44 PUBLIC HEALTH BULLETIN NO. 2 86 



24. Stem usually triangular in cross-section Cyperaceae, p. 84. 

 particularly near base (edges sometimes 

 rounded) ; leaves 3-ranked, flowers in close 

 clusters and concealed by overlapping 

 scales. 

 24. Stems round in cross-section, leaves not 3- 25. 

 ranked. 

 25. Leaf with a ligule at base (junction of leaf and sheath) Graminae, p. 76. 

 (fig. 19). 



25. Leaf without ligule 26, 



26. Leaves with sheaths at base 27. 



26. Leaves without definite sheaths, but bases 29. 

 sometimes sheathing. 



27. Leaves narrow, mostly less than 1 cm. (fig. 20) Juncus, p. 107. 



27. Leaves broader 28. 



Figure 19. 



Figure 20. 



28. Sheaths abruptly contracted to blade of leaf ; Typha, p. 68. 



leaves without keels (fig. 21). 

 28. Sheaths narrowed to blade; leaves with keels Sparganium, p. 68. 



(fig. 22). 



x'/6 



x'/3 



U ^'/e 



Figure 21. 



Figure 22. 



