HYDROCllAKIUACE^. (FROG'S-BIT FAMILY 495 



Class II. MONOCOTYLEDONOUS ok ENDOGENOUS 



PLANTS. 



Steiii.s with no manifest distinction into bark, wood, and 

 pitli, but the woody fibre and vessels in bundles or threads 

 which are irregularly imbedded in the cellular tissue ; peren- 

 nial trunks destitute of annual layers. Leaves mostly parallel- 

 veined (nerved) and sheathing at the base, seldom separating 

 by an articulation, almost always alternate or scattered and 

 not toothed. Parts of the flower commonly in threes. Em- 

 bryo with a single cotyledon, and the leaves of the plumule 

 alternate. 



Order 108. HYDROCHARIDACE^E. (Frog's-bit Family.) 



Aquatic herbs, ivilh dioecious or polygamous regular flowers, sessile or on 

 scape-like peduncles from a spathe, and simple or double floral envelopes, 

 which in the fertile flowers are united into a tube and coherent icith the 1 - 

 ^-celled ovary. Stamens 3-12, distinct or monadelphous ; anthers 2-celled. 

 Stigmas 3 or 6. Fruit ripening under water, indeliiscent, many-seeded. 

 Seeds ascending, without albumen ; embryo straight. 

 Tribe I. HYDIIIL,L.E^. Stem elongated, submerged, leafy. Spathes small, sessile. 



1. Elloclea. Leaves verticillate (rarely opposite). Perianth-tube long-filiform. 



Tribe II. VALLISNEKIEiE. Stemless. Leaves elocgated. Spathes pedunculate. 



2. VaUisneria. SuVmierged ; grass-like. Fertile flower solitary on a very long scape. 



Tribe III. STKATIOTE^. Stem very short, with crowded leaves. Spathes pe- 

 dunculate. Ovary 6-9-celled. 



3 ILiuinobiuui. Stemless, floating; broad leaves long-petioled. 



1. ELODEA, Michx. Water-weed. 



Flowers polygamo-dioecious, solitary and sessile from a sessile tubular 2-cleft 

 axillary spathe. Sterile flowers small or minute, with 3 sepals barely united 

 at base, and usually 3 similar or narrower petals ; filaments short and united 

 at base, or none ; anthers 3-9, oval. Fertile flowers pistillate or apparently 

 perfect ; perianth extended into an extremely long capillary tube ; the limb 

 6-parted ; the small lobes obovate, spreading. Stamens 3-9, often with im- 

 perfect anthers or none. Ovary 1 -celled, with 3 parietal placentae, each bear- 

 ing a few orthotropous ovules ; the capillary style coherent with the tube of 

 the perianth ; stigmas 3, large, 2-lobed or notched, exserted. Fruit oblong, 

 coriaceous, few-seeded. — Perennial slender submerged herbs, with elongated 

 branching stems, thickly beset with pellucid and veinless, 1 -nerved, sessile, 

 whorled or opposite leaves. The staminate flowers (rarely seen) commonly 

 break off, as in Vallisneria, and float on the surface, where they expand and 

 slied their pollen around the stigmas of the fertile flowers, raised to the surface 



