16 AQUATIC PLANTS IN POND CULTURE. 
The two duckweeds, Spirodela polyrhiza and the more common 
Lemna minor, are not highly esteemed, though not especially objec- 
tionable. The larger form is quite ornamental, and both are of 
Fic. 14.—TFennel-leaved pondweed (Po- 
tamogeton pectinatus). Found in fresh, Fic. 15.—Pickerelweed (Pontederia cor- 
brackish, or salt water, Cape Breton to data). Borders of ponds and streams, 
British Columbia, south to Florida, Nova Scotia to Minnesota, south to 
Texas, and California. Also in Europe. Florida and Texas. (After Britton & 
(After Britton & Brown.) Brown.) 
Fic. 16.—Greater duckweed (Spirodela Fic. 17.—Lesser duckweed 
polyrhiza). Found in rivers, ponds, (Lemna minor). Found in 
pools, and shallow lakes, Nova Scotia ponds, lakes, and stagnant 
to British Columbia, south to South waters throughout North 
Carolina, Texas, northern Mexico, and America below 58° N. lat. 
Nevada. Widely distributed in the old Also in JHurope. (After 
world and tropical America. (After Britton & Brown.) 
Britton & Brown.) 
early growth. For fish-cultural purposes, however, their poor quali- 
ties as food producers and oxygenators make them insignificant. 
