238 



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



Fig. 111. P. lacfus L, form with 

 veiticiliate leaves. Anatomical diagram of 

 the vascular bundles of the central cylin- 

 der v^. 



Lastly I will remark that I have seen a verticillatus- 

 form of P. lucens from the Nibsa in Denmark with four 

 leaves placed in a verticil round the stem. In the 

 central cylinder it exhibits four free large vascular 

 bundles running in the centre, and three peripheric ones 

 belonging to lowest leaf next above, besides which the 

 traces of the other three leaves are crowded in a separate 

 quarter. The figure 111 gives an idea of the compli- 

 cated arrangement of the bundles. For the rest the 

 anatomical conditions are normal. 



P. lucens L. X iiataiis L. 



(P. sterilis n. nom. — P. natans x lucens ex Beeby, On P. jluitans Roth in 

 The Journ. Bot., 1890, 204. — P. lucens X natans {P. jluitans Auctt.) ex RAUNKiiER, 

 Danske Blomsterpl., I, 1896, 97. — P. Noltei Fischer, vide infra!). 



Caulis ssepissime altus robustus ramosus. Folia subm.±longe petiolata inte- 

 gerrima laminis longis anguste — angustissime lanceolatis ; suprema ssepissime ± coriacea 

 petiolis lamina typice brevioribus, basi in petiolum ± angustata, conspicue et ± acute 

 cuspidata. Ligulm 5 — 9 (15) cm longae bicarinatae ± persistentes. Po?Ze?^ semper sterile. 



The English authors Ar. Bennett and A. Fryer have used the name P. 

 jluitans of this hybrid. F. Buchenau, Flora nordwestd. Tiefeb. 1894, also considers 

 part of the ^ jluitans >> -iorms to be the hybrid lucens X natans. Of the earlier authors 

 E. F. NoLTE and E. Fries likewise have evidently had this hybrid in view when 

 mentioning P. jluitans. S. Liljeblad, again, in Utkast till Svensk Flora, 1798, 

 describes the hybrid P. gramineus X natans under the name jluitans; but according 

 to J. E. Smith, Flora britannica, 3. 1391, P. jluitans is supposed to be P. alpinus 

 Balbis, and in Pursh's Flora Americse septentr. 1814, it is obviously about P. 

 Nuitallii. — G. Fischer has first signed this hybrid with a proper name : 2>P. Roihii 

 Bennetts (which name Bennett has not distributed) later rejected for the name 

 P. Noltei (Mitteil. n:o 32 der Bayer. Bot. Ges. 1904, 375) which name Bennett 

 really used in 1890 of P. gracilis Fr. To Fischer is »der fertile und der sterile 

 P. jluitans doch auf einen gemeinsamen Typus oder Stamm zuriickzufiihren» (G. 

 FiscH., Bemerkungen etc. 1914), and consequently he writes: »P. jluitans proles I 

 (=P. nodosus PoiR.)» and »proles II Ratinkiceri», with which he includes the var. 

 typicus Bge, the var. sublucens Bge, and »P. Harzii», of which all, see below! 



Like its originators P. sterilis is usually branched and of high growth but va- 

 ries otherwise in habit especially as to its upper half, where it now approaches to P. 

 natans with abundant, now to P. lucens with very faint evolution of floating leaves. 

 Usually it keeps a medium between the two, then having one or a couple of rather 

 distinct subcoriaceous leaves, which always are thinner than in P. natans. In part 



