e.

Some of the great group of _Algae_ attain enormous dimensions. Thus,
_Macrocystis_ (one of the _Melanospermae_), of the Southern Ocean, may be
even 700 feet in length. Another kind, _Lessonia_, forms submarine
forests, with stems like the trunks of trees.

The group of _Floridiae_ includes the delicate and elegant sea-weeds,
which are amongst the most admired vegetable productions of our coasts.
They are of interest, on account of various peculiarities in their
reproductive processes.

Other lowly plants may, at least provisionally, be placed in the great
group to which mushrooms and truffles belong--the group of _Fungi_--a
group the members of which agree in certain exceptional phenomena of
function,[20] as well as of structure and composition--as they are
exceptionally nitrogenous.

Amongst the lowest which we may for convenience provisionally include in
this group may be mentioned minute _Vibrios_, such as the _Bacteria_ so
much talked of in connexion with spontaneous generation, and the small
plant which by its growth produces fermentation--the yeast-plant
(_Saccharomyces_).[21] Closely allied to the yeast-plant are the
"moulds" which grow on organic matters such as _Penicillium_, _Mucor_,
_Saprolegna_, _Phytophthora_, the last of which is the potato disease.

A singular group of organisms goes by the name of _Myxomycetes_. These
enigmatical creatures have been classed in turn as animals and as
plants, and, indeed, at one period of their existence they seem to have
more resemblance to the former, while at another stage of their life
history they must unquestionably be ranked as plants. When young, they
are in a semi-fluid condition, and so move that they seem, as it were,
to flow over the body on which they rest. They grow upon the bark of
trees or on leaves and decayed wood. They exhibit movements like those
of the amaebae and are said to engulph nutritious matters which come in
their way.

The dry-looking, green, grey, red or yellow vegetable structures which
encrust our rocks, walls, and trees, and which are called _Lichens_,
form a group of plants curiously intermediate between Fungi and _Algae_.

Plants somewhat higher in the scale of vegetable life are those which
are termed liverworts (_Hepaticae_), including the scale-mosses
(_Jungermanniaceae_) and _Marchantia_. These plants, as we shall see, are
interesting on account of the variations to be found in the forms of
different genera. In many, ther