116 



J. O. HAGSTRÖM, CRITICAL RESEARCHES ON THE POTAMOGETONS. 



tomy is chiefly the same as in the next forcgoing and following species. The devia- 

 tions lie in the fact that the vasal bundles of the central cylinder distinctly divide 

 into two lateral and two median bundles, that a single cell-layer or hypodcrmatic 

 supporting stratum sometimes exists in the borders of the stem, where, in such a 

 case, the strands also appear in a greater number, finally that rarely one or a few 



faint interlacunar strands occur un 



a 



.OöOQ 



a 



str 



both sides of the central cylinder 

 in the börder-segments of the cross- 

 section. In the pedunele the bundles 

 run separate from each other, the 

 c two median ones approximated, the 

 lateral ones more remote from the 

 cent re. No partit ion of the lateral 

 bundles has been observed. A sup- 

 porting layer is present, whereas 

 the subepidermal strands are absent. 

 The pedunele has the same shape as 

 the stem but is a little fchicker. 

 The rootlets lack sclerenchymatic 

 tissue and air-channels. 



The rhizome is very slightlv 

 compressed in this species also. The 

 bundle system of the central cylinder 

 is reduced to a compound bundle, 

 surrounded by an endoderm of rather 

 thin-walled (J-eells. In the eortex 

 the lacunar system is reduced to 

 nearly a single cirele of narrow la- 

 cunse, outside which the cell-tissue 

 is more compact. Subepidennally 

 therc are scattered faiut sclerenchy- 

 matous strands (see fig. 51, C!). 1 



Respecting the anatomy of the 

 leaf I refer to the figure. In the 

 upper part of the leaf fche Lacunse along the midrib gradually disappear. The tnidrib 

 and tlie lateral aerves linaliv grow very faint and join in fche very apex. In the broadei 

 leavea fchere is not seldom a faint nerve wifhin or uithout fche proper lateral aerve, 

 in which lätt er case the leaf bears a ccrtain resemblance to a mucronatus-lesi. Those 

 secondary lateral aerves, however, usually anastomose vrith fche chief Lateral aerves 



Fig. 51. P. obtusifolius M. & K. A, Transverse seo- 



tiim oJ a atem-leaf at the middle, h , n . B, Top of a stem- 



le.if, j. C, Transverse seetion ol the rhizome, ',". /', 



Pistil, (/, side-view, /', from the back, 1 ,°. /■.', Transverse 



stionofthe Btem, *,", * aooidentallj ooanrring bast-bnndles. 



Ill /<', snrface section of tlio atem-epidermis, ,". '•'. Bnrface 



■,, ,-t. of the epidermis of the pednnele, '\ u . II Transverse 



- ion throngh the leaJ and ligule at the very base 



immediatelv ahove the insertion point and before the 



development >ii the bast-hnndles in the upper Borface of 



i lio leaf and in tlir inti ivai mal part of the lignle has 



taken plaoo. Tlic .siibi-piilerinal strands ol the Btem eon- 



tinne in the lower snrface ol the leal and in the wing- 



Beld of tim lignle. Of the tig. 27!, '■'<•; m, midvein, «', 



i inTii', str, bast-bnndles, /. lacnna), ee, central stele, 



ic, interearinal pari (front field), r, ridge-part. K, Yonng 



lignle, J. 



' The rhizome deacribed and figured by C. W. Foktell in hia Beiträge etc. (Taf II, t'. 55) ia the basa) 

 portion of a lurio and not a true rhizome, which, besides, is ;i very rare occurrence in Uiis speciea ;^ well ;is 

 in all iis alliea 



