TETRANDKTA. TETRAGTNIA. Ill 



166. POTAMOGETON. L. (Pond-weed.) 



Calix 4-leaved. Corolla 0. Style 0. Seeds 4, 



Leaves sheaihing-, those of the stem often alternate, flo^ 

 ral leaves niostiy opposite; fi wers spiKed, terminal or 

 axillary; ra'iuli and spikes having' frequently 2 sheathes 

 at the base. Not 1-seeded, cochleate; embryon erect, 

 exatbuminous, curved or involute. 



Species. 1. P. nutans. 2.Jiuitans. 3. heterophylh/m. 4» 

 setaceuin. .5. perfo'datnm. 6. lucens. 7. anspun. b. grami- 

 noim. 9. pecHnaiwn. — A genus »f aquatic plants, arpa- 

 rently confined to Europe and Norih America; tivse of 

 the latter continent at the same time common also to Eu» 

 rope. 



167. RUPPIA. L. (Tiissel Pond-weed.) 



Calix none. Corolla nunc. Seeds 4, pedicel- 

 late. 



A maritime aquatic plant with capillary branches; leaves 

 gramineous, sheathing; on the stem alternate, towards the 

 flower nearly opposite; flowers in a splkelet or spad;x, so- 

 litary, mostly terminal, distichal, peduncle convolute, 

 stretching or contracting according to the depth of w^ater, 

 after the manner of Valisnena; *' calix 2-valved, decidu- 

 ous," JussiEu. Fruit subulate, when mature incurved at 

 the point. Nut gibbous, containing one seed; embryon 

 erect, attached (as in many other plants of the same natu- 

 ral class,) to a germinal body apparently of the nature of 

 the root.-}- 



Species. 1. R. maritima. Common probably to every 

 part of the world. 



I Being distinct from the ordinary cotyledons, albumen or 

 perisperm, to distingish it from them I propose the name of 

 somarhize, {^somarhiza) or a radical inactive body affording a 

 temporary nourishment to the embryon with which it possesses 

 a simple vascular connection, but without producing any spe- 

 cies of radicles or leaves, often in the form of a cohering cal- 

 lous tubercle, it exists longer than ordinary cotyledons, and dif- 

 fers from an extraneous perisperm in its vascular connection 

 with the embryon. 



