88 



NOTES ON PONDWEEDS. 



By Alfred Fryer. 

 (Plates 317 & 818.) 



PoTAMOGfc'tON G&AMINEUS L. V, GRAMINIFOLIUS Fries = P. HETERO- 



fcHYLLUs var. — Bootstock with many strong far-creeping stolons. 

 Stem stout, terete, flexuous, ascending, dichotomously branched 

 from the base, sometimes with secondary branchlets. Stems with 

 wholly submerged foliage, slender, and more crowded together; 

 internodes elongated, but shorter than their subtending leaves. 

 Lower leaves all similar, flat, sessile, ascending, alternate, thin, 

 somewhat opaque, shining; strap-shaped, or elongate-lanceolate, 

 attenuated towards each end, especially towards the acute acuminate 

 apex, often falcate ; lowest rarely reduced to a centrally-expanded 

 bodkin-pointed midrib. Floating coriaceous leaves alternate, 

 stalked, oval-elliptical or oblong; lamina gradually or suddenly 

 contracted into the petiole, which it usually exceeds in length ; 

 rarely produced in a depauperated state at the base of the peduncles, 

 and then opposite, essentially belonging to barren states of the 

 plant. Stipules persistent, herbaceous, small, narrow, becoming 

 involute and then appearing acute, larger and broader on autumnal 

 barren stems, cymbiform beneath the peduncles. Flower-spikes 

 dense, cylindrical, 1-1 i in. long, few, usually produced singly, 

 terminal. Drupelets small, compressed, green, shining; dorsal 

 margin semicircular, acutely keeled ; lateral ridges less conspicuous; 

 inner margin slightly convex ; beak short, subcentral. Whole plant 

 bright green, sometimes shaded with brown tinged with yellow ; 

 drying darker. 



The above description is made from the typical form only ; this 



branches out into so many states, some of which look so like distinct 



species from the type, that it would be impossible to describe them 



all under one specific character. The typical form is figured in 



Plate 317, and one of the most divergent forms in Plate 318 ; 



these plates will give a fair idea of the extremely different facies 



assumed by some of these forms. I am unable to call them true 



varieties because, after having carefully watched them for four years 



at all seasons, and under varying conditions, they all revert more 



or less closely to the type, on shoots produced from the same root- 

 stocks ! 



P. graminifolius grows abundantly in Pidley Fen, Huntingdon- 

 shire, over an area of about two square miles. As a native of our 

 islands, it seems hitherto to have escaped the notice of British 

 botanists, although it probably grows in other English localities, 

 and certainly ought to occur in the more northern counties of 

 Scotland. However this may be, with one or two exceptions after- 

 wards referred to, I have not met with any specimens in collections 

 of British plants, hitherto examined, which can be assigned to this 

 form ; nor does it seem to be included in specific descriptions of P. 



heterophijllus by British authors. 



Journal of Botany.— Vol. 30. [Feb. 1892.] » 



