THE CONTINENTAL FLORA OF SOUTH SWEDEN 373 



Water-plants. 



In my dchnition of water-plant associations I follow Warming (1909, pp. 149 ff.). 



As regards the composition of the water-plant associations in Russia I desire 

 to give the following references to the literature of the subject. Flerov 19 10 

 (e. g. the lists 279, 309, 570, 615, 726, 766, 769), Borovikov 1906 (the Donetz), 

 Korshinsky 1888, Krishevsky 19 12 (Kherson), Naumov 1903 (Kharkov), Saljcssky 

 1900 (Orel), Sidorov 1897 (Ekaterinoslavl), Sukaczev 1903 (Kursk). 



The species falling under this head possess, as a rule, very extensive distri- 

 bution-areas. Many are rare, with their occurrences scattered over vast areas. 

 With regard to the distribution of the species in Middle Europe, however, it 

 seems as if no inconsiderable number of species had a more or less maritime 

 distribution, while the continental flora includes only some few representatives. 



Thus while of about 75 water plants in South Sweden only 58 % are found 

 in the Government of Kazan and 70 % in Silesia and England, out of the ^-ij 

 species or so in the Government of Kazan, 36 are included in the flora of Si- 

 lesia, 34 in that of South Sweden, and 32 in that of England. To some extent 

 perhaps this has its cause in the fact that species may have been overlooked in 

 the somewhat imperfectly known flora of Russia. 



Perhaps, however, in this circumstance we may see an illustration of the pro- 

 nouncement of Brockmann-Jerosch cited above on p. 246, namely that the 

 climate can to only a very slight extent be the direct cause of the absence of 

 continental species in maritime districts. That this is the case may stand out 

 very distinctly with regard to water-plants, for obviously they have very good 

 dispersal-power, as a rule, and their requirements with regard to nature of the 

 ground (water) can be satisfied to a far higher degree than those of land-plants 

 irrespective of a continental or a maritime development of the climate. 



As regards the continental species of this group in the south of Sweden I 

 have not much to say, especially as a monograph on the distribution conditions 

 of water-plants in Sweden is in process of elaboration by another writer. 



Of the few species which can come into question here, of course, Trapa nataris 

 immediately attracts attention. But as the distribution of the species as a fossil 

 falls outside the scope of the present memoir, and as moreover there has recently 

 been published an exhaustive account of the species (Malmstrom 1920, where 

 the distribution map is to be noticed), 1 have nothing to say in this place. 



Elatine triandra Schkuhr is another waterplant which may probably be treated, 

 with more or less certainty, as a continental species. The species, however, is 

 probably not yet sufficiently well known as regards its general distribution; it may 

 have been overlooked in many regions, especially in Russia (cf. Appendix I). It 



