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180
THE MARINE ALGÆ OF NEW ENGLAND.
frond in the Melobesioid group is that given by Rosanoff in his work already referred to. According to
Bornet, however, the cystocarpic fruit of the Melobesiæ escaped the observation of Rosanoff, and what
the latter called cystocarps were only a form of the non-sexual or tetrasporic fruit. The tetraspores are
found in two different forms—either in hemispherical conceptacles, which have a single central orifice
of good size, at whose base the spores are borne around a central tuft of paraphyses, or else in
truncated conceptacles, whose flattened upper surface is perforated with numerous orifices, beneath
each one of which is a tetraspore, separated from its fellows by a large, colorless cell.
The fronds of the smaller species of Melobesia, as M. Lejolisii and M. farinosa, consist of two portions,
the basal and the cortical. The former consists of a single layer of cells, which arise from the division of
the spore into four cells and subsequent marginal growth. The cortical layer in the smaller species is
composed of small cells cut off by oblique partitions from the upper part of the basal cells. In the larger
species of Melobesia, more particularly those placed in the subgenus Lithophyllum, the cortical layer is
much more marked, and the cells of which it is composed seem to be arranged in lines which are curved
at the base, but are straight above and at right angles to the direction of growth. In some of the small
species of Melanesia certain of the basal cells elongate and swell at the summit, so that when seen from
above they look larger than the neighboring cells. Rosanoff applied to such cells the name of
heterocysts, a word badly chosen, since the heterocysts in the Nostochineæ, where the term was first
employed, cannot well be compared with the heterocysts in Melobesia. The conceptacles in all our
species of Melobesia are external. The form generally found is that which contains the tetraspores. Our
species all occur in Europe, and it is very probable that the remaining Northern European forms not
yet recorded with us will be found on further search.
a. Species small, growing on plants, basal stratum well marked, cortical layer
imperfectly developed.
M. LEJOLISII, Rosanoff. (M. membranacea, Aresch., in Agardh’s Spec. Alg.; Harvey,
Phyc. Brit., Pl. 347, in part.—M. farinosa, Kütz., Spec. Alg.; Le Jolis’s Liste des
Algues.—M. Lejolisii, Rosanoff, l. c., p. 62‚ Pl. 1, Figs. 1-12.)
Fronds thin and brittle, at first orbicular but soon densely confluent, forming scaly
patches of indefinite extent; heterocysts wanting, basal cells squarish, cortical cells
few and indistinct; tetrasporic conceptacles very numerous, approximate, flattenedconvex,
orifice ciliated; tetraspores four-parted; antheridia and cystocarps?
On leaves of Zostera.
Wood’s Holl, Mass.; common from Nahant northward; Europe.
A species which is certainly common on eel-grass on the northern coast and probably equally abundant
in Long Island Sound, although definite information on this point is wanting. This is the form which is
found in American herbaria bearing the name usually of M. farinosa or M. membranacea. The orbicular
character of the fronds soon disappears, as they are found in great numbers, and at an early stage
become confluent. The conceptacles are so numerous that at times very little of the fronds themselves
can be seen. The latter easily crumble and fall from the plant on which they are growing.
M. FARINOSA, Lam.x. (M. farinosa, Aresch., in Agardh’s Spec. Alg., non Le Jolis’s
Liste des Algues.—M. farinosa and M. verrucata? Harvey, in part.—M. farinosa,
Lam.x., in Rosanoff, l. c.‚ p. 69‚ Pl. 2, Figs. 2-13.)