128 J. O. HAGSTROM, CRITICAL RESEARCHES ON THE POTAMOGETOKS. 



apice rotundatse, in spatio intercarinali 7 — 8 nerviae, ca. 12 mm longse, biglandulosse. 

 Spica ignota. 



Anatomy coincides nearly with that of P. pusillus except that the leaves, in 

 their upper half and sometimes also farther down, are lacking the lacunar rows along 

 the midrib, and on either side of it always are furnished with very thin, mechanical 

 strands scarcely perceivable to the naked eye. The topography of the central axis 

 of the stem is of the circular type, and for the rest of piisillus-structnTe. 



This species constitutes an interesting combining link between the Oxyphylli 

 (P. suhsibiricus) and PnsilU {P. pusillus) and would be ranked together with the 

 former almost with the same right as with the latter. Ligules and leaf-apexes, how- 

 ever, unite it with the Pusilli. 



Distrihiition: Greenland, probably endemic. It is gathered at Ivigtut (83, 

 Berlin), Christianshab (90, Hartz), Jakobshavn (92, Sorensen), Kingua Orpiksnit, 

 68° 30" N. L. (90, Hartz), Ritenbenk, 69° 44" (88, Hansen) and at Sarkak, W N. L. 

 (90, Hartz). The materials are preserved in Hb. Univ. Copenhagen. 



Subsectio 14. Javanici Graebner, in A. Engler, Das Pflanzenreich IV, 11, 



Potamog. 1907, 45. 



Caulis teres vel rarius subcompressus, ramosus. Folia semper biformia: vere 

 natantia brevipetiolata, paucinervia; submersa anguste linearia paucinervia in apicem 

 acutum sensim attenuata, secundum costam mediam ssepe valde lacunosa. Ligulce 

 typice fissse, in spatio medio paucinervise. Stylus conspicuus vel subelongatus. Fruc- 

 tus carinatus saepe rugosus vel muricatus. 



Morphologically as well as anatomically and biologically (the turios!) this group 

 most closely associates to the species of the pusilloids which have subcoriaceous in- 

 volucral leaves, but exhibits also affinity with the natans-group, to which P. Vaseyi 

 can be said to form the transition by its characteristic submersed leaves. 



The coriaceous leaves exhibit the simplest structure with small air-cells in the 

 upper surface, a little larger in the lower surface and, typically, between those a 

 one-celled layer, separating the upper and the lower lacunae from each other. Upper 

 surface endowed with stomata. 



As far as known to the writer the ligules are open and convolute except in 

 the new species P. subjavanicus m. in which they are connate at the base. 



As to the fruit the group presents resemblance to the Compressi, Monogyni and 

 Muricati. 



The stem anatomy of the Javanici differs from that of the Pusilli by being typic- 

 ally endowed with a pseudo-hypoderma and by the cross-cut form of their central axis 

 being mostly rounded. In other words the anatomical conditions are more uniform 

 than in the group next before. But exceptions occur also here. 



