66 NAIADES. [CI. 1. 



two valves, either naked, or bound by a transverse 

 elastic ring. Seeds very minute, readily germina- 

 ting, and so abundant, that many a species, if its 

 possible increase were uninterrupted for 20 years, 

 might cover the whole earth. The forms and situ- 

 ations of the Sorij and the direction in which the 

 Involucrum separates, afford generic characters, un- 

 known when Jussieu published. 



Poli/podium has no Involucrum; Aspidium a round- 

 ed one; Pteris a continuous marginal one, separating 

 inward; Lindscea the reverse. 



Orel. 6. Naiades. " Calyx either entire or divided, 

 superior or inferior, rarely wanting. Stamens definite, 

 perhaps perigynous (97). Germen superior or infe- 

 rior, solitary or four-fold. Style 1, rarely 2, to each 

 Germen, or wanting. Stigma one or several. Seeds 

 solitary or several, either naked and superior, or in- 

 closed in a Pericarp which is either superior or infe- 

 rior. Leaves mostly opposite or whorled. Flowers 

 in some perfect (65), in others monoecious or dioe- 

 cious. Plants all herbaceous, and, except Satirurus, 

 aquatic." The uncertainty of this Order has been al- 

 ready noticed, (92), and the characters, above given, 

 have so many ambiguities as to amount scarcely to 

 any thing. The Genera are, Hippuris, fig. 252, 

 Cham, Ceratophyllum, Myriophyllum, fig. 251, 

 Naias, Saururus, Aponogeton, fig. 134, Potamoge- 

 ton, fig. 135, Ruppia, Zannichellia, Callitriche, and 

 Lenina, fig. 136. Naias, Lemna, and Chara, are 

 judged by Mr. Brown to be akin to his Hydro- 



