1(52 THE JOURNATi OF HOT INT 



3*5 mm.) than in pusillus or mucronatus (Fries//), but occasionally 

 only 25 mm. long and then similar to those of pusillus. Fruiting 

 more freely than any other linear-leaved species and in Esthwaite 

 readily propagating by large winter-buds also. It is the only species 

 of Potamogeton in this district frequently producing fertile fruit under 

 water. This species occurs in Windermere, Esthwaite, Hawes Water, 

 and Grasmere, upon more fertile soils than either pusillus or lacustris. 

 In Esthwaite and Hawes Water it is found under a light-intensity of 

 10% or less. 



Potamogeton pusillus L. Sp. PI. 127 (1753) ; Fries, Novit. 

 Elor. Suae. ed. 2, 48 (1828); Fieber, Pot. Bohra. 39 (1838) ; Koch, 

 Synop. Fl. Germ, et Helv. ed. 2, ii. 780 (1844); Svine, Eng. Bot. 

 ed. 3, ix. 49, tab. 1419 (1869) ; Hooker, Stud. Fl. ed. 3, 435 (1884 ) ; 

 Morong, Naiad. N. Amer. 45 (1893) ; Bab. Man. ed. 9, 442 (1904) ; 

 Asch. et Graebn. Synop. Fl. Mitteleur. ed. 2, 525 (1913). 



Stem nearly cylindrical, very slightly compressed; often much 

 branched in the upper part, at times nearly simple. Leaves narrowly 

 linear, very variable in length with a marked tendency to elongation 

 in deeper water. 



(a) Deep-water forms with long and narrow leaves about 50- 

 70 mm. x0 - 8-l*0 mm., narrowed below and gradually tapering to an 

 acute tip (cf. Crummock). 



(b) Intermediate forms (typical) with leaves normally about 

 30-45 mm. X l'O mm., with tips more or less rounded and sub-acute. 

 (Pond form, cf. Mouzell, Green Hauhne.) 



(c) Shallow-water and high light-intensity forms with short 

 obtuse leaves less than 30 mm. long and 1*4-1 '8 mm. broad; darker 

 and thicker in texture than («) or (b) (cf. High Dam). 



All submerged leaves soft and flexible, obtuse, sub-obtuse or acute, 

 3-nerved with 1 or 2 rows of lacunae on either side the midrib. 

 Lateral nerves very near the margin. Ligules small, obtuse, always 

 open and convolute. Peduncles slender, very variable in length. 

 Fruit small (2'0-2'5 mm.), not smooth, normally broad below. 



This species is found in the English lakes upon the coarser and 

 only moderately fertile soils (ef. lacustris) under a light-intensity of 

 9Q_y°/ o . The two types — pusillus and lacustris — remain distinct 

 where their light-intensity conditions overlap, as in Crummock. 



The leaves vary in colour from light green to dull olive-green. 

 In Klingksieck and Valette's Code des Couleurs (Paris, 1908) these 

 colours are numbered respectively 282 and 238 — as viewed against 

 white paper. In older leaves the colour may be tinged with brown 

 (No. 232, K. & V.). The colour of P. panormitanus varies between 

 Nos. 276-278 (K. & V.). 



Normally the leaves are between 20-40 mm. in length, and rarely 

 over 1 mm. in width. The extreme length that has been observed is 

 70 mm. (Crummock W.), and the extreme width 1*8 mm. (High 

 Dam). A characteristic feature of the leaves is that they gradually 

 taper toward the apex and are narrowed below — very long leaves 

 appearing subpetiolate. The involucral leaves have very prominent 

 air lacuna? and are considered to represent primitive floating leaves. 



As shown above, P. pusillus exhibits distinct variations in rela- 



