.
Spores grouped without order in internal cells or in
external conceptacles.
7. _Rhodymeniaceæ_--Frond inarticulate, membranaceous, composed
of polygonal cells, the surface cells forming a
continuous layer. Spores in beaded threads in external
conceptacles.
8. _Wrangeliaceæ_--Frond inarticulate, thread-like, traversed
by a jointed tubular axis. Spores formed in the
terminal cells of clustered, branching, naked threads.
9. _Helminthocladiæ_--Frond cylindrical, gelatinous, composed
of filaments imbedded in gelatine. Spores formed on
branching, radiating threads that are enclosed in the
frond without conceptacles.
10. _Squamariæ_--Frond lichen-like, rooted by under surface,
composed of _vertical_ filaments imbedded in firm
gelatine. Spores in beaded threads in wart-like
projections.
11. _Spongiocarpeæ_--Frond cylindrical, branching,
cartilaginous, composed of netted filaments imbedded in
firm gelatine. Spores large, in radiating clusters in
wart-like excrescences.
12. _Gelidiaceæ_--Frond cartilaginous, inarticulate, composed
of hair-like filaments. Spores attached to slender
threads in internal conceptacles.
13. _Sphærococcoideæ_--Frond leaf-like or thread-like,
inarticulate, cellular. Spores formed in beaded threads
in external conceptacles.
14. _Hapalidiaceæ_--Frond minute, calcareous, composed of a
single layer of cells.
15. _Corallinaceæ_--Frond calcareous. Spores in tufted threads
at the bases of the conceptacles.
16. _Laurenciaceæ_--Frond rounded or flattened, branching,
inarticulate, cellular. Spores in external oval or
globular conceptacles. Tetraspores irregularly
scattered over the branches.
17. _Rhodomelaceæ_--Frond leafy, thread-like, or jointed,
composed of polygonal cells. Spores in external
conceptacles. Tetraspores in distorted branchlets or in
receptacles.
=C.= =Melanospermeæ=--Olive-spored weeds. Frond tough, leathery.
Spores in globular cavities in substance of frond.
18. _Ectocarpaceæ_--Frond jointed, thread-like. Spores attached to
or imbedded in branchlets.
19. _Chordariaceæ_--Frond gelatinous or cartilaginous, composed of
interlacing vertical and horizontal filaments. Spores
internal, attached to the filaments.
20. _Dictyotaceæ_--Frond inarticulate. Spores superficial, arranged
in definite spots or lines.
21. _Laminariaceæ_--Frond inarticulate. Spores covering the whole
frond or in cloud-like patches.
22. _Sporochnaceæ_--Frond inarticulate. Spores attached to jointed
filaments which are either free or compacted.
23. _Fucaceæ_--Frond inarticulate, large and tough. Spores in
globular cavities.