466 poxDWEEDs. [March, 



The leaves, which are poly raorphous (of many figures, from ovate 

 to elliptical-lanceolate) , are opposite, on either long or short stout 

 foot-stalks ; they have on the under side a prominent midrib, 

 with three, four, or five less prominent lateral ribs on each side of 

 the main one, which is the prolongation of the leaf-stalk. 



The spaces in the leaf between the ribs are filled up by nume- 

 rous secondary ribs more or less prominent, and the whole frame- 

 work is bound together by a close network of short nerves or 

 fibres, which appear when the fleshy part of the leaf is dissolved 

 like a bit of very fine lace. The upper side of the leaves is flat ; 

 the margin is quite entire, and the apex, or top, is furnished with a 

 short blunt point. The peduncle or flower and fruit-stalk is fully 

 as thick as the stem, and is more or less tapering and of unequal 

 length, but always longer than the spike. The spike is cylin- 

 drical, dense, one and a half to two inches in length, and the 

 smooth fruit is furnished with a stout, lateral apex (point). This 

 is the commonest of all the Pondweeds. 



2. P. polygonifolius, Pourret, — P. oblongus, Viv., — differs but 

 slightly from the above. The chief distinctions are locality and 

 size. It is the commonest Potamogeton of moory, moist, or springy 

 places, and in shallow ditches, peat bogs, fens, etc., where the 

 depressions are full of vegetation. Its colour is often reddish ; 

 its foliage is of a broader and shorter character, and the peduncles, 

 spikes, and fruit are smaller than in the preceding species. It is 

 P. natans, var. 2, of Dr. Withering's botanical arrangement. 

 The excellent author of the ' English Flora ' does not notice it 

 even as a variety. 



Note. These two species or varieties are easily distinguished 

 when growing in their proper localities and in their normal state ; 

 but large forms of the latter, P. polygonifolius, when taken from 

 deep ditches and ponds, scarcely differ from small forms of P. 

 natans : in the herbarium they are barely distinguishable. 



3.- P. plantagineus, Ducroz, in some respects is more closely 

 allied to P. natans than to P. lucens. Its leaves are broader than 

 in P. natans, but not longer, and they are floating, or part of 

 them appear above water ; their colour is greenish-olive, and 

 their longitudinal ribs are connected by more conspicuous, trans- 

 verse, connecting nerves. Its spike is smaller, and it is besides a 

 very rare species. It grows in many parts of Europe, from the 

 Baltic to the Mediterranean. 



