16 BULLETIN 465, U. S. DEPARTMENT OF AGRICULTURE. 



Fig. 13. — Potamogeton prwlongus. 



Fig. 14. — Potamogeton perfoliatus. 



Fig. 15. — Potamogeton foliosus. B400M Fig. 16. — Potamogeton pusillus. 840IM 



Figs. 13-16. — Wide ranging species of pondweeds. (From Morong. ) 



