Journal of Proceedings. lxvii
little of this be brought home and placed on a piece of moistened paper,
in a few hours a brilliant bluish green colour will be found to have
spread around the central patch. This is due to the fact that the simple
unbranched threads, each of which constitutes a plant, have the power of
moving in an oscillating manner, and have thus crept along the paper
free from the attached mud. From this peculiarity the plants of this
genus receive the name of Oscillaria. The group to which it belongs is
also characterised by the possession of a bluish colouring matter, and
are hence called Cyanophyceae This colouring matter exhibits a reddish
tinge when viewed by reflected light. Through the kindness of Mr.
H. C. Sorby, P.R.S., who has paid considerable attention to the
colouring matter of plants, I am able to lay a specimen of this sub-
stance before you. Two or three other genera, also belonging to the
Cyanophyceae, might also be looked for. Of these Lyngbya differs from the
above chiefly in the plants not having the power of locomotion. Spirulina,
differs from Oscillaria in the threads being twisted like a corkscrew. Beg-
giatoa is remarkable in this group for the absence of colour, for growing
on decaying Alga; where hydrogen sulphide is given off, and for the
presence of granules of sulplur in its fronds. No species of this genus
has been recorded as British, although B. lanugo is almost sure to be
found if carefully searched for, forming a white fringe on the fronds of
Ceramium rubrum. So far as is known the plants of these genera are
propagated only by the separation of the contents of the threads into
portions, each of which can, after leaving the parent frond, develop into a
new plant.
"Near high-water mark a number of green, grass-like Alga; are sure to
attract attention, either floating in the pool or attached to rocks or
stones. On gathering some of these it will be observed that some of the
threads are branched and others not so ; that some taper towards the
tips, while others taper towards the base. Those that are unbranched,
taper towards the base, and consist of a single series of cells, belong
to the genus Choetomorpha, i.e., bristle-shaped Algae; while those that
are branched, and whose threads consist of a single series of cells, belong
to Cladophora, i.e., branch-bearers. In both these genera the contents of
distinct cells become metamorphosed into two kinds of zoospores, i.e.,
living spores, so called because by means of cilia they are enabled to move
through the water, like Infusoria, from which indeed it is difficult some-
times to distinguish them except by their power of becoming attached
and germinating. The larger zoospores have generally four and the
smaller two cilia. These are believed to coalesce before germination.
The genus Enteromorpha often resembles Cladophora in habit, but under
the microscope the branches are seen to be composed of a number of
minute rounded cells irregularly arranged.
" The genus Ectocarpus resembles Cladophora in consisting of branched
threads, composed of a single series of cells, but differs in having a brown
colour, and in the character of the reproductive organs. These are of
two forms: the one globular, the simple cavity of which contains a
number of small zoospores ; the other more or less pod-shaped, divided
into a number of compartments, each of which contains a single large
zoospore. Both kinds of zoospores have only two cilia. The plants of
this genus are mostly parasitic on larger Alga;, and look like tufts of
brownish wool when in the water.
" The genus Mesogloia comprises a group of brown Algae that are easily
recognised by their gelatinous, slippery fronds of complex structure.
Most of the species not found as yet in England grow on the roots or
old leaves of Zostera.
"The species of the genus Callithamnion also resemble those of