FROG-BIT FAMILY 457 



or bast, the vessels being grouped in scattered bundles which 

 are most numerous near the outside of the stem, which, in con- 

 sequence, is hardest near the exterior and sometimes hollow in the 

 centre, especially among the Grasses. The leaves are generally 

 simple, entire, and smooth, with parallel veins, or a regular net- 

 work formed by transverse veins which are much finer than the 

 longitudinal ones. The flowers are often destitute of a perianth, 

 the place of which is supplied by hard, chaffy scales known as 

 glumes. The sepals and petals, when present, the stamens and the 

 carpels are generally 3, or some multiple of 3, in number. 



Sub-Class I. PETALGTDE^E 



Flowers usually furnished with a petaloid and coloured, not a 

 green or glumaceous, perianth. 



Series I. EPIGYN.E.— Ord. LXXVIL— LXXXI 



Perianth superior ; ovary inferior 

 Ord. LXXVII. HYDROCHARfDEiE. — The Frog-bit Family 



A small Order of aquatic plants, often floating, with con- 

 spicuous, polysymmetric, dioecious flowers, enclosed, when in bud, 

 in a sheath, or spathe ; sepals 3, green ; petals 3 ; stamens 3 — 12 ; 

 carpels 3 — 6, united into an inferior, 1- or many-chambered ovary ; 

 style 1 ; stigmas 3 — 9 ; fruit indehiscent, generally a berry, 1- or 

 many-chambered. Only three members of the Order occur in 

 Britain, belonging to three different genera. 



*i. Elodea. — Leaves submerged, linear, whorled. 



2. Hydr6charis. — Leaves orbicular, floating. 



3. Stratiotes. — Leaves submerged ; sword-shaped, serrate. 



*i. Elodea canadensis (American Water-weed, Water-thyme). 

 — A submerged, dark-green, translucent plant, with a long, slender, 

 branching, brittle stem, rooting at its nodes ; leaves in whorls 

 of 3, linear-oblong, finely serrate; flowers floating, small, pink, 

 dioecious, only the carpellate form commonly occurring, which 

 has a very slender perianth-tube 4 — 8 in. long ; 3 sepals ; 3 petals ; 

 3 staminodes ; ovary 1 -chambered ; style slender ; stigmas 3, 

 ligulate. — Rivers, canals, and ponds ; common. Introduced 

 from America between 1836 and 1841. (Name from the Greek 

 helodes, swampy.) 



2. Hydrocharis (Frog-bit), represented only by the one 

 species H. Morsus-rdnce, a floating plant with creeping stems; 

 roundish, cordate, stalked, floating leaves ; and delicate white 



