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134
THE MARINE ALGÆ OF NEW ENGLAND.
straight or falcate, sharply serrate, especially on the lower side, and the opposing
pinna pinnately divided or compound; pinnæ nearly at right angles to the axis,
apices acute; tetraspores borne in dense ellipsoidal cluster either at the ends of the
simple pinnæ or on the serrations and tips of the compound pinnæ; tetrasporic
masses interspersed with monosiphonous incurved branches; favellæ in similar
position to the tetraspores, nearly concealed by the large, incurved, usually serrate
divisions of the involucre.
On algæ, especially on stems of Laminaria, below low-water mark.
Common north of Boston; Thimble Islands, near New Haven, and dredged off Block
Island, Prof. Eaton.
A common and characteristic alga of our northern coast, extending through Greenland to the northern
coast of Europe, and also found in the North Pacific. The present species, together with Euthora
cristata and Delesseria sinuosa, form the greater part of the specimens collected for ornamental
purposes by ladies on the Northern New England coast. P. serrata, when dried, is usually very dark
colored, unless it has previously been soaked for some time in fresh water, and it does not adhere well
to paper unless under considerable pressure. It cannot be mistaken for any other species growing on
cur coast. Whether it is a variety of P. plumosa is a question about which writers do not agree, but,
although in this connection our form has been kept as a distinct species, it is highly probable that it is
really nothing more than a coarser northern form of P. plumosa. The typical form of P. plumosa is
certainly unknown in New England. The type is more slender, and the pinnæ are pectinate, not serrate.
The position of the fruit is the same, the principal difference being in the more strongly marked
involucre of the favellæ and in the tetraspores, which are borne on densely fastigiate branches, which
have no cortications, and some of which are incurved and project beyond the general sporiferous mass.
In P. plumosa the tetraspores are also borne on the tips of monosiphonous branches, but they are not
densely conglomerate, nor are the projecting incurved ramuli prominent. The present species is very
rare south of Cape Cod, being known in only two localities and in a much reduced form.
CERAMIUM, Lyngb.
(From κεραµιος [keramios], a small pitcher.)
Fronds filiform, dichotomous or occasionally subpinnate, monosiphonous, composed
of a series of large ovate or quadrate cells, with bands of small corticating cells at
the nodes, and in some species also extending over the internodes; antheridia
forming sessile patches on the upper branches; tetraspores tripartite, formed from
the corticating cells; cystocarps (favellæ) sessile at the nodes, usually involucrate.
A universally diffused and easily recognized genus, of which, however, the species are by no means
easily recognized. The genus is distinguished by the monosiphonous, dichotomous frond, with bands of
small corticating cells at the nodes, or, in some cases, covering the internodes as well. The tips of the
filaments are forked and usually decidedly incurved, whence the generic name is derived. The apical
growth and formation of the cortex is fully detailed by Nægeli and Cramer in Pflanzenphysiologische
Untersuchugen, Part IV. The procarp in Ceramium is furnished with two trichogynes and a single
carpogenic cell formed from the cortical cells on the convex side of the