14 
BULLETIN 465, U. S. DEPARTMENT OF AGRICULTURE. 
entire food of the bird. Thus it constitutes a slightly greater pro- 
portion of the subsistence of the bird than does wild celery. The 
importance of this plant was pointed out several years ago by Mr. 
H. L. Skavlem, of Janesville, Wis., who found that at Lake Kosh- 
konong its tubers formed from 60 to 80 per cent of the canvas-back's 
food. 
Besides the tubers on the roots, some pondweeds have winter buds 
among the leaves, and these, as well as the seeds, rootstocks, and 
indeed the whole plant, are eaten by ducks. As many as 350 tubers 
and no fewer than 560 seeds have been found in single stomachs. 
Pondweeds are realty staple food for ducks, and nothing is more 
common in the stomachs than the seeds of these plants. 
Fig. 8. — Propagating buds of wild celery. (Natural size.) 
The many species of pondweeds present a diversity of forms. 
Illustrations (figs. 9-17) of the nine species of general distribution 
serve to show the general appearance of some of these plants. All 
pondweeds are eaten by ducks, and any species would be a valuable 
acquisition for a ducking ground. 
The pondweed illustrated by figure 14 (P. perfollatus) is known 
as redhead or duck grass, and is an important duck food, said to be 
especially attractive to redheads. More has been found in the stom- 
achs of canvas-backs than of any other species. All told. 10 species 
of Potamogeton have been identified from duck stomachs, including 
all but one of the nine most widely ranging forms (figs. 9-17). 
