936 TETRANDUIA— TETRAGYNIA. Potamogeton. 



In ditches near Deptford. Buddie. Near Norwich. Mr. Rose. In 

 the ponds at Castle Howard, and near Beverley, Yorkshire. 

 Mr. Teesdale. 



Perennial. July. 



Herb submersed. Stem slender, thread-shaped, wavy, much branch- 

 ed, forked in the upper part. Leaves grassy, alternate, except 

 at the forks, crowded, spreading, 3 inches long, of a fine green, 

 linear, though gradually contracted toward the base, bluntish, 

 with an occasional small short point. Their mid-rib is more or 

 less accompanied by very narrow, oblong, parallel reticulations j 

 side ribs solitary, nearer to the margin than to the mid-rib, ex- 

 tremely fine, and sometimes scarcely discernible, vanishing at a 

 greater or less distance below the point. There are no inter- 

 mediate ribs. Stipulas pale, usually convoluted, so as to be nar- 

 rower than their leaves. Stalks from the forks of the stem, per- 

 haps without exception ; the remark to the contrary, in some 

 instances, being founded on a specimen of P. cuspidatum, mis- 

 taken by Linnaeus. Spikes ovate, dense, generally quite as long 

 as their stolks, just raised above the water. Seeds almost glo- 

 bular, with an oblique point. 



The ribs of the leaves in this and the two preceding species will 

 always clearly ascertain them. They have indeed puzzled bo- 

 tanists who have seen them only superficially, or not at all 5 but 

 they are not the less distinct on that account. 



12. Y.pusillum. Small Pond-weed. 



Leaves linear, spreading at the base, opposite or alternate, 

 with solitary, very slender, lateral ribs. Stem round. 

 Flower-stalks axillary, mostly lateral, many times longer 

 than their spikes. 



P pusillum. Linn.Sp.Pl.\84. Willd.vA.lM . Fl. Br. 197. Engl. 

 Bot.v.3.t.2\5. Hook.Scot.59. Ehrh.Herb.W2. Fl. Dan.t.\45\. 



P. n.852. Hall. Hist. v. 1.377. 



P. pusillum, gramineo folio, caule tereti. Rail Syn. 150. Vaill. 

 ' Par. 164. t. 32./. 4. 



P. gramineum tenuifolium. Loes. Pruss. 206. t. 67. 



Narrow Grass Pond-weed. Petiv. H. Brit. t.5.f.\\. 



In ponds and ditches, especially on a clay soil, not uncommon. 



Perennial. July. 



Much smaller than any of the foregoing. Stem slender, round, 

 more or less branched, from 1 to 2 feet long, altogether sub- 

 mersed, the flowers only appearing above water. Leaves 1£ or 

 2 inches long, scarcely a line in breadth, opposite under every 

 flower-stalk, otherwise alternate, rather acute 5 their mid-rib 

 slightly accompanied by oblong reticulations ; lateral ribs to- 

 wards the margins, solitary, very slender, and often hardly visi- 

 ble ; if continued far enough, joining the mid-rib, at some di- 



