104
THE ESSEX NATURALIST.
found in land plants; the water-conducting woody tissue is
much reduced; the temperature in Which the plants live is fairly
equable, encouraging free growth, which the abundant supply
of carbon dioxide dissolved in the water also favours. In order
to take advantage of all possible light filtering down through
the water, the epidermal cells often contain chlorophyll, which
is never the case with flowering plants on land; there are no
stomata, or none that are functional; to provide a supply of
air and ensure aeration a complete system of air chambers is
developed amongst the tissues. The leaves are buoyed up by
this means and brought nearer the light. In shape, these ribbon
FIG. I.
leaves are well adapted for life in slow streams; they bend with
the current, offering little resistance to it, and therefore are not
liable to be injured by the flow of water.
But the time comes when the needs of the Water Plantain
grow beyond that afforded by the ribbon-leaves; long-stalked
leaves are then produced with small oval blades, which often
float on the surface of the water. These floating leaves have
a similar structure to those of aerial leaves, except that their
stomata are all upon the upper surface. Later still, stronger
and completely aerial leaves are formed, with stiff stalks and
erect blades six to eight inches long; and finally the inflores-
cence is produced. Like most of our water plants the Water
Plantain is perennial. In autumn, starch is stored in the stout