THE CANVASS-BACK DUCK. 
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grows, on the roots of which they feed. This plant, which 
is said to he a species of valisineridj grows on fresh-water 
shoals of from seven to nine feet (but never where these 
are occasionally dry), in long, narrow, grass-like blades, of 
four or five feet in length ; the root is white, and has some 
resemblance to small celery. This grass is in many places 
so thick that a boat can with difficulty be rowed through it, 
it so impedes the oars. The shores are lined with large 
quantities of it, torn up by the Ducks, and drifted up by 
the winds, lying, like hay, in windrows. 
Wherever this plant grows in abundance, the Canvass- 
Baeks may be expected, either to pay occasional visits, or 
to make it their regular residence during the winter. It 
occurs in some parts of the Hudson ; in the Delaware, near 
Gloucester, a few miles below Philadelphia; and in most 
of the rivers that fall into the Chesapeake, to each of which 
particular places these Ducks resort; while, in waters 
unprovided with this nutritive plant, they are altogether 
unknown. 
On the first arrival of these birds in the Susquehanna, 
near Havre-de-Grace, they are generally lean ; but such is 
the abundance of their favourite food that, towards the 
beginning of November, they are in pretty good order. 
They are excellent divers, and swim with great speed and 
agility. They sometimes assemble in such multitudes as 
to cover several acres of the river, and when they rise sud- 
denly, produce a noise resembling thunder. They float 
