FKOG'S-BIT FAMILY. 321 



always tapering into the thick petiole, the nerves nearly all from the thick 

 and prominent midrib. 



S. variabilis. The common species everywhere, exceedingly variable; i;: 

 almost all the well-developed leaves arrow-shaped; filaments nearly twice the *" 



length of the anthers, smooth ; akenes broadly o'lovate, with a long and 

 curved beak ; calyx remaining open. 



S. calyeina. Along rivers, often much immersed ; many of the leaves 

 linear or with no blades ; the others mostly halberd-shaped ; scapes weak, 

 3' -9' high ; pedicels with fruit recurved ; filaments roughish, only as long as 

 the anthers ; akenes obovate, tipped with short horizontal style ; calyx appressed 

 to head of fruit and partly covering it ; the fertile flowers show 9-12 stamens, 

 the sterile occasionally some rudiments of pistils. 



* * Filaments very short and broad. 



S. heteroph^lla. Common S. & W. : scapes 3' -2 high, weak; the 

 fertile flowers almost sessile, the sterile long-pedieellcd ; filaments glandular- 

 pubescent ; akenes narrow-obovate, with a long ei-ect beak ; leaves linear, lance- 

 olate, or lance-oblong, arrow-shaped with narrow lobes or entire. 



S. graminea. Common S. : known from the foregoing by the slender 

 pedicels of both kinds of flowers, small almost beakless akenes, and leaves 

 rarely arrow-shaped. 



S. pusilla. From N. Jersey S. near the coast : known by the small size 

 (1 -.3' high), few flowers, usually only one of them fertile and rrcurved in fruit ; 

 stamens only about 7, with glabrous filaments ; akenes obovate, with erect beak ; 

 and leaves without a true blade. 



S. natans, only S. is probably a large state of the last, with leaves having 

 a floating blade l'-2' long, ovate or oblong, or slightly heart-shaped, 5-7 

 nerved. 



6. LIMNOCHARIS. (Name from the Greek means delight of the pools.) 



L. Humbbldtii. Tender aquatic plant from S. America, which, turned 

 into pools, spreads widely by its proliferous branching and rooting stems, and 

 flowers all summer and autumn ; each flower lasting but a day, the 3 broad 

 sulphur-yellow petals !'-!' long; pistils about 6; leaves about 3' long, the 

 midrib swollen below. 



115. HYDROCHARIDACE^S, FROG'S-BTT FAMILY. 



Water-plants, with dioecious, monoecious, or polygamous flowers 

 on scape-like peduncles from a sort of spathe of one or two leaves, 

 the perianth in the fertile flowers of G parts united below into a 

 tube which is coherent with the surface of a compound ovary : we 

 have three plants, two of iliein very common. 



* Floatiny, spreading by prol/fi-rons sltoots ; leaves lonrj-petiolcd, rounded heart-shaped. 

 I. LIMNOBIUM. Flowers monoecious or dioecious, from sessile or short-stalked 



leaf-like spathes, the sterile spathe of one leaf surrounding 3 long-pedicelled 

 staminate flowers: the fertile 2-leaved, with one short-pedicelled flower. 

 Perianth of 3 outer oval lobes (calyx) and 3 narrow inner ones (petals). A 

 cluster of 6-12 unequal monadelphous stamens in the sterile flower: srme 

 awl-shaped rudiments of stamens and a 6-!>-ce!led ovary in the icrtile 

 flower; stigmas 0-9, each 2-parted. Fruit berry-like, many-seeded. 



* * Growing umltr water, the fertile flowers only rising to the surf nee ; the sterile 



(not often detected) breaking offtktir short slttlksj and jlotttiny on the surface 

 around the pistillate Jlotoert. 



1. ANACHARIS. Stems leafy and branching. Fertile flowers rising from a tubu- 

 lar spathe; the perianth prolonged into an exceedingly slender stalk-like 

 tube, 6-lobed at top, commonly bearing 3-9 apparently good stamens : ovary 

 1-celled with a few ovules on the walls: style coherent with the tube of the 

 perianth: stigmas 3, notched. 



3. VALLISNEBIA. Stemless ; leaves all in tufts from creeping rootstocks. Fer- 

 tile flowers with a tubular spathe, raised to the surface of the water on an 



21 



