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 



pond weed {Po- 

 Found in fresh, 



Fig. 14. — Fennel-leaved 

 tamogeton peetinatus). 

 brackish, or salt water. Cape Breton to 

 British Columbia, south to Florida, 

 Texas, and California. Also in Europe. 

 (After Britton & Brown.) 



Fig. 15. — Pickerelweed (Pontederia cor- 

 data). Borders of ponds and streams. 

 Nova Scotia to Minnesota, south to 

 Florida and Texas. (After Britton & 

 Brown.) 



Fig. 16. — Greater duckweed (Spirodela 

 polyrhiza). Found in rivers, ponds, 

 pools, and shallow lakes. Nova Scotia 

 to British Columbia, south to South 

 Carolina, Texas, northern Mexico, and 

 Nevada. Widely distributed in the old 

 world and tropical America. (After 

 Britton & Brown.) 



Fig. 17. — Lesser duckweed 

 (Lemna minor). Found in 

 ponds, lakes, and stagnant 

 waters throughout North 

 America below 58° N. lat. 

 Also in Europe. (After 

 Britton & Brown.) 



early growth. For fish-cultural purposes, however, their poor quali- 

 ties as food producers and oxygenators make them insignificant. 



