i i ’
pieces, and yet each separated portion will retain its vitality
unimpaired, and go on increasing as before ; but this is
owing, in a measure, also to the fact of each cell in the
series enjoying an independent vitality. They also sustain,
unharmed, considerable vicissitudes of weather, notwithstanding
which they are, however, regular barometers, rising and
sinking in the fluid medium which surrounds them alternately,
either as the sun shines, and Avarmth is diffused, or as
clouds and rain obscure the sky, and cold prevails. In this
Avay, too, they protect themselves in a great measure from
the alternations of weather, the water being much Avarmer
beneath the surface than on it. This poAver Avhich the
Conferva possess of rising and sinking in water, in correspondence
Avith atmospheric changes, is to be explained by
reference to their specific gravity, Avhich is in proportion to
the activity Avith Avhlch the function of respiration is carried
on. During the autumnal and early spring months, the
Conferva remain almost entirely at the bottom of the water,
except Avhen tempted by a fcAV sunny days to rise to the
surface, and expose themselves to the contact of the air, so
that the naturalist engaged in the investigation of these
productions is often surprised on visiting ponds in which he
beheld the day prcA’iously Conferva floating on the surface
in considerable quantity, to find that on his next visit they
have all A’anished. The Cotferva are also amongst the first,
if not the very first, subjects of creation to feel the approach
of more genial Aveather, beginning to vegetate sometimes so
early as the months of January or February.
In the preceding pages it has been assumed that the fresh-
Avater A lga are really Avhat many observers have been
inclined to doubt, viz. vegetable productions or plants, they
being led so to do, first, from the curious and extraordinary
motions of the zoospores already described, and second, from
the peculiar and animal fcetor which the different species
exhale during decomposition. Their true position in the
scale of . organized beings has been, it seems to me, satisfactorily
determined, not merely by reference to certain resemblances
Avhich they bear to vegetables in appearance and
organization, but also and mainly by chemical analysis. In
the 14th volume of the second series of the “ Annales des
Sciences Naturelles (Botanique, 1840)” is an elaborate and
highly interesting memoir by M. Peyen, on the chemical
composition of vegetable tissue. In this memoir, M. Peyen
establishes a distinction between animals and vegetables
based upon the chemical difference which he has ascertained
to exist between the cellular membranes of the respective
divisions of the organic world. The vegetable tissue, M.
Peyen finds, to exhibit invariably a t e r n a r y composition,
that Is, it is composed of three out of the four elementary
constituents of Avhich all bodies are formed, viz. carbon,
hydrogen, and oxygen in nearly fixed proportions, as folioavs : ■—
carbon 44, hydrogen 6, oxygen 50. The composition of the
animal tissue or membrane, on the contrary, is as invariably
QUATERNARY, Or formed of all the elementary constituents in
less fixed proportions. This generalization is arrived at by
an extensive and careful analysis, not only of animal substances,
but also of examples of most of the families and
orders of Phanerogamic and Cryptogamie plants. Amongst
the freshAvater Alga an analysis Avas made of Conf rivularis,
Oscillatoria, and Chara, these all offering the same result as
the other analyses of vegetable tissue, and therefore being conclusive
as to the vegetable character of the Confervoid division
of the Alga. I t is to be regretted tha t an analysis was not
made of the Desmidea and Diatornea, with a view to determine
more certainly than has yet been done their position
in the scale of beings. That the Desmidea are really vegetable
productions, scarcely a doubt remains, iodine demonstrating
the presence of starch in abundance in the contents
of their cells.
The following are the steps adopted by M. Peyen in order
to free the membrane of the Conferva rivularis and Oscillatoria
from all extraneous matter, and thus to prepare it for
analysis : —
“ I tried next to test, with the same object in view, very
many Conferva. Soda, by dissolving with heat the investing
membrane of the filaments of Conferva rivularis, separated
D 4
M!