56 



J. O. HAGSTBOM, CEITICAL EESEAECHES ON THE POTAMOGETONS. 



P. Maackiaiius Ar. Bennet. 



Notes on Potamogeton, — in The Journ. of Bot. 1904, 74. — P. serrulatus 

 Regel et Maack, in Kegel, Tent. Fl. Ussur. 1861, 153. — P. Rohhinsii Oakes var. 

 ja'ponicus Ar. Bbnn. Notes on Japan. Potamog. in Bull, de I'Herbier Boiss. 1896, 

 546, 549. - Fig. 20, D, E, F. 



Dr. P. Graebner in his Potamogeton monograph (1907 p. 108) says, »Af- 



finitas speciei mihi valde dubia est ; 

 probabiliter melius subsectionem 

 propriam constituit; ex cl. A. Ben- 

 nett in litt. melius prope P. Roh- 

 hinsii ponenda est.» Nevertheless 

 he puts it near to P. ohtusifoliiis 

 M. & K. The opinion of Ar. Ben- 

 nett, however, is quite correct, 

 since the species presents the most 

 obvious resemblance to P. Rohhinsii, 

 both morphologically and anatomi- 

 cally. To the above stated com- 

 mon characters we add: The ana- 

 tomical diagram of the stem is the 

 same, except that the interlacunar 

 strands are absent and the lateral 

 groups of bundles in the stele more 

 reduced. But the endodermis is 

 entirely alike in both species. In 

 the peduncle P. Maackianus has a 

 circle of subepidermal strands and 

 besides more vascular- and bast- 

 bundles (fig. 20, F). On the con- 

 trary, the number of the schleren- 

 chymatous strands of the leaf is 

 considerably limited. To the mor- 

 phologic differences belongs, among 

 others, that the leaves are of the same width throughout their whole length, the top 

 abruptly cuspidate forming a broad, obtuse apex, the denticulation abating towards 

 the base, that the stem is compressed but scarcely bicanaliculate, the cross-cut form 

 of the indunde oval or oblong etc. Fruit seldom seen. 



Distribution. Japan, Hakone. Siebold it. sec. 1859 — 63 (hb. Stockholm.). 

 The species obviously has its distribution area in East-Asia: Japan, Corea and adja- 

 cent districts, thus constituting, by its near affinity with the foregoing species, an 

 interesting combining link of the floras of both sides of the Pacific. 



Fig. 20, A, B, C, P. Rublinsii Oakes, A, Leaf, X 2,5; £, Top of a leaf, 

 -y*; C Transverse section of peduncle, showing the shape and the dispo- 

 sition of the bundles, 'if. — D, E, F, P. Maackianus Bess. Z), Leaf, X 2,5; 

 E, Top of a leaf, y; E, Cross section of peduncle, showing the subepi- 

 dermal strands (str) and lacunar bundles (hatched), ^^; 7n, 71' , 11", ski = 

 Fig. 19. 



