KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 55. N:0 5. 57 



P. Maackianus is said to hybridize with P. compressus (Graebnee, Potamog., 

 1907, 165), but I have not seen the plant referred to (Faueie, Japanese pL 10370), 

 and with P. malaianus Miq. (Ar. Bennett, Philippine Journ., 1914, 342) in the 

 Lake Lanao, Mindanao, 1906, leg. Mary Strong Clemens. On a sheet of this plant 

 preserved in Copenhagen (Bot. Mus. University), two forms are present : 1 ) P. nippo- 

 nicus Mak. and 2) The new form named P. philippinensis Ar. Benn. The stem of 

 this plant is terete and the anatomical diagram of it is: epid. + one-layered pseu- 

 dohyp. + subepid. str. + ligular str. + 0-0-end. + CC of eight-bundled type. Leaves 

 serrulate lance-linear, 65 X 5—6 mm, with a protracted malaianus-like, sharp cusp, 

 base sessile, sheathing like P. Maachianus, the longitudinal 4 — 6 lateral nerves runn- 

 ing like those of P. mal., but the cross-veins not so densely placed as in this one. 

 Besides, the thin, longitudinally interjacent, mechanical strands of P. Maachianus 

 are absent. — The author seems to have confounded these two forms when writing: 



— Lower leaves 8 to 15 mm. wide. etc. It is the narrow-leaved form that 



ought to bear the new name. 



Sectio IV. Axillares Hagstr. 



Caulis compressus ± bicanaliculatus vel subteres — teres. Folia sessilia vel ± pe- 

 tiolata, serrata — serrulata — integerrima, ligulata, ligulis in ochream fissam vel ra- 

 rius integram connatis. Prcefoliatio adplicata (subsect. 6 — 13), involuta (subsect. 14 

 — 23) vel convoluta (subsect. 24 — 25). Hyhernacula rhizomatica vel caulina. 



To this section belongs the bulk of the Potamogetons and it is evident, that 

 the evolution of the genus has gone this way. We take the youngest types to be 

 the forms with involute prsefoliation with a few exceptions having floating leaves. 

 These species derive their origin partly from the submerged narrow-leaved, partly 

 from the submerged broad-leaved forms, between which the difference is not very 

 prominent indeed. In this section hybridization is rather common, bj' which the 

 evolution may be said to be in process. 



Subsectio 6. Crispl Wallman. 



In LiLJEBLAD, Utkast till en svensk Flora 1816, 706. — Batrachoseris Irmisch, 

 t)ber einige Arten etc. 1858, 17. 



Caulis compressus bicanaliculatus. Folia late linearia serrata. Ligulce emar- 

 ginatse. Pistillum stylo conspicuo, stigmate ovali oblique affixo. Fnictus ± longe 

 rostratus. 



This group is richly provided with both rhizomes and cauline propagating buds. 

 Only one species is known. P. Chamissoi Ar. Benn. must be ranked under the 

 Lucentes. 



K. Sv. Vet. Akad. Handl. Band 55. N:o 5. 8 



