108
THE ESSEX NATURALIST.
is fairly common, only stiff aerial leaves are formed. Plants
living in deep running water produce only ribbon leaves, which
may be from two to four feet long. When growing with those
of Arrow-head, they can be easily confused with them, but the
Bur-reed leaves have a weak midrib, and are traversed by
from eleven to thirteen parallel veins, enclosing short rectangu-
lar air chambers. Many runners grow out from the base of the
stem; some lie along the bottom of the pond or stream, and are
green, others, buried in mud, are White. They are stored with
starch, and are provided with an abundant system of air chambers
which are in communication with the air-space in the leaves.
No conspicuous perianth is ever developed in the Reed-mace
FIG. 4.
family, to which Sparganium belongs, but the round yellow heads
of stamens and the pale balls of pistils are showy objects in
summer amongst the shining bright green leaves.
The larger Bur-reed, Sparganium erectum L. (or S. ramosum
Huds.) grows by the lake in Wanstead Park, in the Roding, and
in some of the larger forest ponds. It is stouter in all parts
than S. simplex and the leaves are strongly keeled nearly to
the tip. Submerged ribbon-leaves seem to be very rarely
formed.
These two species, as well as the graceful Sparganium natans
L., whose leaves are all either submerged or floating, and which
has not, I think, been recorded for Essex, are very widely