1863.] PONDWEEDS. 465 



opposite. The stipules are sometimes united to each other and 

 sometimes are joined to the leaf-stalk and form a sheath which 

 embraces the corresponding branch of the stem. The flowers are 

 in axillary or terminal spikes, or solitary or clustered in the axils 

 of the leaves. The perianth consists of four herbaceous (uot 

 coloured) processes. Note. — This organ is not always present; 

 sometimes^ in Ruppia, for example, its place is supplied by a 

 membranous spathe or sheath. The stamens are four, or only 

 one, inserted at the base of the segments of the perianth. The 

 anthers are sessile, (on long filaments in Ruppia,) with a more or 

 less thick connective, opening by a longitudinal fissure. Ovary 

 free, consisting of four carpels, each bearing one ovule. Pericarp 

 coriaceous or fleshy. Seed with a membranous covering (testa) 

 without albumen (consisting of the gcrmen only). Embryo folded 

 or rolled on itself. Radicle near the hilum or opposite. 



PoTAMOGETON. — The Ordinal description almost defines this 

 the principal genus of the Order. The flowers are all herma- 

 phrodite or perfect ; style very short, with a peltate (enlarged) 

 stigma. The carpels are normally four, but often fewer by abor- 

 tion. The fruit (carpels) are more or less beaked. 



The principal genus, Potamogeton, may conveniently be sepa- 

 rated into two groups or sections, viz. (1) the broad-leaved, and 

 (2) the narrow-leaved species, or the Plantain-leaved and the 

 Grass-leaved kinds. Each of these primary groups may be natu- 

 rally subdivided into (1) coriaceous, or rather opake or transpa- 

 rent-leaved species, leathery-leaved species, and (2) the pellucid 

 or shining-leaved. 



1. P. natans, Linn. The best-known and most generally 

 distributed of the genus has round, striated, or slightly ridged 

 and furrowed stems, which are as thick as strong pack-thread 

 or about one- eighth of an inch in diameter. They are either, 

 long or short, their extent depending on the distance between the 

 surface of the water, and the bottom of the pond or other piece 

 of water where they grow. From the joints of the stem either 

 rootlets or leaves or branches are produced. These joints or 

 junctions in the stem are furnished with scarious processes 

 called stipules and sheaths; the former, viz. the stipules are from 

 half an inch to an inch long, and lanceolate in shape, clasping 

 the leaf-stalk; the sheaths are from three to four or five inches 

 long, and clasp closely the branch or the fruit-stalk (peduncle) . 



N. S. VOL. VI. 3 O 



