234 TETRANDRIA— TETRAGYNIA. Potamogeton. 



or 3 inches long, and 1 -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- 

 ceolatuni. 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. 



10. V. cuspidatum. Pointed-leaved Pond-weed. 



Leaves linear, with an oblique taper point; three principal 

 ribs, and numerous intermediate ones, all distinct. Stem 

 compressed. 



P. cuspidatum. Schrad. Germ. v. 2. 



P. compressum. Teesdale Tr, of Linn. Soc. v. 2. 106. Don H. 

 Br. 204. 



P. gramineum latifolium. Loes. Pruss. 206. t. 66 ; excellent. 



In ponds and rivulets. 



In a rivulet at Hovingham, Yorkshire. Mr. Robert Teesdale. In 

 the lake of Rescobie, and also in the lake of Forfar. Mr. G. Don. 



Larger than the last, with which it has, in England, always been 

 confounded. Professor Schrader has communicated it to me as 

 the P. cuspidatum of his H. Germ., the 2d vol. of which, if pub- 

 lished, has not yet reached us, and 1 have sought out such cha- 

 racters as my specimens afford. The principal one is indicated 

 in the name. The leaves are not rounded at the end, but taper 

 off rather suddenly and obliquely, into a terminal point, formed 

 of the substance of the leaf. There are, moreover, only 2 lateral 

 ribs, 1 at each side, half way between the mid-rib and the mar- 

 gin. These are often very inconspicuous ) but there are nume- 

 rous intermediate ribs, all over the leaf, which do not occur in 

 P. compressum. Both the lateral as well as all the intermediate 

 ribs keep distinct, and vanish just below the extremity of the 

 leaf. These characters, though not the intermediate ribs, are 

 clearly expressed in Loesel's figure, which has hitherto been 

 quoted for P. compressum, as has likewise Haller's n. 85 1 . But 

 his character of the lanceolate leaves long ago caused the accu- 

 rate Mr. Davall to suspect an error in that reference. This cha- 

 racter indeed agrees admirably with specimens in the Linnsean 

 herbarium, of a plant erroneously taken for compressum, but 

 which I am told the late Professor Willdenow has somewliere 

 named complanatum. \i% Jlower-stalks are near a foot long ; 

 /eaics 5 -ribbed, l-3d of an inch broad, tapering at each end. 

 This is very possibly Holler's w. 851. 



