214 J. O HAGSTROM, CRITICAL RESEARCHES ON THE POTAMOGETONS. 



the upper part of the stem, nevertheless, show an evident influence from P. gra- 

 mineus. 



f. communis Hagstr.: Folia caulina minora angustiora 60—100 X 10—20 mm ± 

 conspicue petiolata. Ligalse sat persistentes. Pedunculus ± 100 mm longus. Fig. 

 103, C. 



This form includes all crosses of validus-type without floating leaves proper, 

 with more or less small and narrow, more or less evidently short-petioled stem-leaves, 

 rather long persistent stipules, 20 — 40 mm long, and peduncles of middling length. 

 The small differences occurring here, are not of the importance to deserve own names. 

 Part of hereto belonging crosses approaches very much to P. gramineus f. jemt- 

 landicus which, however, has longer internodes and quite sessile leaves as every true 

 gramineus-f ovm. 



f. coriaceus (Meet, et Koch). P. lucens 3 coriaceus M. & K., Deutsch. Fl. 1823, 

 850. — P. coriaceus Fryer, Notes on Pondw. in Journ. of Bot. 1889, 8 — 10: — All 

 forms of validus-tyTpe (short internodes, see above) with conspicuously coriaceous 

 leaves, usually appearing in shallow water. The smallest form is ^P. lucens i. terrest- 

 ris Tis.» in Tiselius, 1. c, nos. 66 — 67. 



Var. ,3 elongatus (Fieber) Reichenb., Icones VII. 1845, 24, t. XXXIX, f. 

 68: — Internodia omnia producta (10 cm et ultra). Pedunculus ut plurimum etiam 

 elongatus, 20—30 cm. 



f. foliosus (Tis.). P. lucens C joliosus Tis. 1. c. no. 63: — Folia caulina magna, 

 fere ut in P. lucenie, ramea minora (effectu P. graminei) omnia sessilia v. subsessi- 

 lia; folia floralia interdum breviter petiolata. Ligidce ad P. gramineum vergentes. 



As in all Zizii-ioxvL\s, the branch-leaves are also here considerably less than in 

 P. lucens, though the stem-leaves are very large and lucens-V^ke; all nearly sessile 

 except sometimes the involucral leaves (influence from P. gramin.). Ligules verging 

 towards P. gramineus, consequently more or less deciduous (less durable than in 

 P. lucens). 



The short branches below the primary spike are frequently branched again by 

 branches of the second rank, hence the name foliosus. This mode of branching is 

 inherited from P. gramineus and characteristic of many Zizii-iovn\&. 



f. longipeduiiculatus (Tis.): — Folia caulina angustiora (80— 140 X 18 — 19 mm), 

 suprema ± conspicue petiolata. Pedunculus longissimus, 20 — 40 cm. 



This form comprehends P. lucens -q longipedunculaius Tis., 1. c, no. 64 as well 

 as d- splendidissimus Tis., 1. c, no. 65 (P. Zizii subv. Tiselii Graebner, Potamog. 

 1907, 82) between which no real difference is to be found. 



f. imlclierrimus n. f. — P. lucens '( longipetiolatus Tis., I. c, no. 144, non no. 

 60: — Folia swperiora ± longe petiolata, ceterum ut praecedens. 



This form differs from the form next before only through the longer petioles of 

 the upper stem-leaves and from f. longipetiolatus by its longer upper stem-internodes 

 and not quite so long petioles. 



Distribution of P. Zizii M. & K. Sweden, in lakes etc. locally among" the 

 parents, from Scania to the northern limit of P. lucens in Medelpad and Jemtland. 



