ur, 



J. O. HAGSTROM, CRITICAL RESEARCHES ON THE rOTAMOOETONS. 



gramineus var. graminifolius Fr. by S. Almquist in Bot. Not., 1889, 66, are not this 



hybrid, see under P. gramineus L. — Norway, Senjen, Bryggehaug, 10, Notö. 

 P. ne ridits must until further be looked upon as a inöst rare plant. 



P. alphius Balb. x natans L. (P. Drncei Fryer, Potamog. of the British islea, 



1808, 31, t. 21). 



66, P bi "■■ i l'i. ■ i i i, Blade 

 of 1 1 • » \ onngi ■( Ii al ol ;i spike bi ai ing 

 thool . sloping .i' the base, rathei thio, [. 

 /; 'i i.' lowi st lenf bot o bai ren 



ibool rrora thi Bol öarden "i Copeuha 



:■ 



Fig. 66. 



There ean scarcely be any doubt of the hybrid 

 nature of the Berkshire plant nanied P. Drucei (Fry kr 

 1899, as a full species). The large floating leaves di- 

 stinctly indicate that P. natans is to be considered as 

 one of the or i ginators. A eloser investigation of all 

 the organs of the plant does not contradiet the sup- 

 position either. But which the other parent species 

 may be is not quite a raatter of course. The first 

 proposition of Druce on P. alpinus, however, seems 

 to be favoured with all probabilities. Thelong petioles 

 of the floating leaves certainly seem to be adverse to 

 it, but they are likely to originate from local condi- 

 tions (River Loddon). The leaf-base is sloping as in P. 

 al pin ns and in the river-form of P. natans which also 

 has long petioles. The floating leaves besides appear 

 verv early, already below the primary spike, which 

 confirms the supposition that either of the two parent- 

 specics is furnished with coriaceous Leaves. The sub- 

 mersed leaves are also long-stalked as the other natans* 

 hybrids. The Ligule ean be said to be intermediate, 

 75 — 85 mm long (I\ nul.), brown (P. alp.) with faint 

 ridges. The stylos and stigmas rcmind of /'. polygoni- 

 folius almost more t lian of natans, but the smallness of 

 l lic stigma, especially, may depend on deformity, a 

 usual occnrrence in the hybrids. Wc are so much the 

 more [nelined to think so, having s(>cu specimens culti- 

 v&teå iu the Botanioal Garden of Copenhagen with al- 

 pinu8-Bi igmas. 



A cross-seotion of a Bpike-bearing stem shows a 

 Btructure \ n y obviously confirming the presumption 

 about /'. filpiuns aml natans as the true origin of this 

 hybrid. KndodcMinis and central stclc ncaily typical 

 /'. (i/pimis, epidermis with a pseudo-hypoderma and 

 Bcattered bark-bundles influenced b\- /'. >i<it<ins. Yet 



