436 ALISMACE.E. (WATER-PLANTAIN FAMILY.) 



at the base (lj'-4 f long, the petiole 4' -12' long); stipules not winged nor 

 ridged; peduncle not thickened; fruit obtuse on the back when fresh. (P. louchites, 

 Tuckcrm.) P. oblongus, Viv., is a small-fruited form. Ponds and slow 

 streams; common. (Eu.) 



12. P. hctcropliyllllS, Schreber. Stem slender, branching ; immerse! 

 leaves lanceolate or linear and sessile, or only the upper pctiolcd ; floating leaves 

 elliptical, varying to oblong-linear, thinnish (l'-2' long), on filiform petioles; 

 united stipules 2-ribbed on the back; peduncle often thickened upivards; fruit aliyhtt.i/ 

 keeled when dry (one half smaller than in the preceding). (P. gramineus, L. 

 in part, Fries, *c. P. Claytonii, Tuckerm.) In shallow pools and ditches, as 

 well as streams ; common. (Eu.) 



P. CRfspus, L., I have not seen in this country. Mr. Tuckerman informs 

 me that he has seen a specimen in a European herbarium, purporting to have 

 been gathered in Delaware. If found, it may be distinguished from No. 8 by 

 its lanceolate and wavy-crisped 3-ncrved leaves. 



P. DENSUS was admitted into the first edition on the authority of Beck from 

 Schweinitz. I apprehend some mistake about it. The species, if in the coun- 

 try, may be known by its leaves being all opposite and without stipules. 



ORDER 116. ALISMACE^E. (WATER-PLANTAIN FAMILY.) 



Marsh herbs, with scape-like flowering stems, and perfect or monoecious 

 flowers, not on a spadix, furnished with both calyx and corolla : sepals and 

 petals each 3, distinct. Ovaries 3 -many, distinct or partly so, or if united 

 separating at maturity , forming as many 1- 2-seeded pods or achenia. Seed 

 ascending or erect. Embryo without albumen. Stamens hypogynous, 6 

 to many : anthers extrorse, 2-celled. Leaves sheathing at the base. Com- 

 prises two very distinct suborders, viz. : 



SUBORDER I. JUNCAGINE^E. THE ARROW-GRASS FAMILY. 



Calyx and corolla colored alike (greenish). Seed anatropous, with a 

 straight embryo. Leaves petiole-like, without a blade. 



1. TRIGLOCIIIN. Flowers perfect. Ovaries 3-6, united into one, but separating in fruit. 



2. SCHEUCIIZERTA. Flowers perfect. Ovaries 3, nearly distinct, forming diverging pods in 



fruit. 



SUBORDER II. ALISME^E. THE WATER-PLANTAIN FAMILY. 



Calyx green and persistent. Corolla white, deciduous. Seed campy- 

 lotropous : embryo bent double or hook-shaped. Loaves commonly fur- 

 nished with a blade. 



8. ALTSMA. Flowers perfect, with definite, mostly 6 stamens, fjirju'ls nmwnup, whorled. 



4 EOIIlX01>Oi;i:<. Flowers perfect,, with 7-21 stamens, i';,!-],!^ capitate, rilil.r.l 



{>. SAGITTAUT/V Klo\vcr< nnmurioiis. Stamens indefinite. Carpels capitate; winge 1. 



