16 BULLETIN 465, U. S. DEPARTMENT OF AGRICULTURE. 
Fig. 13. — Potamogeton prwlongus 
Fig. 14. — Potamogeton perfoliatus. 
Fig. 15. — Potamogeton 
Fig. 16. — Potamogeton pusilhis. 
Figs. 13—16. — Wide-ranging species of pondweeds. (From Morong. ) 
