106 Cheney and True—Flora oj- Madison and Vicinity . 
Lemnace^e. (Duckweed Family. ) 
Spirodela, Schleiden. 
591. **$. polyrrhizci , Schleid. 
Abundant on all quiet waters of the region. 
Lemna, L. Duckweed. Duck’s-meat. 
592. L. trisulca , L. 
Growing with Spirodela polyrrhiza. Common. 
593. L. minor , L. 
With L. trisulca . Rarer. 
Wolefia, JBLorkel. 
594. W. Columbia;na, Karsten. 
Very abundant on the lakes in late summer and 
autumn. 
595. W. Braziliensis , Weddell. 
With W. Columbiana , much rarer. 
Alismaceje. (Water-plantain Family.) 
Alisma, Tj. Water-plantain. 
596. *A. Plcintago , L. 
Common in ditches, at margins of ponds, etc. 
Sagittaria, L. Arrow-head. 
597. S. variabilis , Engelm. 
Everywhere in shallow water. 
NAIADAGES. (PONDWEED FAMILY.) 
Triglochin, L. Arrow-grass. 
598. T. maritima , L. 
Growing in marshy grass land about lakes. Bare. 
Potamogeton, Tourn. Pondweed. 
599. P. natanSj L. 
Common in all the waters of the region. 
600. P. fluitans, Roth. 
University bay, Lake Mendota. 
601. P. amplifolius , Tuckerm. 
Growing in Lakes Wingra and Wabesa. 
