regular annulation of the enveloping membrane of the cells,
Avhich Avoulcl appear at a certain epoch to he intimately
adherent to the tissue of the cells themselves.
“ The genus of fresliAvatcr Confervoe which I have denominated
in a previous article Vesiculfera*, in addition to the
characters indicated in the definition of it given therein, such
as the attachment, attenuation and slight mucosity of the
filaments of the species composing it, as well as the formation
of true spores hy the intermingling and union of the contents
of two cells in the same filament, is particularly distinguished
by the presence of a peculiar and regular annulation of the
enveloping membrane of the cells, Avhich would appear at a
certain epoch to be intimately adherent to the tissue of
the cells themselves.” (PI. x v ii. figs. 7, 8.)
“ This annular disposition of the sheath of the cells does not
occupy Its whole extent, but corresponds only to certain cells
and determinate portions of those cells ; the cells around
Avhich it is disposed being those in which the spores are
destined to be formed, and the portion of these which it invests
being the extremities through which no endochrome
passes from the contiguous cells for the formation of the true
spores, or rather perhaps sporangia.
“ The number of annul! which correspond to each fructiferous
cell vai'ies according to the species, and Is more considerable
in the long-celled species ; it would appear however to
be never less than two, or more than eight or ten, to each cell.
“ The use of this interesting structure is much more apparent
than that of the provision already noticed as belonging to one
section of the genus Zygnema, and admits of a most satisfactory
explanation, it being manifestly designed to afford an
outlet to the Imprisoned spores, which it may be supposed to do
in the following way. As soon as the species has reached its
maturity and the spores have become perfected, the annuli,
which are intimately united to the cells, conti’act, most probably
from the arrest of growth and diminution of vitality
* This genus was first estabiishcd by me in tiie “ Annais and Magazine
of Naturai History,” voi. x. p. 385. ; it wiii be seen, iiowever, that
the views here expressed differ in many respects from those therein stated.
of the plant which occur towards the completion of the process
of reproduction, drawing along with them, and thus rupturing,
the slightly elastic membrane of the cells. (PI. x v ii.
fig. 7.) ^
“ Without some such beautiful and effectual provision, it
will bo evident, on reflection, that the spores would have to
remain immured within their narrow cells for an indefinite
length of time, even until, perhaps, their vitality had ceased
and the cells had become their coffins ; for occupying, as the
spores do, but a portion of the space of the cells, and enveloped
as they are in membranes, they can themselves, of
course, exert no influence in producing the rupture of the
walls of those cells.
“ In all the Confervoe with which I am acquainted, some
special m,eans are provided for the escape of the spores or
zoospores, their liberation never being left to the sole agency
of decomposition of the tissue of these plants ; thus, in the
majority of the branched Confervoe, and in the species of the
genus Sphoeroplea as well as in many other Confervoe, their
liberation is effected by the rupture of the cells in which
they are contained, which rupture is occasioned hy the devc-
lopement of the zoospores while still inclosed within the cells ;
in Conferva {Microspord) glomerata a special aperture exists
for the escape of the zoospores at the period of reproduction,
situated at one side of the distal extremity of each cell ; in
the Conjugating tribe the zoospores pass out through the
openings of the connecting tubes of the cells, which, when
reproduction has been completed, separate from each other;
and lastly, in the Vesiculiferoe, as has been shown, a more
complicated provision exists for the egress of the spores and
zoospores.
“ Of all characters whereby the Vesiculiferoe may be distinguished
from other Confervoe, th a t derived from the corrugation
of the investing sheath is perhaps the most valuable,
from the circumstance not merely of its being confined to the
species of that genus, but from its constant presence In all
stages of their developement ; and not only is it interesting as
being Indicative of a Vesiculifera, but also as pointing out
N 4