436 ALISMACE2E. (WATER-PLANTAIN FAMILY.) 



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

 ridaed; peduncle not thickened; fruit obtuse on the back when fresh. (P. lonchltes, 

 Tuckerm.) P. oblongus, Fiu., is a small-fruited form. Ponds and slow 

 streams; common. (Eu.) 



12. P. heteropliyllus, Schreber. Stem slender, branching ; immersed 

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

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

 united stipules 2-ribbed on the back ; peduncle often thickened upwards ; fruit slightly 

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

 in part, Fries, frc. P. Claytonii, Tuckerm.') In shallow pools and ditches, as 

 well as streams ; common. (Eu.) 



P. CESSPITS, 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-nerved 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. AL-ISMACE^. (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. JUNCAGINEJE. THE ARROW-GRASS FAMILY. 



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

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



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



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



fruit. 



SUBORDER II. ALISME2E. THE WATER-PLANTAIN FAMILY. 



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

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

 nished with a blade. 



8. ALISMA. Flowers perfect, with definite, mostly 6 stamens. Carpels numerous, whorled 



4. ECHINODORDS. Flowers perfect, with 7-21 stamens. Carpels capitate, ribbed. 



5. SAGITTARIA. Flowers monoecious. Stamens indefinite. Carpels capitate, winged. 



