PETALOLDE^. 



691 



Fig. 1070. 



Fig. 1071. Fig. 1072. Fig. 1073. 



Fig. 1070. Two flowers of the Horned Pondweed {Zannichellia palustris\ one 

 staminate, the other pistillate Fig. 1071. The pistil of the same, com- 

 posed of four perfect carpels, and one imperfect Fig. 1072. Vertical 



section of the ovary of the same. Fig. 1073. Vertical section of the fruit 

 and seed. All magnified. After Lindley. 



Distribution, ^c. — Chiefly found in extra-tropical regions. 

 Examples : — Xaias, Zannichellia. They have no known uses. 



Natural Order 278. Zosteeace^. — 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 usually, by the 

 complete absence of a perianth. 



Distribution, ^c. — They are widely distributed in the ocean 

 in various quarters of the globe. Examples : — AmphiboUs, 

 Zostera. There are 5 genera, and 12 species. Their properties 

 are of little importance. Zostera marina, Sea-wrack, is in 

 common use for packing, and for stuflSng chairs, mattrasses, &c., 

 under the name of Alva (Ulva or Alga) marina. 



Natural Order 279. Triuridace^. — The Triuris Order. — 

 Diagnosis. — This is a small order of plants closely allied to 

 Naiadacese, but usually to be distinguished by its rudimentary 

 embryo. The flowers are, however, sometimes perfect. 



Distribution, ^c. — Exclusively found in warm and tropical 

 regions. — Examples .- — Triuris, Sciaphila. There are 5 genera, 

 and 8 species. 



Their properties and uses are unknown. 



Natural Order 280. Htdrocharidace^. — The Hydrocharis 

 or Frog-bit Order. — Aquatic plants. Flowers spathaceous, 

 regular, dioecious or polygamous. Perianth superior, in 1 



T Y 2 



