378 ALISMACE^. 



opening, 1 or 2-seeded. Seeds without albumen ; embryo 

 shaped Hke a horse-shoe. — Floating or swamp plants, with fas- 

 ciculate roots. Leaves with parallel veins. 



1. SAGITTARIA. Z/inw.— Arrowhead, 

 (From the Latin sagitta, an arrov) ; in allusion to th'e general form of the leaves.) 



Monoecious. Perianth 6 -leaved; 3 outer leaves persistent, 

 calycine ; 3 inner colored, petaloid. Sterile Fl. Stamens nu- 

 merous. Fertile Fl. Ovaries numerous, collected into a head. 

 Carpels compressed, 1-seeded, crowned with the persistent 

 style. 



1. S. sagittifolia Willd, : scape simple ; leaves sagittate or "sometimes 

 entire. 



var. 1. vulgaris Hook. : leaves ovate, acute ; the lobes ovate-lanceolate, 

 straight, acuminate, S. sagittifolia Mich. 



var. 2, latifolia Torr. : leaves very large and broad, more or less obtuse ; 

 the lobes ovate-lanceolate, spreading. S. latifolia Pursh. 



var. 3. haslata Torr. : leaves oblong-lanceolate, acute ; the lobes divari- 

 cate, lanceolate, elongated : flowers mostly dioecious. S*. hastata Pursh. 



var, 4, gracilis Torr. : leaves lance-Hnear ; the lobes much divaricate, 

 linear, very long and acute, sometimes wanting. S. gracilis and hetero- 

 phylla Pursh. 



var, 5. pubescens Torr. : leaves and stem pubescent ; bracts and outer 

 leaves of the perianth very pubescent. S", pubescens Pursh. 



var, 6. simplex Hook, : leaves with the lamina linear-lanceolate and with- 

 out lobes, S. simplex, graminea and ac^difolia Pursh. 



var. 7. rigida Torr. : leaves narrow-lanceolate, very acute at each end, 

 carinate beloW, /S". rigida Pursh. 



Ditches, ponds, and moist grounds. Can. to Flor. W. to the Platte River. 

 July, Aug. %. — Scape 6 inches to 2 feet high, ZiCaves very variable. Flowers 

 white. I follow Dr. Torre^ {N. Y. Fl.) in reducing all the above *forms to one 

 species. There seems to be more doubt concerning S. rigida, than any of the 

 rest. But they all pass into each other by almost imperceptible gradations. 

 Perhaps the following will hereafter also be found to be mere varieties of this 

 polymorphous plant. According to Nuttall it exudes a milky sap which hardens 

 into a white and hyaline gum. Common Arrowhead. 



2. (S. obiusa Willd. : leaves sagittate, dilated-ovate, rounded at the ex- 

 tremity, mucronate; lobes approximate, oblong, obliquely acuminate, 

 straight ; flowers dicecious ; sterile scape branched at base. 



Ditches and ponds. Penn. to Virg. July, '2J-. — Leaves about as large as those 

 of Calla paluslris. Flowers white. Obtuse-leaved Arrowhead. 



3. iS. p^Lsilla Nutt. : leaves linear, obtuse and short, the summits folia- 

 ceous ; scape simple, mostly shorter than the leaves ; flowers monoecious, 

 few, the fertile one usually solitary, Alisma suhdata Pursh. 



Muddy Banks. N. Y. to Geor, Aug. %. l—Scape 2 — 4 inches high. Leaves 

 rarely ever subulate, scarcely a line wide and obtuse. Flau^ers 3—6, only one 

 of them usually fertile. Dwarf Arrowhead. 



