194 



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



the other factor must have wanted them, since the hybrid has verv much reduced 

 upper leaves. The very narrow and long submersed leaves point in the direction 

 of P. natans and some narrow- leawed species. Superficially observed these leaves 

 seem to be 7-nerved, but as the figure below shows, the vascular bundles are in fact 

 only three. The same figure also shows t hat these leaves are very rich in scleren- 

 chymatous strands. The apexes of the submersed leaves varv from rather acute to 

 ioundlv obtuse, see the figure! The ligules are strongly nerved, dark-green, and in 



the front-field five-nerved. At their base 

 there are prominent glandulous swellings 

 (nodal vittae or oil-eells). The stem is 

 high-grown, terete, at the middle thread- 

 like. It prolongs itself by one single 

 spike-bearing branch. The spikes are 

 small, 3— 5-whorled. All these proper- 

 ties taken togethcr undoubtedly allude 

 (o the combination written above. 



Tf nevertheless there would be any 

 hesitation in admitting a crossing between 

 one of the largest (P. natans) and any 

 of the most delicate species it must 

 disappear on the discovering, in the 

 hybrid, of cauline turios, evidentlv like 

 thosc characteristic of some small-leaved 

 species. A doser examination proves that 

 no other species but P. trichoides togethcr 

 with P. natans has becn able to produce 

 such turios. The figure gives a better 

 idea of it than any description can do. 

 In a surprising way the stem ana- 

 tom)' also confirms the morphologic and 

 biological testimonies. The central cylin- 

 der of stem, t hus, has now (in narrower 

 internodes) an arr angemen t of bundles 

 quite as in P. trichoides, now, again, it is 

 intermediate between the two: witli 2 free median and 2 free latera] bundles. The 

 subepidermal strands are also full-numbered and Btrong; in the bark, moreover, 

 there are one or two eircles of bundles, which can be said to be a reduetion of the 

 circumstances of /'. natans, in which we usually lind three or four eircles. The en- 

 dodermis- cells are, in all the cases examined, //-cells as in P. natans. The anatomy 

 of the peflunclc corresponds most closely with that of /\ natans with a reduetion 

 of the aumber of bundles here, fcoo. The cross-section can be said (o exhibit a /'. 

 natans in miniature. 



The anatomv of the submersed leaves will be rendered olear l>v the figure 



Fi(,'. <J7. /'. variifolius Thobe .1, <i, h, c, </, Different forms 

 of Boating leaves, \. is, «, //, Topa of snbmerseJ leaves, 1 ,°. 

 C, Part of ii submersed teal ;it the middle, lacunar system aud 

 snperflcial Bclerenchyma (snbepid. str.) visible, ",''• ö, Transverse 

 Bectioo oi n submersed leal at the middle, showing the arrange- 

 iii • ii t oi the lacunte aud the Bubepidormal strands, us, upper, and 

 Is, lower surfaee, m, miduerre, til lateral aerves, str, bast bun- 

 ■ II. h, r ,". /:, Tui k., a. stem, b, leal. v', gland, \. 



