90 PLANT GEOGRAPHY 



and species. This is exemplified by the numerous 

 endemic genera of the Andes, many of which are mono- 

 typic, or have but few species: in such isolated plants 

 as the monotypic Passifloraceous Guthriea capensis Bolus, 

 and the many endemic Composite and Ericacecs on the 

 Schneeberg in Cape Colony ; and by the floras of Kilima- 

 njaro and the Abyssinian Highlands. It is not a suffi- 

 cient explanation of this large endemic element in 

 mountain floras to say that it is due to the variety of 

 station that mountains present. As in the case of 

 islands, it would seem that isolation and its concomitant, 

 a comparative absence of competition, have facilitated 

 the origin of new specific forms. 



The sub- Arctic mountains of Iceland, Scandinavia, 

 and Kamtchatka do not yield the same wealth of 

 endemic forms ; but, in addition to these richly endemic 

 mountain floras, we have, especially in the Northern 

 Hemisphere, evidence alluded to in one of our earlier 

 chapters of a flora originating in polar latitudes then 

 warmer, driven south or east by the advance of Glacial 

 cold, and, to some extent, returning as the climate 

 improved. From this we have the curious result that 

 some species of Primula, Pediculans, and Oxytropis are 

 now found only on the southern slopes of the Alps. (See 

 Book i, chapter v.). 



* CHAPTER X 



WATER-PLANTS 



ALTHOUGH there are brackish- water estuaries in which 

 marine Algae mingle with shore Spermatophytes, the 

 main practical distinction among water-plants is that 

 between fresh and salt waters, which is approximately 

 one between Spermatophyta and Algae. Another dis- 

 tinction of primary significance is that between Benthos, 

 or rooted plants, and Plankton, those that are free- 

 swimming. 



There are all degrees of transition between the her- 

 baceous flowering plants that inhabit marshy ground 

 and the water-side, and those which live in the water 

 itself; so that aquatic Phanerogams may, in a wide 

 sense, be termed an integral part of the land floras. 



