$94 TETRANDRIA— TETRAGYNIA. Potamogeton. 



P. n. 848. Hall. Hist. v. 1. 376. 



P. seu Fontinalis crispa. Raii Syn. 149. Bauh. Hist. v. 3. 770./. 



Tribulus aquaticus minor, quercfis floribus. Ger. Em. 824./. 



Pusillum Fonti-lapathum. Lob. Ic. v. 1. 286./. 



/3. Potamogeton scrratum. Huds. 75 ; excl. perhaps all the syn. 



Tribulus aquaticus minor. Clus. Pann. 7\3.f.7\4 #715. Hist. 

 v.2.252.f. 



T. aquat. minor, muscatellae floribus. Ger. Em. 824./. not descrip- 

 tion. 



In ditches, ponds, and rivulets, frequent. 



Perennial. June, July. 



Whole plant under water, bright green. Leaves sessile, or nearly 

 so, 2 inches long, bluntish, elegantly crisped at the edges, and 

 more or less undulated ; furnished with slight reticulations next 

 the rib, far less remarkable than the last. The lower leaves are 

 usually alternate} upper ones often opposite. Fl. yellowish 

 green, with elongated reddish styles, in short loose spikes. Hud- 

 son's P. serratum is acknowledged by himself to be too near 

 crispum, of which it is doubtless a variety with more of the leaves 

 opposite, and all perhaps less undulated ; as in Clusius's figure, 

 annexed by Johnson, in Gerarde, to a description belonging to 

 P. densum. 



9. P. compression. Flat-stalked Pond-weed. 



Leaves linear, obtuse, with a very slight point; two lateral 

 ribs meeting just below the extremity. Stem compressed. 



P.compressum. Linn. Sp. PI. 183. Willd.v.\.7\b. Fl.Br.X9b. 

 Engl. Bot. v. 6. *. 418. Hook. Scot. 58. Fl. Dan. t. 203. 



P. caule compresso, folio graminis canini. Raii Syn. 149. Dill. 

 Giss. 112. 



In ditches and slow streams. 



Perennial. June, July. 



Stem wavy, alternately branched, much compressed throughout its 

 whole length, though rounded at the edges. Leaves sessile, al- 

 ternate, except a pair or two of the uppermost, perfectly linear, 

 in which this species differs from all the preceding j they are 2 

 or 3 inches long, and l-8th of an inch broad, rounded at the 

 end, with a minute, often scarcely perceptible, point. The mid- 

 rib becomes cellular, or vascular, in the upper leaves, as if com- 

 posed of oblong reticulations, in some degree resembling P. lan- 

 ceolatum. Whether this appearance be owing to air-vessels, 

 produced in the flowering season, to render the plant buoyant, 

 we can but conjecture. At each side are 2 equidistant, parallel, 

 very fine ribs, of which the inner pair only are continued till they 

 form an arch just below the termination of the leaf. Stipulas 

 pale, partly cloven, embracing the stem. Flowers brownish, 4 

 or more in each small loose spike, just rising out of the water, 

 terminal till the branch rises above them. 



