The colour varies from pale yeUowish, in shaUow water, to various degrees
of livid purple, in deeper and more shaded situations. In fresh water the
plaut soon decomposes, giving out a pinkish dye of some brilliancy.
A very common plant, and one which, though tolerably constant
to a particular ramification, having long simple branches
springing from a simple stem, is yet subject to many modifying
causes, which affect its habit, and general appearance very considerably.
The variety /3, an excellent figure of which is given
by Dr. Greville, in his ‘ Crypt. Flora,’ differs extremely from the
normal form, represented in our plate. In it, tbe frond is often
an inch in diameter, and so much puckered and waved, that,
except in colour, it strongly resembles Enteromorpha intestinalis.
Yet this variation appears to arise solely from locality, being
always found where a strong stream rolls down.
Dumontia fiUformis is widely dispersed in the temperate zones,
and was found by Dr. Hooker, both in the Auckland group of
Islands, and at the Falklands. Throughout Europe it is extremely
common. There are several other species of the genus,
many of which are found in the Kamtschatkan seas, and along
the opposite coast of America. One of them, D. saccata, which
has a simple, bag-like frond, is found, if aU the plants which go
under this name belong to one species, in localities nearly as
widely apart as is D. fiUformis, occiu’rmg on the west coast of
America, and at the Cape of Good Hope. Anotlier species, D.
prismatica, J. Ag., inhabits the Indian Ocean. But the generic
characters of several of the reputed species, require examination,
and, probably, many will eventually lie removed to new genera.
The Dumontiæ are the most simple in structure of the Gastero-
carpeoe, in which they represent such plants as Enteromorpha,
Asperocoocus, &c. They are also found at a higher level than any
others of their family, some of them growing, as our common
one occasionally does, nearly at high water mark.
Kiitzing figures and describes tetraspores on this species, but I
have not had the good fortune to find them. The clustered
spores are common.
Fig. I . D u m o n t i a f i l i f o r m i s :—natural size. 2. Portion of the frond, shoiving
a front view of a cluster of spores, attached to the inner surface. 3. Lateral
view of the same cluster, and vertical section of the wall of the frond :—
magnified.