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REPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 121
species of Callithamnion, as here understood, the procumbent filaments are wanting or imperfectly
developed, and the erect filaments either remain throughout monosiphonous, that is composed of single
rows of cells, or become corticated by the growth of descending filaments, which proceed either from the
base of the branches or from the cells of the main filaments. The false cortication formed by the
interlacing of these filaments is precisely analogous to what is found in some species of Ectocarpus and
related genera. The filaments in Callithamnion are either all indeterminate in growth, or else, as in the
subgenus Antithamnion, they are of two kinds; the main filaments being indefinite and the branches
definite, so that we have indefinitely elongating stems clothed with short, definite branches, or, to use
the expression of Nægeli, with leaves. The antheridia are generally in the form of short tufts of hyaline
cells, situated on the upper branches. In the present genus it is not rare to find species in which
antheridia, cystocarps, and tetraspores are borne on the same individuals, a union rarely to be seen in
the Florideæ. The cystocarps are often binate, which is easily understood if one considers the structure
of the procarp, which is formed as follows: One of the cells of the young branches enlarges and is then
divided by partitions parallel to the length of the branch into a central or axial cell and a number of
peripheral cells, generally four. One of the peripheral cells is then divided into an upper and one or
more lower cells by a transverse partition, and the upper cell then loses its color and grows upwards
into a very long trichogyne. The antherozoids unite with the tip of the trichogyne, and the fertilizing
influence is propagated through the trichogyne and the cells at its base to the two lateral peripheral
cells, which then enlarge and divide on opposite sides of the axis and form eventually a bipartite
favella. The tetraspores are either tripartite or cruciate. In the subgenus Seirospora there is a form of
non-sexual spore known as seirospores, in which at the extremity of the branches are formed tufts
composed of chains of oval bodies, each one of which is capable of germinating.
As is apt to be the case in a large genus, the species of Callithamnion are not well defined. Certain
groups of species are distinct, but writers are not agreed as to the limits of the species in each group. By
some a great many species are allowed which others regard as mere varieties. On our coast C. Baileyi,
C. byssoideum, C. corymbosum, and perhaps others might be indefinitely split up, but we have
preferred to adopt the opposite view. Within certain limits collectors may be expected to make out our
species of Callithamnion, but it must often happen that forms are found which cannot with certainty be
referred to any of the described species. That such forms are, as a rule, new species cannot be accepted,
but botanists having large sets of species of the present genus soon become very liberal in the
interpretation-of specific limitations.
SUBGENUS RHODOCHORTON, Næg.
Fronds composed of procumbent filaments, from which arise vertical monopodial
filaments; cortications wanting; tetraspores cruciate.
C. ROTHII, Lyngb. (Rhodochorton Rothii, Næg.—Thamnidium Rothii, Thuret, in Le
Jolis’s Liste des Algues Marines de Cherbourg, Pl. 5, Figs. 1-2.—C. Rothii, Phyc.
Brit., Pl. 120 b.)
Fronds forming indefinite patches half an inch high, vertical filaments slender,
naked below, bearing a few erect, appressed branches above, which become at the
time of fructification congested and corymbose, bearing at their tips cruciate
tetraspores; antheridia and cystocarps unknown.
Forming dense velvety patches on rocks between tide-marks.