KUNGL. SV. VET. AKADBMIENS HANDLINGAE. BAND 55. N:0 5. 



133 



subepidermal strands pretty feeble, otherwise as in the pusilloids. Beneath the pri- 

 mary spike the central stele is nearly terete with a rounded crosscut-form, the bun- 

 dles indistinctly separated or quite fused with a single central cavity. The stele of 

 the stem-prolongation, again, has rather oval crosscut-form and the lateral bundles 

 distinctly separated from the median ones by mechanical tissue. The hypoderma of 

 the stem-prolongation often 2-layered to stiffen that spike-bearing organ. 



The lacunar system of the submersed leaves typically provided with subepi- 

 dermal strands in the lower surface (fig. 58, 

 G, str.) or sometimes lacking them (specimens 



from Madagascar and Kunene), in which case ~\^d^^TYVi~^ryY^X'\y~<tr^^^^ /|1 A 

 the leaves become more flexible. 



These small anatomical differences toge- 

 ther with the different mode of prolonging 

 the stem, dichotomously or cincinnately, might 

 suggest other discrepancies not yet sufficiently 

 attended to. 



Distribution. Asia, Khasia Ind. or.. 

 Hooker & Thomson (lib. Stockholm., Uppsal., 

 Lund.), Corea, Port Chusan, 59, Wilford (hb. 

 Stockholm.), sterile, pollen richly developed, 

 but to the greatest part of wrinkled grains! 

 Japan, 63, Maximo wicz (hb. Stockholm.). — 

 Africa, Madagascar, Humblot 330 (hb. Lund.). 

 The habit-figure in Graebner, Potamog. 1907, 

 47, fig. 14, A, seems to me to represent the 

 Madagascar plant. Natal, in riv. Umschlangwe 

 pr. Phoenix, 93, E,. Schlechter, n:o 3125 (hb. 

 Ziirich, Stockholm.). N. O. Rhodesia, Bang- 

 weolo-Lake, Chirni-island, 11, R. E. Fries, 

 N:o 1024; Kunene bei Humbe, 99, Baum (hb. 

 Stockholm.) v. major Benn. 



Fig. 59. P. Viisei/i Robr. A, Top of a submersed 

 stem-leaf, \^. B, Transverse section of a subm. stem- 

 leaf below the middle, ^ J". C, Marginal part of this 

 leaf, (;a. ^J'^, «', side-nerve, sir, marginal bast-bundcl, 

 /, lacuntB. />, Transverse section of peduncle, eh, epi- 

 dermis and its one-celled pseudo-bypoderma, f, lacun:c; 

 in the middle the four vascular bundles, vh, Y'. A', 

 Pistil, side-view, '/• ^^ Fruit, side-view, J. 



P. Vaseyi Robbins. 



Ap. Gray, Manual of the Botany of the north U. S., 1867, 485. — Fig. 59. 



The stem of this species commonly prolongs itself by one or two short spike- 

 bearing branches consisting of only one internode, by which the plant becomes very 

 few-spiked (1 — 3 spikes). The lower branches do not seem to come to a spike-bearing 

 development but determine themselves by turios. These turios can scarcelj'^ be di- 

 stinguished from those of P. javanicus and miduhikimo. They are usuallj^ small, 

 transformed branches in the leaf-axils. Submersed leaves 3-nerved traversed by 



