ON SOME WATER PLANTS.
105
milky corm at the base of the stem, and thus a reserve of food
is prepared, from which new leaves are supplied the following
spring. The ribbon-leaves occur usually on seedlings only,
and do not often appear on second year's plants. On the other
hand, if the seeds are sown on mud at the edge of the pond,
no ribbon-leaves are formed, and aerial leaves with blades at
once are produced. Another interesting feature, illustrated by
the Water Plantain, which is shared by many water plants, is
that its geographical distribution is very wide. It occurs in
temperate parts of Europe, Asia and North America, that is all
round the northern hemisphere, and also in Australia. The more
constant and uniform conditions of water-life appear to account
chiefly for these plants having such a vast range.
Another species of Alisma, A. ranunculoides, used to grow
along the margins of our forest ponds, and perhaps does so still,
It is also heterophyllous, that is, it has leaves of various forms,
the first being usually submerged and grass-like, the later ones
aerial, with distinct but narrow blades. The corm, or solid
base of the stem, where food is stored, is not so stout as in the
Great Water Plantain and from it many long runners grow out,
which root and throw up fresh plants.
The third British species of Alisma is A. natans, the Float-
ing Water Plantain. It is described in our reference books as
being very rare in Britain and found sparsely in lakes in Wales,
in the north and West of England, in one locality in Scotland,
and in a few places in Ireland. Yet it grows in more than one
of our Forest ponds! How it was introduced there we do not
know, but it was probably by the agency of a botanist. How-
ever that may be, the delicate three-petalled white flowers
on slender stalks, rising just above the surface of the water,
surrounded by circles of glossy oval floating leaves, are charming
objects, and give one a thrill of pleasure as one realises how differ-
ent they are from the common, but no less beautiful Water-
Crowfoot flowers, which grow near them, and which in size and
general aspect they resemble. Both the long grass-like and the
floating leaves of Alisma natans may grow not only from the
base of the plant, but from the upper nodes of the slender flexuose
stem. In a dry season, when the water is low, plants may
be found growing in mud by the margin of a pond bearing only
oval short-stalked leaves which are entirely aerial.