either undivided, hut furnished with numerous alternate lateral branches ; or
in’egidaiiy forked, and gradually dissipated in the bushy frond ; branches
long, simple or compound, much attenuated, more or less densely clothed
rvitii quadi-ifarious multifid branchlets, from one to two inches in length,
alternately divided. Eamuli setaceous, acute, slightly tapering at the base.
Tubercles abundant, forming a spherical sweUing in the middle of the
ramidi, one or more in each ramulus. Tetraspores oblong, divided by three
transverse lines, into four parts, vertically immersed among the cells of the
surfiice, dispersed through the smaller branches and ramuli. Substance
cartilaginous, soft, imperfectly adhering to paper. Colour a dull purplish-
pink, often pale ; becoming much darker in drying.
The genera Hypnea and Gracilaria are, as I have already
noticed in the remarks under Plate LXV., very closely allied to
each other, but the character derived from the tetraspores, there
pointed out, will not serve to distinguish them, for 1 have
since ascertained that annular tetraspores exist in most of the
Gracilarioe, as well as in Hypnea. If the two genera are to be
maintained we must look for other distinctions, and these may be
most readily found in the structure of the frond, the true Gra-
cilarim having an axis composed of very large cells ; the Hypneæ
having a more or less evident fibro-cellular axis, composed of
minute, elongated cells. The calibre of this axis varies greatly
in the different species, in some of which it exists like a thread ;
in others, as in the present species, it is of great size, and the
cells by which it is surrounded are of much smaller dimensions
than in the typical H. musciformis. Kützing, indeed, forms a
new genus, which he calls Gystodonium for our H. purpurascens.
In this step I am not disposed to follow him, because it appears
to me that the difference in structure is more one of degree, than
of kind ; and because the cirrhose habit of our var. S- indicates
a close relationship with the Hypneæ, most of which produce
similar tendrils.
Hypnea purpurascens is among the commonest of our Algæ,
very variable in appearance, and very widely dispersed through
the North Atlantic. If allowed to retain its place, it is the most
northern example of the genus, none others being found north
of the Mediterranean.
Kg. 1. H y p n e -V p u e p u k a s c e n s :— of the natural size. 3. Portion of a ramulus.
3. Section of a tubercle. 4. Tetraspores. 5. Cross section of the frond
6. Tlongitudinal semi-section of the same:—a l l )