PETALOIDE.^. 



695 



hiscent, or sometimes dehiscent. Embryo straight, cleft, in the 

 axis of fleshy albumen. 



Distribution, <^-c. — They inhabit cool, temperate, and tropical 

 regions. Examples of the Genera: — Lemna, Pistia. There are 

 above 20 species. Their properties are imimportant. 



Natural Order 277. Naiadace^i^. — The Pondweed Order 

 {fgs. 1071-1074). — Character. — Aquatic plants with jointed 

 cellular stems. Leaves with interpetiolar membranous stipules. 

 Flowers small, unisexual {figs. 1071 and 1072). Perianth either 

 wanting, or composed of 2 or 4 parts. Stamens few, hypogy- 

 nous; pollen globose. Ovaries 1 or more, superior {fig. 10/2) ; 

 ovule solitary {fig. 1073). Fruit 1-celled, 1-seeded {fig. 1074). 

 Seed exalbuniinous {fig. 1074) ; embryo with a lateral cleft. 



Fig. 1071 



Fig. 1072. 



Fig. 1074. 



Fig. 1071. Two flowers of the Horned Ponclweed (ZamiiclielUa palustris), 



i)i)estamiiiate, the other pistillate. F/g. 1072. The pistil of the same, 



composed of four perfect carpels, and one imperfect. Fig. 1073. Ver- 

 tical section of one of the carpels. Fig. 1074. Vertical section of 



the fruit and seed. All magnified. After Liudley. 



Distribution, cfr. — Chiefly found in extra-tropical regions. 

 Examples of the Genera : — Naias, Zannichellia. They have no 

 known uses. 



Natural Order 278. Zosterace;e. — The Sea-wrack Order. — 

 Diagnosis. — This is a small order of marine plants with the 

 habit of sea-weeds. They are usually associated with the 

 Naiadacese, but from which they are principally distinguished 

 by their filamentous or confervoid pollen, and also, commonly, 

 by the complete absence of a perianth. 



Distribution, cfc. — They are widely distributed in the ocean 

 in various quarters of the globe. Examples of the Genera: — : 



