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PUBLIC HEALTH BULLETIN NO. 286 



18. Perigynium coriaceous with impressed nerves. 18. C hyalinolepis. 

 18. Perigynium membranous, the nerves or ribs 19. 

 not impressed. 

 19. Perigynium lanceolate, tapering into the beak, many 20. 



nerved. 

 19. Perigynium broader; abruptly contracted into the 21. 

 beak, usually strongly ribbed. 



20. Perigynium teeth reflexed, green 19. C. colUnsii. 



20. Perigynium teeth not reflexed, yellowish- 20. C. lonchocarpa. 

 green. 



21. Perigynium less than 1 cm. long 22. 



21 . Perigynium more than 1 cm. long 26. 



22. Perigynium body ovoid or globose, but not 23. 



truncately contracted into beak. 

 22. Perigynium body obovoid or obconic, trun- 20. 

 cately contracted into the prominent 

 beak. 



23. Perigynium coarsely ribbed or nerveless 24. 



23. Perigynium finely and closely ribbed 21. C. comosa. 



24. Pistillate scales rough-awned 22. C. lurida. 



24. Pistillate scales not rough-awned 25. 



25. Perigynium abruptly beaked, strongly inflated; pistil- 23. C. bullata. 



late spikes 20-40 flowered. 

 25. Perigynium less abruptly beaked, not strongly in- 24. C. elliottii. 

 flated; spikes 10-20 flowered 



26. Pistillate spikes globose or subglobose; style 27. 



straight; stolons short, ascending. 

 26. Pistillate spikes oblong or cylindric; style 28. 

 abruptly bent; stolons long, horizontal. 

 27. Perigynium rounded at base, shining; leaf-blades 2.5-8 25. C. intumescena. 

 mm. wide, their sheaths short prolonged upward at 

 mouth beyond base of leaf-blade. 

 27. Perigynium cuneate at base, dull, often hispidulous; 26. C. grayi. 

 leaf-blades 4.5-14 mm. wide; sheath not prolonged. 

 28. -Perigynium ascending; beak less than twice 29. 



length of body. 

 28. Perigynium spreading at right angles to spike 27. C. gigantea. 

 axis; beak 2-3 times length of body. 



29. Stems in tufts; leaf-blades 4-12 mm. wide 28. C. lupulina. 



29. Stems arising singly from elongate rootstock; leaf- 29. C. louisianica. 

 blades 2-5 mm. wide. 



30. Scales exceeding perigynia; achenes about 30. C. frankii. 



1.5 mm. long. 

 30. Scales much shorter than perigynia; achenes 31. 

 2.2-3 mm. long. 

 31. Beaks of perigynia appressed ascending; style straight 31. C. iyphina. 



below; achenes obovoid with concave sides. 

 31. Beaks of perigynia widely radiating; style strongly 32. C. squarrosa. 

 curved or bent below; achenes linear-oval with flat 

 sides. 



1. C. stricta Lam. — This tussock- forming species and its variety 

 strictior (Dewey) Carey occur only in the most northern part of our 



