200 POPULAR FIELD BOTANY. 
TETRANDRIA. ‘TETRAGYNIA. 
PETALOIDE. NAIADACEA, 
POTAMOGETON. (PonpD-WEED.) 
Generic Character. Flowers divided into four parts, growing 
without stalks upon a spike, which issues from a sheathing leaf. 
Water plants. 
All the species of this genus grow in the water, and pre- 
sent a beautiful appearance, the leaves of some species being 
shiny, and floating on the surface. They are most useful in 
protecting the spawn of fish ; mollusca, innumerable insects, 
and aquatic birds feed on the seeds and roots. There are 
fifteen species described by botanists, but we must be con- 
tented with a few of the most common. 
Poramocrron pENsus. Opposite-leaved Pond-weed. Fre- 
quent in ditches; the leaves all opposite, without stalks, 
rather long and narrow, and growing below the water. 
Head of greenish flowers small and rounded. 
Poramocetron crispus. Cwurled Pond-weed. Leaves 
alternate on the stalk, long and narrow, waved and cut at 
the edges. Common in ditches and rivers ; the leaves under 
the surface. 
PoraMOGETON RUFESCENS. Reddish Pond-weed. This 
