FIVE IMPORTANT WILD-DUCK FOODS. 15 
nearly half of the entire food of the 10 vegetarian species of ducks 
occurring there at the time. This showing is much more significant 
from the fact that sago pond weed (Potamogeton pectinatus) also was 
abundant in the lake. The latter plant, in the writer's opinion, is the 
best all-round duck food * in North America, yet at Lake Surprise it 
furnished somewhat less than 29 per cent of the food of the ducks in 
comparison with more than 48 per cent supplied b} 7- NympJisea 
mexicana. 
Thirty-seven canvasbacks collected at Lake Surprise had eaten 
various parts of this plant to the extent of 71.6 per cent of their diet. 
This is a second illustration of the unusual phenomenon of the canvas- 
back's being attracted to shallow water by a highly prized food. 
Six ring-necked ducks or blackjacks made more than 91 per cent of 
their food of this plant, and two southern black ducks {Anas ful- 
vigula) 98 per cent. The parts eaten are the rootstocks, stolons, 
tubers, and seeds. Mr. Charles W. Ward has sent us rootstocks 
of NympJisea mexicana from Avery Island, La., with the information 
that this' plant and wild celery ( Vallisneria spiralis) furnish the bulk 
of the food of canvasbacks in that locality. 
DESCRIPTION OF PLANT. 
For the purposes of field identification the water lilies of the United 
States may be divided primarily into two groups according to 
the shape of the leaf. Two genera, the water shield (Brasenia) 2 
and the American lotus, or water chinkapin (Nelumbo) , 2 have entire 
circular leaves with the leaf stalks attached at their centers. The 
remaining two genera have more or less heart-shaped leaves or a 
circular or oval leaf with a cleft or sinus from the edge to the point of 
attachment of the leaf stalk. Of these two genera, one (Nuphar), 2 
including the spatterdocks or toad lilies, has the top or more of the 
ovary plainly visible when in flower, the other has the ovary practi- 
cally hidden by the very numerous stamens. To this last group 
belongs Nymphsea mexicana, and it is the only native species of the 
genus that has yellow flowers. 
Both the leaves and flowers of this species may either float on the 
surface of the water or stand a few inches above it. The leaves are 
green above with brown mottlings and vary from greenish to purplish 
red below with small black markings. The edges of the cleft of the 
leaf are either somewhat separated or overlapping (fig. 13). The 
plant springs from an upright rootstock (fig. 14) which bears some 
resemblance to an unopened pine cone. The rootstocks vary in size 
up to 2 inches in thickness and 12 inches in length. The smaller ones 
(at least up to If inches in length by three-fourths of an inch in 
thickness) are swallowed by ducks. 
1 See Biological Survey Circular 81, pp. 11-17, for full account. 
2 The seeds, at least, of all these plants are eaten by many kinds of ducks. 
