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IOWA ACADEMY OF SCIENCE Vol. XXV, 1918 



Poa pratensis. Kentucky Blue Grass. Figures 138 and 139. 



A dark green erect perennial. Resting' period same as Poa 

 compressa. Rhizome extensively creeping, averaging two mm. 

 in diameter, slender, having more conspicuous scales and nodes 

 than Poa compressa. New shoots are produced from the ends 

 of the rhizome only. Roots slender, fibrous, hairlike. Leaves 

 in new shoot forming distinct sheath, dark green, glabrous. 

 Blades two and one-half to four mm. wide, smooth, linear, com- 

 pressed at base, pointed at tip, flat. Sheath, smooth, compressed, 



Fig. 136. — Panicum virgatum. Switch Grass. A, ligule ; B, old culm; C, 

 old rhizome ; D, bud. 



white at base. Collar lig-ht green. Lignle narrow, entire, mem- 

 membranous, truncate; auricles wanting. 



Spartina cynosur aides. Slough Grass. Figure 140. 



A stout, erect perennial. Rhizome brown, very thick, creep- 

 ing, woody. Nodes at regular intervals, scales dark ; roots coarse, 

 having fine root hairs. GroA\'1:h of new shoot takes place from 

 base of old culm ; rhizome at this point is very thick w^here the 

 scales are somewhat twisted. Leaves rolled in the bud. Blades 



