IOWA ACADEMY OF SCIENCES. 
C. cristatella Britton. ( C . cristata) Schwein. 
Frequent in low woods. 
C. straminea Willd. Rare in woods. 
C. festucacea Willd. ( C. straminea brevior Dewey.) 
Common, and extremely variable. 
C. bicknellii Britton. (C. straminea var. crawei 
Boott.) Common on upland prairies. 
C. sychnocephala Carey. Rare in a marsh east of 
Armstrong; also at Spirit Lake. A plant very 
different in appearance from any other Ameri- 
can species of the genus. 
ARACEvE. 
Aris^ema Mart. 
15B. A. trip hy Hum (L.) Torr. Jack-in-the-pulpit; 
Indian Turnip. Frequent in rich woods. 
Acorus L. 
154. A. calamus L. Sweet-flag; calamus-root. Infrequent 
in marshes. 
LEMNACE^E. 
Spirodela Sclileid. 
155. S. polyrhiza (L. ) Schleid. (Lemna polyrhiza L.) 
Very common, floating on stagnant water, 
especially in bayous along streams. 
Lemna L. 
156. L . trisulca L. Ponds and marshes; frequent. 
COMMELINACEyE. 
Tradescantia L. 
157. T. virginiana L. Spiderwort. Open woods and 
prairies; common. 
PONTEDERIACEiE. 
Heteranthera R. & P. 
158. H. dubia (Jacq.) Mac M. ( Schollera graminea A. 
Gray.) Infrequent; shores of lakes. 
214 
148. 
149. 
150. 
151. 
152. 
