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



however, proved to be the hybrid P. nodosus PoiR. X Richardsonii Rydb., and I 

 therefore have chosen a new name for the above hybrid. 



P. alpinus Bale, x l)erfoliatuS L. (P. pruSSiCllS Hagstrom, New Potamoge- 

 tons, in Bot. Not. 1908, 103—106). 



This bastard has been collected only in Germany and Norway. It is easy to di- 

 stinguish from P. alpinus by the leaf-serrulation (to be studied on young, unhurt 

 leaves), from P. perfoliatus by the ligules more or less verging to those of P. alpi- 

 nus and by the leaf-bases, from P. nitens (i. e. P. gramineus X perfoliatus), which it 

 extremely resembles, by the obtuse leaves, the much slighter denticulation and 

 by the anatomical conditions of the stem consisting in the absence of cortical 

 strands and in an endodermis of 0-cells. 



According as the leaf-form corresponds more with the one or the other of the 

 parent-species the different forms are referable to the two varieties: 



a. abbreviatus Hagstr. 1. c, or 



|3. alpinifolius Hagstr. 1. c. 



To the former var. I have reckoned the form of Darkehmen, East-Prussia, f. 

 darTcehmensis Hagstr. 1. c. ; and to the latter f. pelplinensis Hagstr. 1. c, from Pelplin, 

 West-Prussia. — Norway Romerige: Raumaelv and Ostenso, Blytt (hb. Christ.). 



P. alpinus Balb. x polygoiiifoliiis Pourr. (P. spatlmlatus Schrader ap. 

 Koch et Ziz, Catalogus plantarum Palat., 1814, 5, 18. — P. Kochii Schultz, Archi- 

 ves de la Flore de France et d'Allem., 1842, 72). 



Fischer has diveded the forms of this hybrid into two series: ser. Kochii, 

 approaching to P. alpinus, and ser. Curtii verging to P. polygonifolius, j^et without 

 a closer explanation of the similitudes or differences. All the Palatine specimens I 

 have seen are like P. polygonifolius in that respect that the lower leaves are petioled. 

 This form I propose to name: 



a. palatinensis n. f. — Foliis inferioribus petiolatis. 



Our Scanian form, on the contrary, has the lower leaves sessile but with a 

 narrow stalk-like base. This form may be called : 



p. svecicus n. f. — Foliis inferioribus sessilibus. 



The upper leaves of both forms are long-petioled with petioles as long or 

 longer (rarely shorter) than the blades with their sloping bases. Apex obtuse as in 

 P. alpinus. The stem-anatomy shows influence from both the parent-species and can 

 be said to be intermediate. 



Distribution. Sweden, Scania, Broby in Helgea, 57, Scheutz (hb. Upps.) 

 ex hb. E. Fries, who has written on the label: »Est P. riifescens» ; the same 

 station, 65, Thedenius (hb. Upps.); S. Almquist has noted of this: »ar icke poly- 

 gonifolius, mojl. dess hybrid med rufescens» (= Possibly polygonif. X rufesc). — 

 Germany, Rhein-Pfalz, Kaiserslautern, A. Braxjn (hb. Lund.), 43, Schultz (hb. 

 Stockholm, et Uppsal.). — More stations hitherto not known; misreported from 

 Norway by Grabbner in Potamog., 1907, 133. 



