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of them ; so that if we examine any species in which this law
is knoAvn to exist, we shall observe, first, th a t the filaments
differ considerably in diameter in the same specimens ; secondly,
if the species be a branched one, that the largest
filaments are near the centre of the specimen ; and, thirdly,
that the diameter of all the filaments, whether they be near
the centre or circumference, gradually decreases from base
to apex ; the observation of these three facts proving the
existence of the law of the lateral developement of cells,
and also showing it to be in the degree of their age. The
proportions of a specimen of a branched Conferva, therefore,
are in miniature those of a tree or shrub. This law has no
existence in the conjugating Conferva in the genera Bulbo-
chate and Desmidium, and in the majority of Oscillatoria. One
or tAvo other observations still remain to be made in reference
to cells, to complete the interesting subject of the
developement of the Conferva. Prior to the discovery of the
multiplication of cells by division, the opinion Avas generally
entertained tha t each cell Avas at Its commencement very
small, and that it increased little by little, until it attained
its perfect developement ; and this is the case with the cells
of parenchymatons tissue; but in the examples Avhere the
multiplication of cells takes place by division of those cells
which have already become great, nature takes a means for
the fulfilment of its end, altogether different, but not less
effectual.
I t has already been mentioned that the different series of
cells of Avhich the Conferva are composed, are all enveloped
in a continuous membrane, which serves to bind them together;
there would appear, however, according to the re-
searclies of Agardh and Hugo Mohl, to be another and direct
bond of union betAveen the cells, not merely of the Algæ,
but of all other plants, this consisting in an adhesive substance
Avhlch Mohl has denominated “ intercellular,” by which
they are firmly united to each other. The same substance is
found coating the surfaces of the pollen granules, binding
them into masses.
Having thus traced the developement of the Conferva from
their earliest period, viz. from the condition of zoospoi'es, and
having examined their structure and modes of groAvth, we
shall next proceed to make a feAv remarks upon their distribution
and vitality.*
Not amongst the least beautiful of the many minute oi’-
ganizations, whose intimate structure the microscope, which
has so wonderfully extended of late our knoAvledge of the
natural Avorld, has revealed to us, are the freshwater Alga,
and yet the majority of these constitute the rejected and
despised, by all hut the true naturalist, scum and slime of our
still and soft Avaters; but although many freshwater Alga
are, for an obvious and benevolent purpose, hereafter to be
mentioned, ordained by their Great Designer to be the tenants
of our impure and stagnant waters, there are other species
which are met with only in fresh and running streams, adhering
by one extremity to some object of attachment, the
other floating freely in the surrounding fluid medium in the
course of the stream, whose impetuosity and strength these
frail productions seem at first sight but ill able to withstand.
They find their protection, however, not less in the flexibility
than in the tenacity of their structure. This is the case
with the Lemania, Lyngbya crispa, and with the beautiful
Conferva glomerata, which delight in the purest and most rapid
streams. The Ectosperma clavata of Vaucher, known by its
globular form and dark green shining appearance. Is met
with only in the course of the waterfall or cataract, sustaining
unharmed the whole force and weight of the foaming
waters which pour over it. The Batrachosperms, the most
elegant of all our freshwater Conferva, also usually dwell
In pure water, but are obliged, for the most part, from the
delicacy of their conformation, to confine themselves to such
streams and rivulets as are slow, and possess but little
strength; while some Conferva, as many species of Zygnemata,
Tyndaridea and Mougeotia, are almost exclusively
confined to marshes, ditches, or shallow and extended pools,
* For a highly interesting memoir upon the connection of the cells of
plants, by Hugo Mohl, see Annales des Sciences Naturelles, second series,
tom. viii. (Botanique).
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