112 B Canadian Arctic Expedition, 1913-18 



with respect to the other species of which the habitat, as mentioned above, 

 speaks in favour of a centre farther south. Moreover, the fact that it is associ- 

 ated with two closely allied species in southern Europe, seems to indicate a 

 southern location of the centre of distribution, in Europe rather than in Asia or 

 America. 



In outlining the geographical distribution of Hippuris (see Table 1), I 

 might just as well quote from Bentham and Hooker's great work "Genera 

 plantarum," in which it is given as follows: "Species 1 vel. 2, aquarum 

 temperatarum et frigidarum Europae, Asiae mediae et boralis, et Americae 

 borealis et Antarcticae incolae." And to these data may be added that it is 

 circumpolar. Hippuris was found by Kjdlman at Pitlekaj on the north coast 

 of Siberia, Lat. 67° 5'; in Greenland the typical plant is rare and confined to the 

 southernmost part at about 60° N. L.; the variety maritima Hartm., on the 

 other hand, is known from the west coast of Greenland between 60° and 70° N. L., 

 and on the east coast it has been reported by Dus^n from Hurry inlet (71° N. L.), 

 and by Hartz from Scoresby sound, at the same latitude. We have thus in 

 Hippuris an excellent illustration of the remarkably wide range exhibited by 

 many freshwater and even marsh species. Several other examples might be 

 recorded but I shall confine myself to mention a few, for instance: Hydrilla, 

 of which the only species, a freshwater plant, is known from tropical Asia and 

 Australia; Vallisneria, common to the temperate and warmer regions of both 

 Worlds; Hydrocharis, common to Europe and Asia; Enhalus, from the seashore 

 of Ceylon to the seashore of Australia; Ranunculus nutans C. A. Mey., from 

 Colorado (Twin lakes near Leadville), known also from Siberia (Altai and 

 Baikal); finally, Caltha natans Pall., from eastern Siberia, Baikal mountains, 

 Jenisei, furthermore on this continent: Minnesota, and, in the Northwest 

 Territory: Peace river tributaries near Fort St. John, Methy portage, at about 

 57° N. 'L. How these and many other aquatic plants were dispersed so as to 

 acquire such enormous 'distribution has been explained by Darwin (Origin of 

 Species ), the means of dispersal being notably wading birds. However, as has 

 been mentioned in the preceding pages, migratory birds may well be capable 

 of dispersing seeds or shoots of aquatic plants from one. point to another, thus 

 covering areas of no small extent even during a single season, but from what we 

 have learned about these birds, when migrating, in the stricter sense of the word, 

 dispersal, from one continent to another, does not seem probable. 



Bupleurum americanum C. et R. is credited to the American coast of Bering 

 strait where it was first found by Chamisso and Eschscholtz "ad promontorium 

 Espenberg," furthermore, to Alberta, Montana, Idaho, and Wyoming; accord- 

 ing to Macoun's Catalogue (I.e.) it has been collected at Fort Selkirk, Yukon 

 river, at the foothills of the Rocky mountains (Lat. 49°), and east of the Mac- 

 kenzie river (Richardson). Ledebour (Flora Rossi ca) considered the species to be 

 identical with the South European B. ranunciiloides L., and so did Hooker (Fl. 

 Bor. Am.). 



Meanwhile the Montana plant has been described as 5. purpureum Blankin- 

 ship, but the characterization of this as well as of B. americanum is not very 

 clear as compared with any of the Old World species, not even with B. ranuncu- 

 loides L. 



The genus contains about 60 well marked species but 90 have been des- 

 cribed, according to Bentham and Hooker. There are about 8 perennial species, 

 among which B. ranunculoides inhabits the Alps of Switzerland, about 16 the 

 Pyrenees; and several are also reported from temperate Asia and the tropical 

 mountains. 



B. ranunculoides has not, so far, been recorded from northern Asia, while 

 Ledebour enumerates several others from Altai, Baikal, and Davuria. It would 

 seem rather singular if B. ranunculoides really occurred on this continent, since 

 it is absent from Asia. And it would seem just as strange if the genus had 



