jugating species. I f two kinds of reproductive matter exist,
as most suppose, they must both be contained in the same filament
in these sjiecies ; but even this vicAv cannot be received
Avhen it is known that certain species of the family Conjugateoe
occur in Avhich there is not even a union of the matter of two
cells, but in which the sporangia are formed separately within
each ; as in Mesocarpus notahilis and Zygnema mirahile.
I t would thus appear tha t no argument can be deduced
from the conjunction of the cells in the same or different filaments
and the commingling of their contents in favour either
of the animality or sexuality of the Conjugateoe, and that the
phenomenon, remarkable as it is, is subservient to some secondary
purpose in the economy of these productions.
The species of this group of Confervoe may he found occasionally
In a state of conjugation during the entire of the
spring, summer, and autumnal months ; they are chiefly met
with, however, in this state in the spring. I t is usually some
days after this union of the cells has been established, that the
slow emanation of the matter of one cell occurs, this transference
being occasioned apparently by the mutual attraction
exercised by the contents of each cell on that of the one to
which it is joined ; this attraction, in correspondence with the
laAv of gravitation, being predominant in that cell which contains
the greatest bulk of matter ; and thus, I thinlc, we may
account for the contents of a number of cells of one filament
passing to those of another set of cells of another filament,
the matter in them being more considerable in quantity.
Very soon after the contents of the cells have united, they
are seen to dispose themselves into a regular form, and in the
course of three or four days the sporangia are perfected, each
being invested with its two or three membranes.
For some time, not unfrequently extending to weeks after
the cells have conjoined, and the sporangia have become organized,
the species does not appear to undergo any further
change : at length, however, the tubes of communication
separate, the cells become disjointed, indicating the death of
the plant, respiration ceases, and the disunited fragments fall
to the bottom of the water, the sporangia being set free on the
entire disorganization of the plant or the zoospores bursting
through the membrane which invests them, escape through
the open extremity of the communicating tubes.
When in a young condition, and before reproduction takes
place, the Conjugateoe are of a bright, beautiful, and shining
green colour, are highly lubricous to the touch, and the individual
filaments are never entangled together, hut placed
somewhat parallel. As soon, however, as a union of the
filaments has occurred, these characters are for the most part
lost. The rich green colour fades to a yellow tin t ; the filaments^
no longer glisten when removed from the Avater, or
feel slippery, but almost harsh and crisp under the fingers ;
they are noAv likewise much curled and twisted. The change
of colour is the result of diminished vitality, and the loss of
lubricity arises from the extension, amounting almost to obliteration
of the sheath.
The Conjugateoe, with a single exception, dAvell in waters
tha t are perfectly still, such as ponds, reservoirs, ditches,
pools, and extended marshes ; they are also, with a single
exception, unattached, roots not being necessary to them, for,
unlike the greater part of the Algæ Avliich have hitherto been
considered, and which are all provided with rootlike organs,
they incur no risk of being swept away by the force of the
river, stream, or cascade in which they 'delight to dwell.
The union between the filaments whieh is to occur, renders
a locality of the above description an essential to the very
existence of this famdy of plants, for without absolute
quietude of the water this conjugation Avould be frustrated.
In the only attached species with which I am acquainted,
and which dwells in flowing water, I have never detected
conjugation of the threads.
The Conjugateoe adhere strongly to paper, preserving their
shining appearance, but never their brilliant colours ; these
generally becoming almost black in drying.
The quantity of air or gas eliminated by the Confervoe,'
but principally by the Conjugateoe, in Avarm sunny weather
is very considerable. I t is by means of the globules of air
given out by these plants in respiration, that such large
masses as are seen in the spring and summer months, covering
almost every pond and ditch, are .sustained upon the surface,
K 3