98 THE FRESH-WATER AQUARIUM. 
the top of an arch, but not for the deep water of the tank. 
The plant is perennial and produces a white blossom, with 
one petal and four stamens. The flower-stem is velvety, 
and the leaves spread in a tuft from the root. 
POTAMOGETON DENSUS. 
Utricularia Vulgaris, or the hooded milfoil, may be re- 
commended as a botanical curiosity, but is met with only 
(as far I know) in the brooks of the southern counties— 
Hants and Surrey especially. It produces a yellow 
blossom in June and July. ‘The root has a curious in- 
flated appendage. ‘There are two other species, U. minor 
and U. intermedia, differing but little in general aspect 
from the common sort. 
