484 



CV. NAIADACE^. 



[Potamogeton. 



differing only in their firmer texture and in being stalked ; the ribs 

 shape, and size are nearly alike in both. The lateral ribs or nerves 



are by no means separate to the base of the leaf, but arise from various 

 parts of the central rib, some of them one third the length of the leaf 

 from its base ; they are from 6 — 7 in number on each side, 2 of them 

 more evident than the rest: flower-stalk not thickened upwards-" 

 Wilson in litt. The plant is remarkable for its reddish-olive colour 

 and is perhaps better known by its general aspect, size, and hue, thau 

 by any character that can be applied to it. — To us, the above species 

 Avith floating leaves seem gradually to pass into one another. 



■ 



17. P. plantagineus Ducr. (Plantain-leaved P.); leaves all 

 membranous stalked, lower ones oblong, upper " elliptical 

 achenes minute obliquely ovate rounded on the back when 

 recent acutely keeled when dry, spike slender cylindrical 

 densely-flowered, peduncle lonp^ not thickened upwards. 

 E. B. S. t^ 2848. P. coloratus Horn. : Cham, and SchL I. c 

 p. 194. 



Deep peaty pits and ditches, probably far from rare. ' Vazon Bav, 

 Guernsey. Norfolk, Cambridgeshire, Kent. Ferneyrig Loch,Eccles, 

 Berwickshire. 6, 7. — It has usually been confounded with P. nafansj 

 from which it may be discriminated by its beautifully diaphanous 

 reticulated leaves, none of which are coriaceous, and its much smaller 

 fruit. It is more nearly allied to P. ohhngus, from which its leaves, 

 as well as the acutely keeled back of the fruit when dry, clearly dis- 



tinguish it 



in that plant the fruit is always obtuse : Bah, 



18. P. ohlongus Yiv. {ohlong -leaved P.)-, "leaves all stalked, 

 upper ones coriaceous floating oblong-elliptical, lower linear- 

 lanceolate, achenes minute with their back always obtuse and 

 rounded, spike slender cylindrical densely-flowered upon a long 

 terete peduncle." Bah. : E. B. S. t. 2849. P. natans t. Mert 

 and Koch. 



m 



" Far from uncommon, in wet ditches, small streams, ponds and 



Frequent in Scotland. 1^. 7. 



bogs." 



^* It is distinguished from 



P. natans, with which most botanists probably confound it, by the 

 form and size of its fruit, as well as by other characters : " Bab. We 

 fear some of the above characters taken from the fruit are not constant, 

 for we have examined specimens where the achenes were decidedly 

 marked on the back with 3 ridges, the middle one being acute. It 

 is found usually in bogs and ditches almost dry in summer; — may 

 not this sufficiently explain why the fruit is not above half the size of 

 that of the next species? 



19. P. natans L. (sharp-fruited broad-leaved P.); lower 

 leaves linear submembranaceous or wanting, upper elliptical 

 coriaceous floating on long stalks many-neA^ed distinctly cel- 

 lular, fruit (large) keeled at the back. E. B. t. 1822. 



Stagnant waters and slow streams, frequent. 11. 6, 7. — Very 

 variable in general size, and in the shape of its floating leaves 



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