frog's-bit tamilt. 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 ; 

 almost all the well-developed leaves arrow-shaped ; filaments neai-ly twice the 

 length of the anthers, smooth; akenes broadly obovate, vrith a long and 

 curved beak ; calyx remaining open. 



S. calyclua. 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 vrith 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. 



* * JFilaments very short and broad. 



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

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

 pubescent ; akenes narrow-obovate, with a long erect 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 recurved in fruit ; 

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

 and leaves without a true blade. 



S. nutans, 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. LIMITOCHAKIS. (Name from the Greek means rfe%A« o/'«Ae/)oo&.) 



Ii. Humbdldtii. 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 I'-lJ'long; pistils about 6; leaves about 3' long, the 

 midrib swollen below. 



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

 Water-plants, with dioecious, moncecious, or polygamous flovyers 

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

 the perianth in the fertile flowers of 6 parts united below into a 

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

 have three plants, two of them very common. 

 « Floating, spreading by proU/erom ihoots ; haves long-petioled, roimded heart-shaped. 

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

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

 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 6-9-oelled ovary in the lertile 

 flower; stigmas 6-9, each 2-parted. Fruit berry-like, many-seeded. 

 • • Growing under water, the fertile Jloiliers only rising to the mrfnce ; the sterile 

 {not often detected) breaking off their short stalks, and floating on the smrfaee 

 aroimd the pistillate flowers. 

 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 waUs: style coherent with the tube of the 

 perianth : stigmas 3, notched. 

 3. VALLISNEEIA. Stomless ; leaves all in tufts from creeping rootstocks. Fer- 

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

 21 



