214 J. O HAOSTRÖM, CR1TICAL RESEARCHES ON THE POTAMOGETONS. 



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

 minens. 



f. co ni mun is Hagstr.: Folia caulina minora angustiora 60—100 X 10—20 mm ± 

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

 103, C. 



This form includes all crosses of validus-type without f loating 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 verv much to P. gramineus f. jemt- 

 landicus which, however, has longer internodes and quite sessile leaves as ever}^ true 

 gramineus-foim. 



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

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

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

 leaves, usually appearing in shallow water. The smallest form is >P. lucens f. ter rest- 

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



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

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

 elongatus, 20 — 30 cm. 



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

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

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



As in all Zizii-iorms, the branch-leaves are also here considerably less than in 

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

 except sometimes the involucral leaves (influence from P. granlin.). 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-iorms. 



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

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



This form comprehends P. lucens f\ longi pcdunculalus Tis., 1. c, no. 64 as well 

 as b 8plendidi88imu8 Tis., 1. c, no. 66 (P. Zizii subv. Tiselii Graebner, Potamog. 

 1007, 82) between which no real difference is to be found. 



f. pulcherrimna n. f. — P. lucens v longi pctiolatus Tis., 1. c, no. 144, non no. 

 00: — Folia auperiora ± longe petiolata, ceterura ut praoedens. 



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

 the upper stem-leaves and from f. longipetiolatUS by ils longer upper stem-internodes 

 and not quite BO long petioles. 



Distribution of /'. Zizii M. & l\. Sweden, in lakes eto. looally among the 

 parents, from Scania bo the aorthern limit of /'. lucens in Medelpad and J emiland. 



