basis of cellulose, and in some cases readily breaks up into
a definite number of plates, fitting into one another like
the plates of the carapace of a tortoise; it is, moreover,
often finely sculptured or coarsely ridged and flanged. Two
grooves are a constant feature of the family, one running
transversely and anoiher longitudinally. In these grooves
lie two c;lia, attached at the point of meeting on the dorsal
surface. The protoplast is uninucleate and vacuolate,
and contains chromatophores of a brownish colour. It is
not clear that FIG. 4.--Phaeophyceae, variously magnified.
A. Halopteris, apical region.
B. Chordaria sp., apical region showing so-called trichothallic growth.
C. Dictyota sp., apical cells immediately after dichotomy.
D. Cutleria sp., margin of thallus showing trichothallic growth.
E. Halidrys, apical depression with leading cell.
F. Macrocystis sp., tubular elements from the
medulla, with sieve-like transverse walls.
G. Laminaria sp., hyphae with trumpet-like ends also from medulla.
H. Elachistea sp., Plurilocular sporanges.
K. Ectocarpus sp., unilocular sporange.
L. Ectocarpus siliculosus, female gamete surrounded
by male gametes a, b, c, d, e, stages of conjugation.
M. Cutleria multifida. a, antherozoids, b, a female gamete.
N1. Fucus vesiculosus, young oogonium.
N2. Fucus vesiculosus, discharge of eight oospheres from oogonium
O. Laminaria sp., sporanges among paraphyses.
P. Dictyota dichotoma, a sorus of oogonia.
Q. Dictyota dichotoma, part of a sorus of antheridia.
(A, B, C, D, E, H, L, M, P, from Engler and Prantl, by
permission of Wilhelm Engelmann; F, G, K, O, from Oltmanns,
by permission of Gustav Fischer; Q. from The Annals of
Botany, by permission of the Clarendon Press; N1, N2,
from Hauck, Meeresalgen, by permission of Eduard Kummer.)
the brown colouring matter which is added to chlorophyll
is identical with phycophaein: two varieties of it have
been termed phycopyrrin and peridinine. Certain species,
such as Gymnodinium spirale, are colourless and therefore
saprophytic in their method of nutrition. Multiplication
takes place in some cases by the endogenous formation of
zoospores, the organism having come to rest; in others by
longitudinal division, when the organism is still motile.
No method of sexual reproduction is known with certainty.
The Cryptomonadaceae also are unicellular, and live free or in
colonies. Each cell contains a flattened chromatophore of a
brown or yellow colour. Hydrurus forms a branched gelatinous
colony attached to stones in mountain streams. Chromophyton
forms an eight-celled colony. Both plants multiply solely by
means of zoospores. The Cryptomonadeae and Chromulineae are
motile through the greater part of their life. Cryptomonas,
when dividing in a mucilage after encystment, recalls the
condition in Gloeocystis. In Synura and Chromulina the
cells form a spherical motile colony, recalling Volvocaceae.
Chromulina is uniciliate, and is contained in a hyaline
capsule. Like the Peridiniaceae, the Cryptomonadaceae have
been included among Flagellata. They have no close affinity
with Euphaeophyceae. Such colonial forms as Hydrurus
and Phaeocystis are supposed, however, to indicate
a stage in the passage to the multicellular condition.
Diatomaceae have long been recognized as plants. Together
with Peridiniaceae they constitute the bulk of marine plankton,
and thus play an important part in the support of marine
animal life. They exhibit striking adaptations in these
circumstances to the floating habit. (See DIATOMACEAE.)
A census of Phaeophyceae is given below:--
(1) Cyclosporinae (Fucaceae)--4 families, 32 genera, 347 species.
(2) Tetrasporinae (Dictyotaceae)-- 1 family, 17 genera, 130 species.
(3) Phaeozoosporineae (Phaeosporeae)--24 families, 143
genera, 571 species. (De Toni's Sylloge ALgarum.)
(4) Peridiniales---3 families, 32 genera, 167 species.
(5) Cryptomonadaceae (including Chrysomonadaceae)
--2 families, 28 genera, 50-60 species.
(6) Bacillariales (Diatomaceae)--about 150
genera and 5000 species, fossil and recent.
(Engler and Prantl's Pflanzenfamilien)
IV. RHODOPHYCEAE, or FLORIDEAE.--The members of this
group are characterized by the possession of a red colouring
matter, phycoerythrin, in addition to chlorophyll. There is,
however, a considerable amount of difference in the shades
of red which mark different species. The brightest belongs
to those species which grow near low-water mark, or under
the shade of larger algae at higher levels; species which
grow near high-water mark are usually of so dark a hue that
they are easily mistaken for brown seaweeds. Rhodophyceae
are mostly marine, but not exclusively so. Thorea,
Lemanea, Tuomeya, Stenocladia, Batrachospermum, Balbiania
are genera belonging entirely to fresh water; and Bangia,
Chanitransia, Caloglossa, Bostrychia and Delesseria
contain each one or more freshwater species. Most of the
larger species of marine Rhodophyceae are attached by means
of a disc to rocks, stones or shells. Many are epiphytic
on other algae, more especially the larger Phaeophyceae and
Rhodophyceae. As in the case of epiphytic brown seaweeds,
the rhizoids of the epiphyte often penetrate the substance
of the supporting alga. Some Red Algae find a home in the
gelatinous substance of Flustra, Alcyonidium and other
polyzoa, only emerging for the formation of the reproductive
organs. Some are perforating algae and burrow into the
substance of molluscan shells, in company with certain Green
and Blue-green Algae. Some species belonging to the families
Squamariaceae nnd Corallinaceae grow attached through their
whole length and breadth, and are often encrusted with
lime. The forms which grow away from the substratum vary
greatly in external configuration. In point of size the
largest cannot rival the larger Brown Algae, while the majority
require the aid of the microscope for their investigation.
