14 BULLETIN 936, U. S. DEPARTMENT OP AGRICULTURE. 
{Salix exigua). and black willow (Salix amygdoloides). (PI. III. 
fig. 2. and PI. IV.) 
It is thus evident that the conditions found in the Bear Piver 
marshes leave little to be desired in the way of duck-food plants. In 
other regions improvement frequently may be brought about by in- 
troducing suitable plants for cover and for additional food supply. 
These marshes are so favored that artificial introduction of plants 
would not seem to be needed. 
Among plants not found there, but considered valuable duck foods 
and possible of introduction, is wild celery (VaUisneria spiralis) , as 
this plant can grow in brackish water. Whether such introduction 
would be successful can be ascertained only by experiment. This 
plant grows submerged and to thrive would require the deeper situa- 
tions, as in certain channels in the upper sloughs, or in the Chesa- 
peake Bay. Wild rice {Zizania palustris), the only other plant of 
importance that might be considered, can not endure salt to any ex- 
tent, so that the alkaline waters and soils of Bear Piver would pre- 
clude its successful introduction, except possibly in certain small, 
restricted areas. In the long run. without much doubt, it will be 
found that the present marsh vegetation is best suited to these exten- 
sive flats. Soil conditions, as regards alkalinity, change and shift 
annually with changes in the water level of the lake itself, and with 
the volume of stream flow in Bear Piver. The marsh vegetation ad- 
vances and retreats year by year, adjusting itself according to certain 
limits of tolerance for alkalis, in one place extending its bounds and 
in another being killed out and forced to withdraw. At present the 
tendency is for the tule growth in the lower part of the marsh to be 
driven back, while extensive flats above the true marshes, that in 1914 
were open alkaline barrens, in 1915 and 1916 were covered with a 
luxuriant growth of salt grass. Masses of submerged tule roots to 
be found downstream several miles below the present living growth 
attest the former limits of the marsh vegetation. Holes dug to a 
depth of 2 or 3 feet at various places on the marsh often showed a 
narrow layer of black soil containing remains of Scirpus stems and 
root bulbs beneath a layer of barren clay 18 or 20 inches thick, indi- 
cating an ancient marsh area, long ago entirely killed out and sub- 
merged. It is doubtful whether introduced plants from regions 
where the struggle for existence is less keen would be able to adapt 
themselves to such frequent shifts and changes in environment. 
ANIMAL FOODS. 
Though most of the ducks found on the Bear Piver marshes draw 
their staple food supply from seeds, tubers, or other vegetable mat- 
ter, there are certain animal foods in this area that are of sufficient 
