20 BULLETIN 465, U. S. DEPARTMENT OF AGRICULTURE. 
How to plant. — Pondweeds may be transplanted on a large scale 
by mowing 1 the whole plants with the seeds attached and scattering 
about where growth is desired. The seeds alone may be collected 
and sown broadcast, or they may be embedded in clay balls and dis- 
tributed over the bottom. 
Where to plant. — Most pondweeds require fresh water, but a few 
species, including the sago pondweed and its relatives listed on page 
17, will groAv in brackish or salt water. Mud bottom is preferable, 
but both sago pondweed and redhead grass will grow on sand. The 
water in which pondweeds are planted should be from 2 to 6 feet 
deep. 
When to plant, — The seeds may be planted immediately after gath- 
ering, or if cold storage is available they may be held until spring, 
as described in the case of wild rice. 
Seeds of the various species ripen at different times, but in the 
North they may be looked for after August. Those of sago pond- 
weed are in best condition in September and October. 
ENEMIES OF WILD RICE, WILD CELERY, AND PONDWEEDS. 
The three genera of plants thus far discussed — wild rice (Zizania) , 
wild celery (Vallisneria), and pondweeds (Po tamo get on) — vary 
greatly in abundance. The causes of this diversity are not well 
understood, but the plants have enemies whose habits are known and 
whose attacks may to some extent be warded off. Wild rice is gen- 
erally eaten by moose, deer, and cattle, but where the damage war- 
rants the necessary expenditure these animals can be fenced out. 
Muskrats tear up and eat these plants, but, so far as known, not to a 
serious extent. Carp also feed on them, and — 
the evidence seems to be pretty strong that in general they are very destructive, 
and are probably in large part at least responsible for the great destruction 
of wild celery and wild rice that has been noted in many of our inland marshes 
in the last few years. This, in turn, has deprived certain ducks, especially the 
canvas-back and redhead, of an important food supply, and has undoubtedly 
influenced their abundance to some extent in the localities in question. 2 
In waters controlled exclusively by one interest, carp may be ex- 
tirpated by partial or complete drainage and by the netting of the 
fish, together with the construction of wire screens or other barriers 
across all inlets and outlets. Where this is not practicable, sys- 
tematic poisoning with fish berries or copper sulphate may succeed, 
but only at the expense of many forms of life besides the carp, and 
in the long run it might be more injurious to the duck food than 
to the carp. However, these methods are applicable only in small 
1 A description of the machine for mowing aquatic plants may be found in the Report 
of the U. S. Fish Comm., 1892, pp. 477-478. 
2 Cole, Leon J.. Appendix Rept. Comm. Fisheries, for 1904, p. 592, 1905. 
