“ Fronds one fourth or half an inch in diameter, cireular or
slightly convex, sometimes greenish, but oftener of a dark
chestnut colour. After a time, they run together into a flat
spongy crust, of indefinite size. On the smooth face of a
rock exposed to the trickling of water, I found a sheet of it
upwards of a foot in diameter. When broken the crust appears
zoned within, so as to indicate the age of the plant,
each zone being equal to a year’s growth. A t this age, it is
always more or less stony, from the absorption of calcareous
matter.” — Carxn.
2. L itho nem a crustaceum Hass.
Plate LX V . Fig. 3.
Char. Crust very thin, widely spreading. Filaments attenuated
at the base, fastigiately branched above the middle.
Rivularia crustácea Carm. MS. R. Crustacea Harv. in
Hook. Br. Fl. p. 393.; also in Manual, p. 151.
Hah. On rocks exposed to the spray of cascades, in the
hill streams at Appin : Captain Carmichael.
“ Crust of no determinate extent, extremely thin and slimy,
black. Filaments one fourth of a line in length, attenuated
at the base, fastigiately branched above the middle of an
olive green colour.”— Carm.
This species, although decidedly congeneric with L . calcareum,
may at once be distinguished from it by the fastigiate
division of its filaments.
“ I f you detect any mistakes of mine, I rely on your superior knowledge
to excuse them; for who has ever avoided errors in the wide-
extended field of Nature? Who is furnished with a sufiicient stock of
observations ? I shall be thankful for your friendly corrections, I have
done what I could myself.”— Linnæus to Haller.
F am . XV. NOSTOCHINEÆ.
The Nostochineoe form one of the most natural and beautiful
of the families of freshwater Algæ. The filaments are
simple, of uniform diameter, elegantly moniliform, resembling
strings of pearls, in the highest degree flexible, and of exceeding
lubricity. The species of which it is composed
naturally arrange themselves into two divisions : in the one
the filaments are free, and in the other imbedded in a mucous
matrix, which sometimes assumes a definite form.
A t intervals, in the course of the filaments, are observed
cells larger than those which compose the thread itself: these,
in the genus Anahaina are more or less of an oval or elongated
form ; while in the genus Nostoc they are exactly spherical.
They are generally supposed to be connected with reproduction;
but hitherto no precise observations have been made
upon them. In most, and perhaps in all the species of Nostoc,
many of these enlarged cells are scattered singly and detached
throughout the mucous matrix : they have doubtless
become separated from the filaments of which originally they
formed a link.
I f a Nostoc in the first period of its developement be examined,
it will be observed to consist of a single moniliform
thread, short, and but little curved, immersed in a mucous
nidus. In each of the fully developed specimens of most of
the Nostocs, however, threads innumerable present themselves.
Now the question arises, in what way are those threads multiplied
? First, and chiefly I conceive, by the separation or dislocation
of the enlarged cells, whereby each filament is divided
into other shorter filaments ; and in the second place, probably
by the growth of those vesicles themselves; but on this point
nothing positive is known. Independently of these two modes
of multiplication of the threads in each frond, no other conceivable
method exists. The filaments in every example of a