KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 55- NIO 5. 



115 



bundles. Inside this stratum there is a circle of large-roomed lacunse. Central stele 

 compressed and its bundles arranged according to the oblong stele diagram in three 

 groups with three X3dem portions. 



The stem-leaves are provided with sclerenchymatous strands in the lacunar 

 part but the marginal strand is thin and there is no tendency 

 to form bast-bundles like those characteristic to the Compressi. 

 The leaves are 3 — 5-nerved and not at all digressing from the 

 pusillus-tyjie as to the nervation. »The closely packed veins» 

 are the side-walls of the lacunar and »the cross veins» are their 

 cross-walls. The lacunae do not occupy the whole space between 

 the midrib and the lateral nerves in the upper half of the leaf. 

 (See the figure!) 



A plant labelled »Raikie's Niger Expedition 1857 — 59. 

 Nupe. Coll. C. B arter» (hb. Stockholm.) lacking f loating leaves 

 in the spike-region and resembling P. Preussii as well as P. java- 

 nicus might be of a hybrid origin. The stigmas are very small, 

 by far not covering the upper surface of the style. Leaves as 

 in P. javanicus. Ligules fevv-nerved in the front-field. Pollen 

 small-grained, well-shaped. No fruit seen. 



Subseries b. Obtusi Hagstr. 



The boundary-line between these two subseries is not very 

 marked. Some forms of P. pusillus have obviously tapering leaves 

 and the leaves of P. obtusifolius have a lacunar system with 

 subepidermal strands (see the figs.) and I have said above that 

 the P. Asch. f. pusilloides m. has pretty soft and flexible leaves; 

 however, this arrangement can ad interim serve the purpose to 

 give a survey of the species belonging hereto, until better know- 

 ledge is obtained as to the pistils and fruits. 



ö i Fig. 50. V. Preussii Benn. 



A, Top of a stem-leaf, \°. 



B, Transverse section of a 

 stem-leaf at the middle, m, 

 midvcin, »', n 2 , lateral veins. 

 str, scler. strands, \° . C, 

 Transverse section of stem, cc, 

 stele, ep-hp, epidermis and its 

 strengthening Iayer. 1 - 1 °. The 

 Preussian material of Kameran 

 employed for the drawings! 



P. obtusifolius Mertens & Koch. 



In Röhling, Deutschlands Flora, 1823, 855. — P. com 

 pressus Roth, Tent. Fl. Germ. I, 1788, 73; Wallman ap. Lilje 

 blad, Utkast till en sv. fl., ed. 3, 1816, 706; Wahlenberg, Fl. upsaliensis, 1820, 

 59. — P. tataricus Lessing in Linnaea IX, 1834, 206. — P. angustatus et P. Lilje- 

 bladii Wallman ap. Reichenb., Icones fl. germ. VII, 1845, 16. — Fig. 1, F, 24, D, 51. 



The stem has the usual compressed form. The longitudinal axis is a little 

 more than twice the shorter one, on one or both sides slightly furrowed. Its ana- 



