POTAMOGETO> T IN THE EXGLISH LAKES 161 



as a variety of it. It differs from it, however, in many essential 

 features. P. pusillus under favourable conditions produces copious 

 distichous branches in the upper part, assuming a bush-like habit, 

 but the branching of P. panormitanus is mainly from the base, and 

 any necessary prolongation is attained by the lengthening of the 

 upper internodes rather than by multiplication of branches. The 

 spike-bearing branches of P. pusillus are relatively long, those of 

 P. panormitanus short. The leaves of the former are darker in 

 colour — dull green or brownish — softer in texture and normally with 

 a sub-obtuse apex. Those of the latter are Tighter (or yellowish) 

 green, much stiffer, with a more prominent midrib (which, however, 

 lacks the characteristic 1 or 2 rows of lacunae of pusillus ) and 

 a longer, more acute apex. Even more diagnostic are the stipules 

 and turios. In P. pusillus the stipules (ligules of Hagstrom) are 

 always open and convolute, but in P. panormitamts they are connate 

 for quite two-thirds to three-fourths of their length. The turios of 

 the former are larger, more swollen, in the middle, and developed best 

 in the branch-tops, while those of the latter are smaller (12-15 mm.), 

 more slender and produced at the base of the stem or branches. 

 Hagstrom (p. 102) says "very rarely there are turios on the 

 rhizomes." We have seen them in that position on Lake District 

 specimens of this species, but never thus in P. pusillus. P. panor- 

 mitanus nourishes here only in Esthwaite Lake on the finest and richest 

 soils — whereas pusillus and lacustris are rather more cosmopolitan in 

 in this respect — under a light-intensity of 10 % or less, and these 

 conditions may possibly be universal. 



Of herbarium specimens we have seen, many of those labelled 

 P. pusillus or P. trichoides, and all those under P. pusillus var. 

 tenuissimus are this species. 



P. panormitanus does not appear to vary much under the different 

 light conditions in which it has been found. In this respect it differs 

 markedly from P. ohtusifolius and P. pusillus. 



P. obtusieoltus Mevtens et Koch in Holding Deutschlands 

 Flora, 855 (1823); Cham, et Schl. in Linncea, ii. 178 (1827); 

 Fries, Novit. Flor. Suec. ed. 2, 47 (1828) ; Koch, Syn. PI. Germ. 

 et Helv. ed. 2, ii. 780 (1841) ; Beichenbach, Icon. Flor. Germ. vii. 

 16 (1845) ; Syme, Eng. Bot. ed. 3, ix. 47 (1869) ; Hooker, Stud. 

 Fl. ed. 3, 435 (1884) ; Bab. Man. ed. 9, 442 (1904) ; Morong, 

 Naiad. N. Amer. 40 (1893) ; Asch. et Graebn. Synop. Flor. Mitteleur. 

 ed. 2, 521 (1913). P. f/ramineus Smith, Eng. Fl. ed. 2, i. 235 

 (1828). P. compressus Both, Tent. Fl. Germ. i. 73 (1788). 



Stem normally much branched, slender, compressed. Leaves 

 sessile, narrowed below, very slightly tapering at the apex, obtuse or 

 rarely subacute, mucronate. Usually 3-nerved, but we have leaves 

 from ponds on Colthouse Heights with 5 nerves ; Syme (I. c.) savs 

 he has never seen such ; Koch gives 3-5, while Fieber, Pot. Bohi'n. 

 1838, figures 7. Length variable, about 7 - 5 cm. x 2 mm. in Esth- 

 waite, but showing the same tendency as P. pusillus to elongation in 

 deep water. Stipules open, very obtuse, unequal in length, about 

 15-20 mm. Peduncles very short as a rule — about 8 mm.— but in 

 Hawes Water, Silverdale, 36 mm. Fruits normally larger (3'0- 



