.44 



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



farther to the north, for instance at Nikandrowsky ostrov, 70° 20' n. L. (coll. Lund- 

 STROM, 75, Arnell, 76, hb. Stockholm.). From this boundary it spreads southwards 

 through all parts of the world, its distribution consequently being universal and sur- 

 passing all the other species of the genus. 



It is evident that a species, appearing under so different climatic conditions, 

 arctically (see above!) and equatorially (for instance in the Albert Edward Lake, 



Africa, coll. R. E. Fries, 1912, 



^ ~ ^ — ^ hb. Upps.), and occurring both 



in salt and fresh water, at the 

 shores of the sea and in small 

 lakes, in rivers and rivulets, 

 on muddy, fat ground and bar- 

 ren, sandy, clay bottom, must, 

 of course, be met with in many 

 different varieties or forms. 

 Thus we find forms with horse- 

 hair-like stems and leaves and, 

 again, stems 2 mm in diame- 

 ter at the base and with 5 mm 

 broad stem-leaves and number- 

 less transition forms between 

 those extremities; with short 

 and long sheaths (at most 50 

 mm) ; wdth large (4,5 x 3 mm) 

 and smaller (3x2 mm) fruits 

 (megacarp and microcarp forms). 

 Of all the variations of this 

 species I have observed, none 

 seems to be more significant or 

 of a greater systematic value 

 than the different forms of the 

 leaf-apex, of which the figure 

 beside should give an idea. The 

 body of the forms should be 

 divided into the two varieties established here below, according as their leaf-apex is 

 endowed with a conspicuous mucro or more slowly tapered. 



The somewhat peculiar v. mongolicus A. Benn. ought to be kept, and likewise 

 the P. zosteraceus Fries and P. striatus R. & P. All the other innumerable varia- 

 tions should after my opinion be considered only as rather accidental and insignifi- 

 cant forms of inferior value. 



The following arrangement of the forms of P. pedinatus is only an attempt 

 to put in order the great multitude of forms which I have had an opportunity 

 to examine. 



Fig. 18. P. pedinatus L. Different forms of tiie leaf-apex. A^ B, C, D, 

 Tar. diffusus m. \^. E, F, G, var. nngulatiis m. '/. H, var. striatus (E. & P), J. 

 K, Middle portion of H, showing the nerves and lacunjc, ^-•, L, var. diffusus, 

 m. \^. A, basal stem-leaf, B, from the middle of the stem, C, involucral leaf, 

 D, branch-leaf; E, leaf from the midde of the stem, F, involucral leaf, G, basal 

 leaf of a short branch; H, top of a stem-leaf, material from Jnjuy, South Ame- 

 rica. A", Middle portion of this leaf showing the position of vascular bundles, 

 strands and lacunar walls, cf. fig. 16, F! L, top of a basal stemleaf with the 

 position of nerves and lacunee visible. 



