trioecious. Numerous exceptions, however, occur. Thus in
Lemaneaceae asexual spores are unknown; in Batracho-spermum,
Bonnemaisonia and Polysiphonia byssoides both kinds of
sexual cells appear on the same plant; and in some cases the
asexual cells may occur in conjunction with either the male or
female sexual cells. The asexual cells are termed tetraspores
on account of the usual occurrence of four in each sporangium.
What may be termed monospores, bispores and octospores,
however, are not unknown. The sporangia may be terminal or
intercalated. When they are confined to special branches
such branches are spoken of as stichidia. The tetrasrores
may arise by the simultaneous division of the contents of a
sporangium, when they are arranged tetrahedrally, or they may
arise by two successive divisions, in which case the arrangement
may be zonate when the spores are in a row, or cruciate when
the second divisions are at right angles to the first, or
tetrahedral when the second divisions are at right angles to
the first and also to one another. Tetraspores are at first
naked, but soon acquire a cell-wall and germinate without a
period of rest. The male sexual cells are produced singly
in the terminal cells of branches. They are spoken of as
spermaria. Great numbers of antheridia are usually crowded
together, when the part is distinguishable by the absence
of the usual red colour. In Polysiphonia they cover the
joints of the so-called leaves; in Chondria they arise
on flattened dishs; in the more massive forms they arise in
patches on the ordinary surface; in a few cases (Gracilaria,
Corallina, Galaxaura) they line the walls of conceptacle-like
depressions. The female sexual cell is represented by the
contents of a cell which is terminal on ordinary or specialized
branches. This is the carpogonium: it consists of a neutral
portion which contains a nucleus, but in which no oosphere is
differentiated, and an elongated tubular portion known as the
trichogyne, into which the cytoplasm extends. Fertilization
is effected by the passive convection of a spermatium from
the antheridium to the trichogyne, to which it adheres,
and to which it passes over its nucleus through an open
communication set up at the point of contact. The nucleus
then passes down the trichogyne and fuses with that of the
eeg. This fusion has been observed by Wille in Nemalion
multifidim, and by Schmidle in Batrachospermum. It is
singular that in the last-named species two nuclei occur
regularly in the spermatium. The ventral portion of the
carpogonium may be imbedded deep in the thallus in the
massive species; the trichogyne, however, always reaches the
surface. The first effect of fertilization is the occlusion
of the trichogyne from the fertilized carpogonium. The
subsequent course of development is characteristic of the
Florideae. The carpogonium germinates forthwith, drawing
its nourishment almost wholly from the parent plant. The
ultimate product in all cases is a number of carpospores, but
before this stage is reached the development is different in
different subgroups. In Batrachospermum filaments arise
from the carpogonium on all sides; in Chantransia and
Scinaia on one side only; in Helminthora the filaments
are enclosed in a dense mucilage; in Nemalion, prior to
the formation of the filaments, a sterile segment is cut off
below. In all these cases, however, the end-cells of the
filaments each give rise to a carpospore, and the aggregate
of such sporiferous filaments is a cystocarp. Again, in the
family of the Gelidiaceae, the single filament arising from
the carpogonium grows back into the tissue and preys upon
the cells of the axis and larger branches, after which the
end-cells give rise to carpospores and a diffused cystocarp is
formed. In the whole group of the Cryptonemiales the
parasitism becomes more marked still. The filaments arising
from the carpogonia grow into long thin tubes, which fuse
with special cells rich in protoplasm contents; and from
these points issue isolated tufts of sporogenous filaments,
several of which may form the product of one fertilized female
cell. In Naccaria, one of the Gelidiaceae, it is observable
that the ooblastema filament, as the tube arising from the
fertilized carpogonium has been called, fuses completely with
a cell contiguous to the carpogonium before giving rise to
the foraging filaments already referred to. This is also
the case among Cryptonemiales. In a whole series of Red
Algae, the existence or a highly specialized auxiliary cell
in the neighbourhood of the carpogonium is a characteristic
feature. In the Gigartinales it is already differentiated
previous to fertilization; in Rhodymeniales it arises
subsequent to fertilization. In the Gigartinales, the
filaments which arise from the auxiliary cell may spread and
give rise to isolated tufts of sporogenous filaments, as in the
Cryptonemiales. In the Rhodymeniales a single tuft arises
directly from the auxiliary cell. The carpospores are in
all cases bright red naked masses of protoplasm when first
discharged. They soon acquire a cell-wall, and germinate
without a period of rest. When the cystocarps or segments
of cystocarps are formed in the substance of a thallus, the
site is marked merely by a swelling of the substance. When
the cystocarp is produced externally, it may form a berry-like
mass without an envelope, in which case it it known as a
favella. In Rhodomelaceae there is a special urn-shaped envelope
surrounding the sporogenous filaments. This is a ceramidium.
