Te See 
PLANT ASSOCIATIONS — ~~ aa 
as in the other species, the Water Milfoil. Both Hornwort 
and Milfoil have very much cut-up leaves—a feature common 
in water plants. Grass-wrack (Zostera) is an instance of an 
aquatic plant growing near the sandy edges of the sea, usually 
below low-water mark. The stem creeps and roots in the sand 
or mud, and it has long, grass-like, alternate leaves. Its flowers 
are adapted for pollination under water. 
Elodea and Water-soldier (Stratiotes) are instances of aquatic 
plants which are pollinated out of the water. Hlodea has 
already been described in some detail (p. 9). Water-soldier, 
like the Whorled Milfoil, has also a rootstock, creeping in the 
mud. This produces at the bottom of the water tufts of 
long narrow leaves bordered by small teeth. The ftlower- 
stalks rise a few inches above the water. This plant is common 
in the fens of eastern England. 
Frogbit (Hydrocharis) is a plant commonly found in canals. 
It has a floating stem, with floating tufts of radical leaves and 
_ submerged roots ; the leaves are about two inches across. The 
fruit ripens under water. It is thus partly submerged and partly 
out of the water; to this group belong also the Pondweeds 
_ (Potamogeton). These in many cases have two sets of leaves, 
some submerged, others floating on the surface. Duckweed 
(Lemna) is an aquatic plant, with stems floating on the surface, 
and generally called fronds, from the under surface of which 
are given off the roots (fibres) with distinct root-caps. This 
plant is found on the surface of ponds and still waters. 
Marsh and river plants are rather different in character 
from those just described. The characteristics of plants grow- 
ing by the banks of a river are that they are tall and narrow- 
leaved, whereas those which frequent marshes, and are beyond 
the reach of floods, often have large leaves, as, for instance, 
Docks, Butter-Bur, Wild Angelica. The plants by the banks 
of a river are chiefly Monocotyledons—e.g., Bur-reed, Sweet 
Flag, Bulrushes, Reeds, Cotton-grass, Sedges, Water-plantain ; 
where Dicotyledons occur they often have narrow lance- 
shaped leaves, as the Spearworts, p. 149. 
Some of the more common marsh plants are the Red and 
