TETRANDRTA. TETRAGTNIA. Ill 



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

 Caiix 4~Ieave<J. Corolla 0. Style 0. Seeds 4. 



Leaves sheuihing, those of the stem often alternate, flo- 

 ral leaves mostly oppositt-; fi >uers spiRed, terminal or 

 axillary; rac uli and bpikes having frequently 2 sheathes 

 at :he base. Nut 1-seedeci, cochleate; enibryon erect, 

 cxaibuminous, curvt d or involute. 



Species. 1. P. nutans. i.Jlxdians. 2. heterophyllum. 4. 

 setaceum. 5. perfoliatiim. 6. lucens. 7 • crispim. 8. grami- 

 ncnm. 9. pectinatum.—\ genus of aquatic plants, appa- 

 rently confined to Europe and North America; those of 

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

 rope. 



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



Calix none. Corolla none. Seeds 4, pedicel- 

 late. 



A maritime aquatic plant with capillary branches; leaves 

 gramintous, sheathing-; on the stem alternate, towards tlie 

 flower nearl} opposite; flowers in a spikelec or spadix, so- 

 litary, mostly terminal, distichal, peduncle convolute, 

 stretching or contracting accordmg to the depth of water, 

 after the manner of Valisneria-, "calix 2-valved, aecldu- 

 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 tiie nature of 

 tlie loot.f 



Species. 1. R. maritir.ia. Common probably to every 

 part of the world. 



t Being distinct from the ordinary cotyledons, albumen or 

 perisperm, to distingish it fi-om them I propose the name of 

 eomarliize, i^somarhizai or a radical inactive oody 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 extraneoas perisperm in its vascular connection 

 wiih the embryon. 