The attachment of the cell of an ooblastema filament to a
cell of the thallus may be effected by means of a minute
pore, or the two cells may fuse their contents into one
protoplasmic mass. In the latter case, and especially
where the union is with a special auxiliary cell, it is of
importance to know what happens to the nuclei of the fusing
cells. Schmitz was of opinion that in the cases of open
union there occurred a fusion of nuclei similar to that
which occurs in the sexual union of two cells. He founded
his generalization to a large extent upon the observation
that in Gloeosiphonia capillaris two cells completely
fuse, and that only one nucleus can be detecteo in the fused
mass. Oltmanns has recently re-investigated the phenomena in
this plant, among others, and has shown that the nucleus of
the cell which is being preyed upon recedes to the wall and
gradually atrophies. The nucleus of the ooblastema filament
dominates the FIG. 5.--Rhodophyceae, variously magnified.
A. Polysiphonia sp., apical region showing
leading cell and cutting off of pericentral cell.
B. Polysiphonia sp., transverse section through
a branch, and at a, mother-cell of tetraspores.
C. Lomeittaria sp., apex showing growth in length
through coordinated growth of many filaments.
D. Delesseria sp., showing apical region with leading cell.
E. Chrysymenia uvaria, axis with swollen leaf-like appendages.
F. Polyzonia sp., branch with leaf-like branches of limited growth.
G. Collithamnson sp., tetrasporangium with spores arranged in a tetrad.
H. Corallina sp., tetrasporangia with zonate arrangement of tetraspores.
K. Nemalion sp., carpogonial and antheridial branches.
L. Batrachospermum sp., trichogyne with spermatia
attached; carpospores arising from fertilized carpogonium.
M. Polysiphonia sp., antheridium.
N. Constantinea sp., with flattened leaf-like appendages.
O. Dudresnaya coccinea, fusion of ooblastema filaments with auxiliary
cells; a is an axial cell in transverse section with four appendages.
P. Callithamnion corymbosum, a joint cell with
carpogonial branch and a, b, two auxiliary cells.
Q. Callithamnion corymbosum, fusion of products of fertilization with
auxiliary cells, the nuclei of which a and b retire to the wall.
R. Polysiphonia sp., section through young cystocarp.
(A, C, D, E, F, G, H, K, L, M, P, Q, from Oltmanns,
by permission of Gustav Fischer; B, N, O, R, from
Engler and Prantl, by permission of Wilhelm Engelmann.)
mass and from it all the nuclei of the carpospores are thus
derived. There thus seems to be no justification for
believing, as Schmitz taught, that a second sexual
act occurs in the life-cycle of these Florideae.
The Bangiales are a relatively small group of Red Algae,
to which much of the description now given does not apply.
Structurally they are either a plate of cells, as in Porphyra, or
filaments, as in Bangia. There is no exclusive apical growth,
and the cells divide in all directions. The characteristic
pit is also absent. Sexual and asexual reproduction prevail.
The male cell is a spermatium, but the female cell bears no
such receptive trichogyne as occurs in other Rhodophyceae.
After fertilization the equivalent of the oospore divides
directly to form a group of carpospores. There is thus a
certain resemblance to Euflorideae, but sufficient difference
to necessitate their being grouped apart. Fertilization by
means of non-motile spermatia and a trichogyne are known among
the Fungi in the families Collemaceae any Laboulbeniaceae.
A census of Rhodophyceae is furnished below:--
(1) Bangiaceae--4 families, 9 genera, 58 species.
(2) Nemalioninae--4 families, 33 genera, 343 species.
(3) Gigartininae--3 families, 54 genera, 409 species.
(4) Rhodymeninae--4 families, 92 genera, 602
species. (De Toni's Sylloge Algarum, 1897.)
Limits of the algae.
After this survey of the four groups comprised under Algae
it is easier to indicate the variations in the limits of the
class as defined by different authorities. To consider the
Cyanophyceae first, either the marked contrast in the method of
nutrition of the generally colourless Bacteriaceae to that of
the blue-green Cyanophyceae is regarded as sufficient ground for
excluding Bacteriaceae from algae altogether, notwithstanding
their acknowledged morphological affinity with Cyanophyceae,
or, in recognition of the incongruity of effecting such a
separation, the whole group of the Schizophyta --that is to
say, the Cyanophyceae in the narrow sense, together with
Bacteriaceae, is included or excluded together. Again,
while Conjugatae may be shut out from Chlorophyceae as an
independent group co-ordinate with them in rank, the Characeae
constitute so aberrant a group that it has even been proposed
to raise them as Charophyta to the dignity of a main division
co-ordinate with Thallophyta. Similarly, while Diatomaceae
may be excluded from among Phaeophyceae, though retained among
algae, the Cryptomonadaceae and Peridiniaceae, like Euglena
and other Chlorophyceae, may be excluded from Thallophyta
and ranged among the flagellate Protozoa. It is doubtful,
however, whether the conventional distinction between plants
and animals will continue to be urged; and the suggestion of
Haeckel that a class Protista should be established to receive
the forms exhibiting both animal and plant affinities has much
to recommend it on phylogenetic grounds. To adopt a figure,
it is probable that the sources from which the two streams of
life--animal and vegetable--spring may not be separable by a
well-defined watershed at all, but consist of a great level
upland, in which the waterways anastomose. Finally, while
Chlorophyceae and Phaeophyceae exhibit important affinities,
the Rhodophyceae are so distinct that the term ``algae'' cannot
be made to include them, except when used in its widest sense.
Phylogeny.
It has been well said that the attempt to classify plants according
