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



171 



str 



str 



str 



Fig. 88. P. repens Hagstr. Longitudinal 

 section through a node, schematized; explana- 

 tion see above! a, stem, b, leaf, ic, ligulc, 

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

 vbic, vase. bnndles of tho lignle, vbus, those 

 of the upper, and vhls, of the lower snrface 

 of the leaf, mb, midvein of the leaf, vbie, 

 bnndles of the wing-field of the lignle, str, 

 Fig. 87. P. repens Hagstr. A, Top of a leaf, J, showing snbepidermal bast strands of the slem. 



the form and nervation. B, Young lignle, J. C, Transverse 



section of part of the epidermis and its strengthening layer, the COrteX illtO tlie Central Cylinder, aild the 

 r 'j , ep, epidermis, lip, psendo-hypoderma, str, bast bnndle. . . 



v, Transverse section of the central steie, y>, showing the same is also true concerning the leai. JMot only 



vascular bnndles and the interjacent mechanic tissne. E, f i rnidvpin nnrl thp Ipfprfll VPl"n<5 PntPr HlP 



Transverse sect. of a leaf at the middie and, f, at the base, Lne micrvein ana tne jarerai \ eins enter me 



immediately above the insertion point, «; m, midvein n\ cen tral Cylinder bllt alsO the bundleS of tlie 

 principal and n", secondary lateral nerves, str, marginal bast ^ 



bnndle, vbus, bnndles of tho upper, and vbls, of the lower lower Slirface [vbls in tlie fig. 88). Tlie 



surface of the leaf (ef. fig. 88!). O, Transverse section of a, ,, cji r fjiir i 



Hguio immediately at the insertion point, 8 T °, ic, front-fieid, bundles ot tlie upper surtace ot the leai and 



wf, wing-field; the bnndles of the u-f turn their vessels to f L f f l i n f pr p flr ; n ol nflr f n f fl lp lirrnlp 



the stem-side, tho bundles of the ic towards the leaf-side ^ nos 6 or ^ n G llltercarmai part 01 tlie llgUie, 



(ef. fig. 88!). 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 alvvays 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 middie 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 väst oceans, nevertheless exhibit Potamogeton-sipecies 

 of evidently common origin. 



