490 ALISMACE^E. ( WATER- PLANTAIN FAMILY). 



flowered, in fruit continuous, oblong ; fruit thick-lenticular, obscurely 3-keeled; nutlet 

 slightly impressed on the sides; shell thick and hard; embryo nearly annular. 

 Cold ponds, White Mountains, New Hampshire, to Penn. June, July. 

 * * Stipules united with the sheathing base of the leaf. 



22. P. pectinatus, L. Stem filiform, repeatedly dichotomous ; leaves se- 

 taceous, attenuate to the apex, 1 -nerved with a few transverse veins; spikes inter- 

 rupted, on long filiform peduncles ; fruit obliquely broad-obovate, compressed, 

 bluntly keeled; shell of nutlet very thick; embryo nearly annular. Lake 

 Champlain to Lake Superior, and along the coast, both in fresh and salt water. 

 Aug. -Oct. (Eu.) 



23. P. Robbinsii, Oakes. Stem ascending from a creeping base, rigid, very 

 branching, invested by the bases of the leaves and stipules ; leaves crowded in two ranks, 

 recurved-tspreading, narrow-lanceolate or linear (3' -5' long and 2" -3" wide), 

 acuminate, ciliate-serrulate with translucent teeth, many-nerved ; stipules obtuse 

 when young, their nerves soon becoming bristles ; spikes numerous, loosely few- 

 flowered, on short peduncles. A single, rather immature fruit in Professor 

 Tuckerman's herbarium, from Prof. Eaton, is obliquely obovate, acutish at the 

 base, 3-keeled on the back, the middle keel winged, much arched on the thinner 

 face, compressed and impressed on the sides, and apiculate with the rather long 

 style ; superior portion of the large embryo circularly incurved and pointing 

 obliquely downwards. Oozy bottoms of ponds and slow streams : common in 

 New England : also in New York, Pennsylvania, and Ohio. Flowering in June 

 and July. Mature fruit not yet seen. 



(P. DENSUS, L. The plant upon which Schweinitz introduced this 

 European species into the U. S. flora proves to be Anacharis Canadensis.) 



ORDER 111. AL-ISMACE^E. (WATER-PLANTAIN FAMILY.) 



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

 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, 

 from 6 to many : anthers extrorse, 2-celled. Leaves sheathing at the base. 

 Comprises two very distinct suborders, viz. : 



SUBORDER I. JUWCAOINE^E. ARROW-GRASS FAMILY. 

 Calyx and corolla colored alike (greenish). Carpels more or less 

 united. Seed anatropous, with a straight embryo. Leaves petiole-like, 

 without a blade. (Flowers perfect.) 



1. Triglochin. Ovaries 3-6, united to the apex into one, but separating in fruit. 



2. Scheuchzeria. Ovaries 3, almost distinct, forming diverging pods in fruit. 



SUBORDER II. AL.ISMEJE. WATER-PLANTAIN FAMILY. 

 Calyx green and persistent. Corolla white, deciduous. Ovaries nu- 

 merous, distinct. Seed campylotropous : embryo bent double or hook- 



