33 



NOTES ON PONDWEEDS. 

 y By Alfred Fryer. 



Potamogeton varians Morong in Herb. ined. — Stem springing 

 from a tuberous rootstock, slender, usually simple below, with a few 

 branches above the middle, not divided into secondary branchlets ; 

 or in shallow water with a few branches fi'om the base, each 

 springing from the axil of a persistent leaf, and then rarely with 

 very short secondary branchlets. Leaves varying from narrowly 

 Imear-lanceolate membranous, to oblong obovate spathulate or 

 orbicular coriaceous. Lowest submerged leaves reduced to phyllodes, 

 or narrowly linear-lanceolate, bodkin-pointed ; ordinary submerged 

 leaves sessile or stalked, narrowly lanceolate, attenuated towards 

 each end, or spatlmlate oblong, or obtuse mucronate, fiat and 

 ascending, or rarely folded and recurved. Floating leaves alternate, 

 obovate, oblong, spathulate or orbicular, coriaceous, rarely membranous, 

 long-stalked, belonging to the barren state of the j^Zan^, and never 

 du'ectly sustaining the flower-spike. Stipules narrow, slender, 

 herbaceous, persistent, blunt, or contracted into a short mucro when 

 dry, not becoming greatly enlarged on the upper part of the stem, 

 nor cymbiform, to support the inflorescence. Peduncles lateral, not 

 necessarily subtended by opposite coriaceous leaves, but usually 

 springing from the stem opj^osite a membranous leaf, resembling the 

 submerged leaves in shape and structure, or rarely opposite a stipule 

 only, very rarely opposite a coriaceous leaf; slightly thicker than 

 the stem, not swollen upwards, as long as the oi^posite leaf : 2-8 in. 

 Fruiting- spike |-1 in. long, rather slender, not dense; drupelets 

 small, flattened and impressed at the sides, nearly circular in outline, 

 with a short subcentral beak; central keel acute, almost n-inged; 

 lateral ridges prominent. Colour of the whole plant, reddish green, 

 or light green, drying darker ; the lower part of the stem and young 

 shoots sometimes bright red. 



P. varians is a plant of diffuse growth, usually but little branched, 

 with slender stems from 6 to 18 in. long. It has few permanently 

 submerged branches, the mass of vegetation ultimately rising and 

 floating on or near the surface of the water. When growing in 

 shallow, reedy ditches, its upper branches are often lilted out of 

 water, and continue to grow in the air. It is also remarkable for 

 its ability to grow, when forsaken by the water, on the grassy 

 bottoms of ditches as dry as an ordinary meadow. Under these 

 conditions it forms little tufts of leaves in the axil of each stipule 

 along the stem, which continue to grow fully exposed to the air and 

 sunshine. The already-formed submerged leaves on the branches 

 that grow under water do not die, but become coriaceous, so as to 

 better withstand the effects of heat and drought. Some of the 

 leaves produced under these circumstances are remarkable for being 

 membranous and transparent, like those of P. ^jiZrt?jf«</t;/e2(s grown 

 under like conditions. The true land-form also is freely produced, and 

 enables the rootstock to swell into moniliform tubers, or these are at 

 times produced directly from stolons thrown out by the land-form. 



Journal of Botany. — Vol. 27. [Feb., 1889.] d 



