. Critical researches on the potamogetons. 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. Th
. Critical researches on the potamogetons. 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. 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, Maximowicz (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 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,
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