428 Ittinois NaturAL History SURVEY BULLETIN 
other), areas substantiates) the = Grane 
Lake observations. Seed production 
of buttonbush is not known to vary 
greatly from year to year; therefore, we 
must conclude that ducks do not relish 
the seeds and that these seeds are sufh- 
ciently palatable to be taken extensive- 
ly only when other foods are lacking. 
Spike rushes, E/eocharis spp., include 
mainly the Eleocharis palustris group. 
These short, round-stemmed_ species, 
growing on moist soil or in shallow water 
may be excellent duck foods in some 
years and poor foods in others, as illus- 
trated by the index values in tables 4, 5 
and 6.. Tables 5: and 6 show that, in 
1939 and 1940, spike rushes formed 
about the same per cent of vegetation at 
the lakes studied. Yet in the first year 
the seed of these species consumed by 
ducks was three times as great as in the 
Fig. 12.—Water hemp (Acnida tuberculata) 
better known as pigweed, is generally a large, 
coarse moist-soil plant. It is of lower value as 
a source of duck food than are most other 
species growing on the I]linois River mud flats. 
Vol. 22, Art. § 
second year. We are at a loss#towame 
count for this variance. The 3-year in- 
dex rating for these species places their 
duck food value slightly below that of 
the longleaf pondweed, table 3. 
Water hemp, 4cnida tuberculata, fig. 
12, a large, coarse herb growing on drier 
soil sites than other moist-soil plants, 
has small seeds, pin-headed in shape, 
that may not always be as available as 
seeds of the other species of this group. 
Its index value for 1938-40 is 0.34, 
table 3. The data include seeds pro- 
duced prior to 1938, a year in which only 
a very few plants of this species grew in 
the areas studied. The 1940 rating of 
0.30 is probably the best indicator of its 
true value, table 6. Such moist-soil 
plants as smartweeds, millets and rice 
cut-grass are apparently about 10 to 40 
times as good sources of duck food as is 
water hemp. 
Marsh cord grass, Spartina Michaux- 
1ana, may be a fair duck food, as shown 
in table 3, with an index value of 0.24. 
This figure places it in a better position 
as a duck food in the I]linois River valley 
than it is customarily accorded else- 
where. 
Sago pondweed, Potamogeton pecti- 
natus, fig. 13, is generally regarded as one 
of the most excellent duck foods on the 
North American continent. However, 
it falls far short of this ideal in the Ihi- 
nois River valley. Tables 4, 5 and 6 
show that its 1938 index rating was 0.10, 
its 1939 rating was 0.06 and its 1940 
rating was 0.24. Table 3 shows a 3-year 
index value of 0.10. The low status of 
this highly rated species in the Illinois 
River region is due to its low seed yield 
here. Very little foliage and few tubers 
of this species were found in the 3,200 
gizzards analyzed. 
The apparently low seed yield of sago 
pondweed was substantiated by studies 
made in 1941 by Low & Bellrose (ms.), 
which revealed that this plant produced 
less seed per area unit than 23 other 
aquatic and moist-soil plants in the IIli- 
nois River valley. 
White waterlily, Castalia tuberosa, 
has an index figure of 0.10 for the 3-year 
period, table 3. However, its value 
may vary from year to year and place 
to place, depending on its own seed yield 
and on the presence or absence of other 
