40 



Smith. R. B. 1917. A contribution to the life history of the 

 Pontederiaceae. Bot. Gaz. (Crawfordsville) 25: 324-337. 



Thieret, J. W. 1971. Observations on some aquatic plants in north- 

 western Minnesota. Michigan Bot. 10: 117-124. 



Wylie, R. B. 1917. Cleistogamy in Heteranthera dubia. Univ. Iowa Lab. 

 Nat. Hist. Bull. 7: 48-58. 



