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



however, proved to be the hybrid P. nodosus Poir. x Richardson i i Rydb., and I 

 therefore have chosen a new name for the above hybrid. 



P. alpinas Balb. x perfoliatus L. (P. prussicus Hagström, New Potamoge- 



tons, in Bot, Not, 1908, 103—106). 



This bastard nas 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 niore 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 innch slighter dentieulation and 

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

 strands and in an endodermis of O-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 



p. alpinifolius Hagstr. 1. c. 



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

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

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



P. alpinus Balb. x polygonifolius Pourr. (P. spathulatus Schrader ap. 

 Kocn et Ziz, Catalogus plantarum Pålat., 1814, 5, 18. ■ P. Kochii ScHULTZ, Archi- 

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



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

 approaching to P. alpinus, and ser. Curtii verging to P. polygonifolius, yet 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 bnt with a 

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



p. SVecicilS 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 Bloping bases. Apex obtuse as in 

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

 be said to be intermediate. 



Distribution. Siveden, Scania, Broby in Helgeå, 57, Scheutz (hl>. Upps.) 

 ex hb. K. F&IBS, who has written on the label : »Est P. rufcsrens* ; the same 

 station, (>f>, THBDENIUS (hb. CJppe.) J S. ALMQUI8T lias noted of this: ;'ir icke poty- 

 gonifoUu8, möjl. dess hybrid med rufescens* ( Possibly polygonif. < rufesc.). — 

 Oermany, Rhein-Pfalz, Kaiserslantern, A. Bbauh (hb. Lund.), 4.'{. Sohultz (hb. 

 Stockholm, (^t Uppsal.). — More stations hitherto not known; misreported from 

 Norway by Gbaebneb in Potamog., 1907, \'V.\. 



