ON SOME WATER PLANTS.
115
to the Primulaceae, it is an adventurous member of a family
of land plants which has taken to water-life. Its affinities are
easily recognized when the flower is examined. The whorls
of delicate lilac, yellow-throated flowers closely resemble some
of the Chinese Primulas, often grown in greenhouses, such as
P. malacoides ; but the leaves are unlike those of any Primula.
The blade on either side of the midrib is divided into stiff nar-
row segments with a pectinate arrangement. Adapted to
their surroundings the tissues enclose large air spaces, and on
the under surface of the leaf are many short glandular hairs,
which probably secret mucilage. Similar hairs are present on
the flower stalk. The succulent stems are fastened below to the
mud by slender white roots glistening from, the enclosed air
spaces. Throughout the year the circles of bright green leaves
may be seen under the water, often just beyond the collector's
reach; and this is not without its advantage when the plant
is in flower, for the sight of a bed of Water Violet in blossom
is apt to create in the heart of even the most philosophical botan-
ist a craving to possess at least one piece.
I have put these notes together to illustrate how rich our
neighbourhood is in Water plants, and in the endeavour to show
how much the interest in these plants is enhanced if their
structure is studied in relation to their surroundings.
In conclusion I wish to thank Mr. Dennis for the trouble he
has taken in making lantern slides from my drawings, and
also for the generous loan of his own beautiful slides showing
water plants growing in their natural haunts.
DESCRIPTION OF TEXT FIGURES.
Fig. 1.—Diagrammatic section of a pond with Water Plantain (Alisma
Plantago), showing seedlings in deeper water with ribbon-leaves only,
and in shallow water with aerial leaves; also a full-grown flowering
plant with submerged, floating and aerial leaves.
Fig. 2.—Arrowhead (Sagittaria sagittifolia). Plants in deep water with
ribbon-leaves only, and one in shallow water with leaves mostly
aerial and sagittate. Tubers occur on underground shoots.
Fig. 3.—Free end of a ribbon-leaf of Arrowhead, showing venation.
Fig. 4.—Small Bur-reed (Sparganium simplex), showing deep and shal-
low water plants connected by runners; the stream bed is seen in
section
Fig. 5.—Free end of ribbon-leaf of S. simplex, showing venation.
Fig. 6.—Great Sedge (Scirpus lacustris), showing plants in deep water
with ribbon-leaves only; in shallower water with ribbon-leaves and
flowerless scapes; and in very shallow water without ribbon-leaves
and with both flowerless and flowering scapes; river bed seen in sec-
tion.
Fig. 7.—Free end of ribbon-leaf of Great Sedge, showing venation.