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



171 



str 



str 



sir 



vbls 



Fig. 87. P. repens Haoste. A, Top of a leaf, -J, showing 

 the form and nervation. B, Young ligule, |. C, Transverse 

 section of part of the epidermis and its strengthening layei', 

 ''jO, ep, epidermis, lip^ pseudo-hypoderma, str, bast bundle. 

 I), Transverse section of the central stele, \', showing the 

 vascular bundles and the interjacent mechanic tissue. £', 

 Transverse sect, of a leaf at the middle and, F, at the base, 

 immediately above the insertion point, \P j »», niidvein, «', 

 principal and n" , secondary lateral nerves, sU% marginal bast 

 bundle, vbus, bundles of the upper, and vhls, of the lower 

 surface of the leaf (cf. fig. 88 !). G, Transverse section of a 

 ligule immediately at the insertion point, ^^, ic, front-field, 

 Iff, wing-field; the bundles of the wf turn their vessels to 

 the stem-side, the bundles of the ic towards the leaf-side 

 (cf. fig. 881). 



Fig. 88. P. repens Haoste. Longitudinal 

 section through a node, schematized; explana- 

 tion see above! «, stem, h, leaf, it\ ligule, 

 front-field, ivf, wing-field, cc, central cylinder, 

 vbic, vase, bundles of the ligule, vbtis, those 

 of the upper, and vhls, of the lower surface 

 of the leaf, mh, midvein of the leaf, vhw, 

 bundles of the wing-field of the ligule, str, 

 subepidermal bast strands of the stem. 



the cortex into the central cylinder, and the 

 same is also true concerning the leaf. Not only 

 the midvein and the lateral veins enter the 

 central cylinder but also the bundles of the 

 lower surface [vbls in the fig. 88). The 

 bundles of the upper surface of the leaf and 

 those of the intercarinal part of the ligule, 

 again, descend into the lacunar system of 

 the cortex but disappear immediately below the insertion point, and the internodal 

 part of the stem accordingly is always devoid of interlacunar bast and vascular 

 bundles. The bundles of the upper and lower surface of the leaf belong only to 

 the basal fourth part of the leaf and the cross-section at the middle exhibits an 

 appearance as is shown in the fig. 87, E. The subepidermal strands of the stem 

 disappear below the node and appear again above it as is shown in the fig. (str). 

 Only some one or other continues through the node. — Another type is described 

 and figured on p. 70, fig. 27. 



Distribution. Africa. Rhodesia in the Lake Bangweolo on sandy ground, 

 creeping by long rhizomes mostly above the bottom. 19. 9. 1911. Rob. E. Fries. 

 N:o 655. 



It is noticeable that S. America (Brazil), Africa (Bangweolo-district), Australia, 

 and New Zealand, separated by vast oceans, nevertheless exhibit Potamogeton-s^ecies 

 of evidently common origin. 



