273 



NOTES ON POND WEEDS. 



By Alfred Fryek. 



Potamogeton fluitans Eoth. Stem springing from a rootstock 

 which strikes deeply into the mud, and is sometimes thickened into 

 tubers ; stout, 2-5 ft. long, usually branching a little below the 

 middle, or simple in the summer shoots, rarely branched from the 

 base. Leaves of three kinds, those of the lower part of the stem 

 reduced to phyllodes, those of the middle, ynembranous, elongate, 

 narrowly lanceolate, submerged ; those of the upper part, coriaceous, 

 floating, oblong-lanceolate or elliptical ; all long-stalked, with 

 petioles convex above. Stipules large, deeply channelled on the back, 

 slightly winged, rather acute, very persistent. Spikes densely flowered, 

 1-1^ in. long, stout, on peduncles which are of equal thickness 

 throughout, or slightly swollen upwards. l^nuY (immature), 3-keeled, 

 with the central keel rather prominent. 



P. fluitans starts into growth early in the year ; the earliest 

 leaves are reduced to phyllodes, which resemble those of the 

 /ttmzs-group, being short, 1^-6 in., always submerged, and per- 

 sistent. Thus differing from the long, floating, quickly-decaying 

 phyllodes of P. natans. These phyllodes are produced throughout 

 the whole period of growth, though they are more abundant early 

 in the season, and are sometimes absent in the later shoots. 

 Usually only one or two are present at the base of the stem, but in 

 deep water as many as five or six are occasionally found. Like the 

 true leaves, the phyllodes are stalked, which is apparent in fresh 

 examples by the lower part being slightly convex, while the upper 

 part is very slightly concave; in dried specimens these minute 

 differences are lost. The phyllodes gradually pass into the ordinary 

 submerged leaves by intermediate bodkin-pointed leaves, of which the 

 petiole and midrib are thick and fleshy as in the simple phyllode, 

 but the midrib is expanded into a narrow wing for an inch or two 

 above its junction with the petiole, and then is reduced to a long 

 bodkin-like point. Here again P. fluitans approaches P. lucens, in 

 which similar bodkin-pointed leaves are constantly produced. 



The submerged leaves which next follow strongly characterize 

 the species, as they are unlike those of any other British Pond weed ; 

 they are translucent, membranous, narrowly lanceolate, 6-12 in. 

 long by £-£ in. wide, tapering gradually into the convex petiole, 

 which is 2-2£ in. long, slightly folded, with a stout prominent 

 midrib, with two or three faint, translucent, lateral ribs, which are 

 not raised above the surface of the leaf, and which are connected 

 by transverse veins ; on each side of the midrib is a narrow band 

 of elongate chain-like aerolations. These elongate secondary leaves 

 ar e usually submerged, but as the stem lengthens many of them 

 rise to the surface and assume the coriaceous texture of the true 

 floating leaves which they gradually pass into, and together spread 

 lj ke a fan on the surface of the water. 



The true floating leaves are thick, coriaceous, with a thick 

 Prominent midrib, with 5-7 lateral ribs on each side, which are 



Journal of Botany.— Vol. 26. [Sept., 1888.] x 



