this mode of growth likewise takes place in all other Confe
r v a consisting of a single series of cells, are little less conclusive
than those ju st enumerated. In most of the filaments
of these, the cells will be observed to be of various lengths,
some twice as long as others, and others again of every intermediate
length. Now, by means of this laAV of growth, the
variation in the length of the cells is at once and satisfactorily
accounted for, which is not to be done in any other way.
B u t this is not all ; the progress of the formation of the
septa which divide the cells may he frequently traced,
a contraction of the cuticle and a division of the endochrome
gradually occurring, which is alone sufficient to establish the
reality of this laAV of increase or multiplication of cells in all
the true Conferva, and which may be stated to extend
likewise to all the other A lg a— the Ulvacea, Desmidea, and
Diatomacea. In those Desmidea however which are not
filamentous, but which are formed of two symmetrical cells,
the multiplication by growth is often very different. On the
separation of the cells from each other, each will throw out a*
mass of viscid mucous matter, Avhich will go on increasing
until it finally takes on all the characters of the primitive
cell. Now, particular stress should be laid on this law -of
developement, since it is evidently very important, inasmucli
as it not merely so satisfactorily and so beautifully accounts
for the rapid growth of all articulated Alga-—for It is simultaneously
in operation in each of the many hundred cells of which
each filament is usually composed — but it teaches us likewise
that much caution is requisite in employing the character
of the length of the cells for determining species, as it proves
that this character, which used formerly to be much relied
on for the purpose, is one subject to very great variation.
There is a limit, however, to this law of developement which
does not in the genus Zygnema allow of more than one or
two divisions of each cell, unless indeed the spiral tubes grow
likewise in an equal ratio, which may be the case, and then the
division of the cells may be frequently repeated. In those
Conferva Avhich do not contain spiral tubes the multiplication
of the cells may go on to an almost endless extent.
Since the above observations were Avrltton *, my attention
has been directed hy Mr. Francis to a lecture hy M. Morren,
inserted in the “ Bulletin de I’Acadcmie Boyal des Sciences
de Bruxelles,” for 1837, from the perusal of which it
appears that the growth of many Conferva by the division of
the cells has been noticed by more than one observer. From
this lecture I make the folloAving ex tra cts: —
“ In 1832, M. Dumortier published his memoir upon the
structure and developement of plants and vegetables, in Avhich
he established with the greatest clearness the fact of the
increase of a number of cells hy division. His researches
Avere carried on upon Conferva aurea, in Avhich the terminal
cell elongates itself more than the others, in order to form in
its interior an intermediate production (partition), which
divides the cells into tAVO parts, each becoming a new cell.”
No one could be more explicit, observes M. Morren, who
goes on to say, “ the division of cells by intermediate membranes
Avas examined likewise by M. Hugo Mohl in September
1835, upon Conferva glomerata, &c., a terminal cell of which
shoAved near its centre the commencement of a diaphragm
proceeding from the circumference toAvards the centre.” This
is in all respects, M. Morren remarks in continuation, the
observation of M. Dumortier, but upon another species, and
it is all simply the fact previously noticed by myself upon
Cruciagenia, but transported from the Diatomacea to the
Conferva.
From this it appears that M. Morren Avould claim for
himself priority in the discovery of the increase of cells of
Cotferva by division, but the single observation published
in August 1830, upon the genus Cruciagenia, an Alga
differing much in structure from true Confervoid productions,
would hardly suffice to establish for M. MoiTcn this claim
any more than Avould the observation of Mirbel on the
division of the pollen cells give him a claim to the discovery
* The substance of the preceding remarks, on the growth of the Algts,
is extracted from a portion of an “ Essay on the ConfervEe,” read before
the Dublin Natural History Society and inserted in the “ Annals and
Magazine of Natur.al History,” vol. i. p. 431.