24:2 



flowers alternate. Staminate petals four, longer than the stamens, 

 oblong, pale, rose-colored, deciduous. Stamens eight. Fruit 

 looking like a square block, ij4 mm. long and broad. Carpels 

 turgid, rounded on the back with a deep intervening groove. A 

 deep water plant. 



Greenland, Lake Termiscouata (Northrop), and Lake Mem- 

 phremagog, Canada, near the United States boundary (Churchill). 

 Common in Europe. 



3. M. verticil latum. L. Sp. PI. 992 (1753). 



Submerged leaves in crowded verticils of threes and fours, i to 

 4 cm. long, the capillary divisions ten to twelve pairs, often min- 

 utely scabrate. Floral leaves pectinate- pinnatifid, or pectinate, 

 much longer than the flowers. Petals four, purplish in color on 

 the sterile flowers. Stamens eis^ht. Fruit 2 to 3 mm. long, and 

 2^ mm. broad, somewhat gibbous at the base. 



In deep and shallow water. Ontario (Macoun's Cat). Same 

 range in United States as No. 2. Common in Europe. 



4. M. tenellum. Big. Fl. Bost. 346 (1824). 



Stems slender, scape-Hke, nearly leafless, simple, erect, 4 to 

 35 cm. high, nearly all out of the water, from a long rhizome, 

 which sends up many sterile shoots. Flowers alternate, solitary 

 subtended by small, entire bracts, the uppermost obovate and often 

 longer than the flowers, the lower oblong and generally shorter 

 than the flowers, the lowest part of the spike often bractless. 

 Stem with scattered bracts or often naked. Staminate petals four, 

 longer than the stamens, somewhat persistent, purphsh in color. 

 Stamens four. Fruit I mm. long and i mm. broad at the apex, 

 spreading to i^ mm. at the base. Carpels rounded or obtusely 

 angled on the back, the groove shallow. 



Frequent in Canada, New England, New York, Pennsylvania, 

 and west to Michigan. 



5. M. Iiumile. (Raf). 



Piirshia humilis. Raf Med. Rep. 2nd. Hex. 3,422 (1806). 



M. ambigiium var. Hmosum., Nutt. Gen. 2, 212 (1818). Torr. 

 Comp. 355 (1826). Gr. Man. Ed. i, 140 (1848). 



This plant occurs in several forms according to the situation in 

 which it grows. These forms, when seen only in dried herbari- 

 um specimens, might be easily mistaken for distinct species, so 



