144 



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



Museums. F. ovatifolius from Brandenburg, gathered by Buchenau (hb. Lund.). 

 Specimens, however, are also present from England, Russia (St. Petersb., Osiha, Po- 

 land), France, Austria and Sivitzerland (higher mountain-lakes). 



From N. America there are specimens from Canada, Brit. Columbia, and from 

 the States, Nov. Ebor., Tuckekman jr. (hb. Upps.); Lewis Creek ad Ferrisbergh, 

 Vermont, 81, Faxon (hb. Stockholm.); California, S. Francisco, 74, Eisen (hb. Upps.). 



P. alpillllS Bale, x Cl'ispus L. (P. veilllStllS Baagoe, Preparation des Hydroph., 

 in Actes du Congres int. de Bot., 1900, 517, nomen solum. — P. Baagoei Ar. 

 Bennett ap. Graebner, Potamog., 1907, 132, nomen.). — Fig. 64. 



As in P. icndulatus Wolfg. the stem of this hybrid is also a 

 little flattened and on either side furrowed, by which appears its 

 relationship with P. crispus. The anatomy also answers to that of 

 P. crispus in the parts in which this species deviates from the 

 P. alpinus, namely in the central cylinder, where the lateral bun- 

 dles are more reduced so that the crosscut-form becomes oval, whereas 

 in P. alpinus it is square with rounded corners. The epidermis has 

 also the pseudo-hypoderma found in P. crispus. The characteristic 

 of both species, viz. the complete absence of cortical bast, is to be 

 found here too. The peduncles and spikes remind of P. crispus in 

 a high degree. This species appears in the ramification also and in 

 the complete absence of floating leaves and petioles in the upper 

 leaves, which, however, occasionally have the base tapering like a 

 Fig. 61. p. venus- stalk. Au influcncc from P. crispus can obviously be traced in the 

 tus baag a. Top of niidrib of the leaves too, but, for the rest, the nervation is an 



leaf, a little enlarged. 



B, Marginal epidermis- inheritance from p. alpinus, although with some reduction as to 

 or dilatation of the cell the numbcr of the lateral nerves by which the leaves in general 

 to'ifnueuiation.'^""""" bccomc 7-nerved. P. alpinus appears also in the intermediate ligules 

 and, above all, in the slightly crisp leaves with smooth margins. 

 Only in the very youngest leaves and by higher enlargement a faint disposition to 

 denticulation can be observed by a slight swelling of the marginal cells at intervals. 

 — The pollengrains have the same size and shape as in P. alpinus but merely a few 

 grains are fertile. Styles and stigmas, on the contrary, remind of P. crispus, the latter, 

 however, often abortive. Turios are not observed either in the stem or the branches. 



This hybrid can easily be mistaken for P. crisjnis X pnelongus, which, however, 

 has more whitish-green ligules, more rounded to cordately rounded leaf bases very 

 obtuse apexes, whereas P. venusius has brownish-green ligules, narrower lanceolate 

 or lance-oval leaf-base, in the upper leaves somewhat stalk-like, and not quite so 

 rounded apexes (see the fig. !). The very most significant character is the perfect 

 absence of sclerenchyma in the bark of the stem. 



Distribution. Denmark. Ssell., Vigersdalsa, 96, Ferdinand, 99, Baagoe (hb. 

 Stockholm., Upps., Lund.), Jutl., Gudena in Lillea at Logstrup, 99, Baagoe (hb. 

 Upps.). More stations than these are not known as yet. 



