ON SOME WATER PLANTS. 113
A case where the application of the theory seems more diffi-
cult may be seen in such a Monocotyledon as the Frogbit
(Hydrocharis Morsus-ranae) whose rounded floating leaves are a
conspicuous feature in summer on many of our ponds. In gen-
eral appearance they look much like small Water-lily leaves,
but the Water-lily is a Dicotyledon, and has true leaf-blades
with normal bundles only forming the veins, while the Frog-
bit leaves should probably be regarded not as leaf-blades, but
as expanded leaf-stalks; for they possess those significant in-
verted bundles, which seem to show us how the leaves are to
be interpreted.
This brief sketch gives but an inadequate idea of the matter;
to understand the evidence and full bearing of the subject,
I would refer those interested to Mrs. Arber's lucid paper in the
Annals of Botany.1
To return to the Frogbit. In the season of early spring
the only evidence of its presence in the ponds is to be found in
the smooth oval resting buds, which during the winter have been
lying in mud at the bottom, and now, quickened by the warmer
temperature, are rising to the surface, looking like little erect
acorns. Soon the sheathing outer scales fold back and the
first small upright leaves appear with minute kidney-shaped
blades (as for convenience they must still be called), and the
young rootless plants will be seen drifting about over the water
like little rosettes. In summer the larger floating leaves and
long hanging roots will have formed, and the frail white flowers
will appear; then long runners grow out, bearing at their ends
the resting buds by which the plant is chiefly propagated.
Water-lilies possess two kinds of leaves, namely, the familiar
substantial flat leaves that float on the surface of the water,
and also great wavy flaccid submerged leaves that never rise
to the surface. On the under side of both kinds are numerous
glands secreting mucilage, and this, by making the surface
slimy, probably prevents too rapid diffusion of substances
in the cell sap into the surrounding water.2 In some reference
books it is stated that Water-lilies also form long ribbon-leaves
when growing in deep water, but after vain search for them
I learn from a reliable authority that they appear to be entirely
1 Annals of Botany, vol. xxxii, No, cxxviii., Oct., 1918
2 See Willis "Flowering Plants and Ferns" ed,. 2. p. 162. H