No unicellular Rhodophyceae are known, although a flagellate
organism, Rhodomonas, has recently been described as possessed
of the same red colouring matter. If the sub-group, Bangiaceae,
be excluded, they may be said to consist exclusively of branched
filaments. Growth in these cases takes place by means of an
apical cell, from which successive segments are cut off by means
of a transverse wall. The segment so cut off does not usually
divide again by means of a transverse wall, nor indeed by a
longitudinal wall which passes through the organic axis of the
cell. New cells may be cut off laterally, which become
the apical cells of branches. When the new cells grow no
further, but constitute a palisading round the central cell
covering its whole length, the condition is reached which
characterizes the species of Polysiphonia, the "siphons" of
which may be regarded as one-celled branches. To the law that
no subsequent transverse division takes place in segments cut
off from the apical cell, there seem to be two exceptions:
first, the calcareous genus Corallinia, in the pliable
joints of which intercalated division occurs; and, second,
the Nitophylleae, in which, moreover, median longitudinal
division of axial cells is said to occur. Like the Fungi,
therefore, the Red Algae consist for the most part of branched
filaments, even where the thallus appears massive to the eye,
and, as in the case of Fungi, this fact is not inconsistent
with a great variery of external morphology. In the great
majority the thallus is obviously filamentous, as in some
species of Cillithamnion. In other species of that genus
an apparent cortication arises by the downward growth of
rhizoids, which are retained within the gelatinous wall of the
axial cells. in Batrachospermum the whole system of branches
are retained within a diffluent gelatinous substance derived
from the outer layers of the cell-walls. In other cases the
mucilage is denser and the branches more closely compacted
Helminthora.) In such cases as Lemanea, the terminal
cells of the lateral branches form a superficial layer which
has all the appearance of a parenchyma when viewed from the
surface. In Champia and allied genera, the cylindrical axis
is due not to the derivatives of one axial filament, but of
several, the growth of which is co-ordinated to form a septated
tube. The branching of the thallus, which meets the eye
in all these cases, is due to the unlimited growth of a few
branches. When such a lateral branch overtops the main axis
whose growth has become limited, as in Plocamium and Dasya,
a sympodium is formed. For the most part the branching is
monopodial. Besides the differentiation into holdfast and
shoot, and into branches of limited and branches of unlimited
growth, there appear superficial structures of the nature of
hairs. These are for the most part long, thin-walled,
unicellular and colourless, and arise from the outer cells
of the pseudo-cortex, or from the terminal cells of branches
when the filaments are free. Among Rhodomelaceae, hair-like
structures of a higher order are known. These arise from
the axial cell, and are multicellular and branched. They
soon fall off, and it is from the persistent basal cell that
the branches of unlimited growth arise. Upon them also the
reproductive organs arise in this family. It is not surprising,
therefore, that they have been regarded as the rudiments of
leaves. In Iridaea the thallus is an entire lamina; in
Callophyllis a lobed lamina; in Delesseria it is provided
with midrib and veins, simulating the appearance of a leaf
of the higher plants; in Constantinea the axis remains
cylindrical, and the lateral branches assume the form of
leaves. In the compact thalli a secondary development
often takes place by the growth of rhizoid-like internal
filaments. They present a hypha-like appearance, running
longitudinally for considerable distances. It is not difficult
in such compact species to distinguish between superficial
cells, whose chief function is assimilation, subjacent cells
charged with reserve material, and a core of tissue engaged
in the convection of elaborated material from part to part.
An interesting feature of the minute anatomy of Euflorideae,
as the Red Algae, exclusive of the Bangiaceae, have been
termed, is the existence of the so-called Floridean pit.
When a cell divides it is found that there remains in the
middle of the new wall a single large circular pit, which
persists throughout the life of the cells, becoming more and
more conspicuous with the progress of the thickening of the
wall. These pits serve to indicate the genetic relationship
of adjacent cells, when they form a compact pseudo-parenchyma,
notwithstanding the fact that somewhat smaller secondary pits
appear later between any contiguous cells. Protoplasmic continuity
has been observed in the delicate membrane closing the pit.
Vegetative multiplication occurs only sparingly in Rhodophyceae.
Melobesia callithamnioides gives rise to multicellular
propagula; (Griffithsia corallina is said to give rise
to new individuals, by detaching portions of the thallus
from the base of which new attachment organs have already
arisen. The spores of Monospora are by some regarded as
unicellular propagula. Reproduction is both asexual and
sexual. It is noteworthy that although all the members of
the group are aquatic no zoospores are produced, a negative
character common to them and the Blue-green Algae. As a rule
the asexual cells, and the male and female sexual cells arise
upon different plants, so that the species may be said to be
