tlie globules becoming entangled amongst their filaments
render them specifically lighter than the Avatcr, and cause
them to crepitate under the finger Avhen pressed upon. The
presence of these globides in warm weather causes the Con-
jugateoe and other Confervoe to present a vesicated or bullous
appearance, Avhlch the older algologists thought to he characteristic
of a single sjiecies, which they named Conferva
bullosa ; this appearance is now known to belong to a whole
host of Algæ generically distinct — such is the progress of
scientific research and knowledge. Dilhvyn, in his description
of Conferva fracta, observes, that, “ after being dried,
the Confervoe bullosæ have been used as wadding for stuffing
garments, and made into coarse household linen.” Weiss, in
his “ Plantæ Cryptogamiæ Floræ Gottingenses,” p. 23, relates,
that formerly the river U nstrut, after inundating a large trac t
of country in Upper Saxony, on again retiring into its proper
channel, left a great quantity of Conf bullosa, which having
been gathered and dried by the inhabitants, was used by them
for stuffing their garments ; but that it occasioned violent pains
in their limbs : it was also used for making coarse paper.” On
some parts of the Continent serious injury has been done
to large tracts of country, by the deposit, on the subsidence
of the waters which have covered them for a period, of a
compact layer of these Confervoe bullosæ, which has prevented
the growth of the grass beneath, and thus deprived
the cattle of their food. So great an evil has tliis been
deemed of late years, th a t commissioners have been appointed
to investigate the nature of this deposit, and to endeavour to
devise some means to remove and prevent its re-formation.
M. Deeaisne, in his “ Memoir on the Classification of the
Algæ,” has, on grounds ivhich, on mature consideration, I
cannot regard as satisfactory, separated this group from
Agardh’s class of zoospores, in which I would retain It ; for
certain it is that one division of the group of sunspores of
hi. Deeaisne, viz. the true Conferveoe, are propagated by
means of zoospores.
The numerous species of this group resolve themselves
naturally into the genera Zygnema, Tyndaridea, Staurocarpus,
Mesocarpus, and Mougeotia.
10. ZY G N FM A A ^ .
Char. Fndochrome arranged in spiral order within each cell.
Sporangia generally oval, and never lodged in the transverse
tubes o f communication.
Derivation. From ^oyo;, a yoke, and vrjpa, a thread.
Spirogyra Link, Handb. iii. 261., Meyen, in Linnaja, ii.
410. Choaspis Gray. Salinacis Bory, in Diet. Class.
XV. p. 75. c. iv. t. 45. Conjugatce sp. Vauch, Conf. d’F au
douce.
The first of these genera is characterized by the endochrome
with its brilliant granules (which Müller, in his surprise
on first discovering a species of the genus, likened to
precious stones), being arranged in a spiral form, the number
of spires being from one to eight.
The species of this genus admit readily of division into two
subgenera, in the one of which the filaments unite, and in
the other no conjugation takes p lace; and each of these divisions
allows of further analysis, founded on the conformation
of the cells.
“ In the first of these subdivisions, which for the most
part includes the long-celled species of the genus, such as
Zygnema elongatum and Z. quadratum, &c., the opposed extremities
of all those cells which have attained maturity are
considerably inverted, and which inversion may be compared
to tha t of the finger of a glove (PI. x v ii. fig, 4.) ; while in the
second, which embraces the short-celled examples, as Z y y -
nema maximum, Z . nitidum, and very many others, the cells
are not inverted, but touch each other by their plane surfaces.
“ The form of this inversion is, in all the species In which
it occurs, identical and extremely regular, its circumference
being circular, and its base somewhat flat; no membrane in tervenes
between the spaces formed by this indoubling in
contiguous cells, which spaces therefore communicate directly
with each other.
“ A t the period of reproduction, and at no other, one of
the two indented and opposed extremities of certain cells bc-
K 4
I B