m
J
m
But the evidence of which we are in possession would appear
greatly to preponderate in proof of the vegetable character
of the Diatomaceoe ; thus, putting aside their silicious constitution,
and the partitions in the cells : the filaments of the
Aleloseiroe do not differ in the least in their modes of developement
and growth from those of the Vesiculiferoe, nor indeed
do those of Fragilaria differ very essentially from the filaments
of the true Algæ ; in their reproduction, likewise, so
far as this has been ascertained, the Diatomaceoe correspond
with the Desmideæ, and perhaps with all the lower Algæ.
In support of their animal nature may be urged their
colour, which is different from that of all other undoubted
vegetable productions, and the silex of which they are principally
constituted. These arguments, however, are not conclusive,
nor are they of as much weight as those adduced in
proof of their vegetahility. It is probable that in this matter,
as in many other disputed points, the truth lies in the mean,
and that the Diatomaceoe are neither exclusively animal, nor
exclusively vegetable, hut of a nature intermediate.
Owing to the presence of silex, the most indestructible
of substances, the species of this family are frequently found
beautifully preserved in a fossil state, and often in amazing
quantities all over the world. In the arts, the powder which
they form has been employed for pohshing. Many of the
fossil species are identical with those now found in a recent
state.
Section i.
F xemà. filamentous.
A. Filaments cglindrical.
66. MELOSEIRA Ag.
Char. Filaments cylindrical, subulate. Cells divided in the
centre or bilocular, sometimes vesicular. Junction surfaces
o f the cells either rounded or truncate, plain or
striated.
Derivation. From gsXos, a member, and usipa, a chain.
The species of the genus Meloseira admit of division into
two subgenera. The first of these, the species of which are
chiefly marine, and to designate which the word Sphoerophora *
might be employed, are characterized by a peculiar form and
structure of the cells. The extremities of these are rounded,
and each contains, at first, one, and afterwards two spherical
vesicles or globules, divided by strongly marked double lines.
In consequence of there being no distinct articulating surfaces,
the filaments are excessively fragile, so that it is rare
to find one of any length.
In the second subgenus, with which we have chiefly to do,
and the species composing which are, for the most part, inhabitants
of freshwater, the cells are truncate at their extremities,
so that their articulating surfaces are directly applied
to each other, and simply bilocular, and not globuliferous.
This subgenus admits also of further division, according as
the articulating surfaces of the cells are either plain or serrated,
and striated.
The genus Meloseira, amongst the Diatomaceoe, seems to
have been constituted with a view of making apparent the
affinity which undoubtedly exists between the Diatomaceoe
and the Algæ proper, not merely in form and developement
approximating so closely to the genus Vesiculifera amongst
the true Confervoe, hut also in a measure in its reproduction.
As in Vesiculifera, at a certain period, particular cells lose
their cylindrical form, and become globular or vesicular, and
contain endochrome : here, however, the analogy would appear
to cease ; for this endochrome, so far as my observation
goes, never becomes condensed into a distinct organ or sporangium
similar to that with which we are familiar in the
families Conjugateoe and Desmideæ. Notwithstanding this
striking resemblance to a genus of the Confervoe, the Melo-
seiræ ai’e true members of the family of Diatomaceoe, as is
clearly indicated by their silicious nature, and consequent
striated structure.
Derivation. From nfaipov, a globule, and ÿopjw, to bear.