82 



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



Fig. 31 A—C, P. polygonus Ch. & Schl. 

 A, Transverse section of leaf below the 

 middle, \f^, showing the lacnnar system (/) 

 and the bast-bnndles; str^ marginal strand; 

 ?/(, «', nerves (vascular bundles); B, Pistil; 

 a, lateral view, h, ventral view, ^^', C, Trans- 

 verse section of the central axis of the stem, 

 showing the bundles and their channels, 

 ^0. ^ D—F, P, Ulei ScHuar. D, Transverse 

 section of stem, showing the arrangement 

 of the lacunar system, the subepidermal 

 strands {str\ and the vascular bundles of 

 the central cylinder {cc)^ X occasionally 

 occurring interlacunar bundle, 'Y > ^. Top 

 of a stem-leaf, ^ ; F, Transverse section of 

 this leaf, at the middle, vi, n', sir, as in 



are either quite wanting or present 

 in a very slight number. The 

 crosscut-form of the central stele 

 is rhomboid, which results from 

 the median bundles running more 

 separately than in general and 

 the latera,! ones being considerably 

 reduced both in number and size, 

 the stele thus presenting a four- 

 bundled diagram. The leaves taper 

 more abruptly into an apex, less 

 acute by far than in P. polygonus. 

 The leaf is through its whole width and up to the very 

 top intersected or replenished with harrow channels, the 

 crosswalls of which are rather approximate, which 

 makes it appear reticulate under the lens. Two vascular 

 bundles run on either side of the main-rib and, between 

 them, thin bast-bundles nearly as in the foregoing species, 

 but the border-strand is considerably weaker. Ligules 

 more durable, their front-field is 12 — 15 (17)-fibrous. 



It should be observed, that my researches are made 

 on young shoots from a creeping rhizome, the only 

 materials hitherto accessible to me. Spike-bearing indivi- 

 duals may have the interlacunar sclerenchyma (the ligu- 

 lar bundles) a little more developed. 



The species is figured in Graebner, Potamog. ap. 

 Engler, Pflanzenreich IV, 11, 1907, 105, f. 25 A (habit- 

 figure); B, fruit, seems to me to be a polygonus-huit, 

 cfr. Schumann, fruit 1,5 mm long etc. 1. c! 



Distribution. Brazil, Pro v. Rio de Janeiro, Serra 

 do Itatiaia, 2,460 m. s. m., 02, Dusen (lib. Stockholm.). 

 — Leg. Glaziou, N. 6721; det. Schum. (hb. Haun.). 



Subsectio 11. Oxyphylll Hagstr. 



Caulis ± compress us internodiis elongatis, nodis 



biglandulosis. Folia linearia multinervia acuta vel acute 



cuspidata basi ± rotundata. Ligulce fissse, multinerviae, 



apice rotundatae. Pistillum stylo brevi stigmate parvo. 



' Fructus OYOxAei leviter compressi (P. oxypliyll.). 



This group occupies an intermediate position between the Polygoni and the 



Pusilli. It is like the latter as regards the styles and stigmas, but differs by the 



