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PUBLIC HEALTH BULLETIN NO. 2 86 



20. All leaves long and narrow 21. 



20. Upper leaves shorter and broader (fig. 17) Callitriche, p. 121. 



Figure 16. 



Figure 17. 



21. Plants lax, not rooting along the stem 22. 



21. Plants stiflF, rooting along the stem; leaves 



stiff and often in fascicles (fig. 18). Juncus, p. 107. 



22. Leaves with dilated bases (fig. 19) Najas, p. 71. 



22. Leaves with narrow bases (fig. 20) Zannichellia, p. 71. 



Figure 18. 



Figure 19. 



Figure 20. 



