THE CONTINENTAL FLORA OF SOUTH SWEDEN 235 



Here it will only be pointed out that the species, like other continental species, 

 are rather heliophilous: that is to say, the most important of the life manifesta- 

 tions of the species take place at a time when the intensity of light is at its 

 height, before the trees are covered with leaves and the shade has become too 

 strong. It is remarkable that, in accordance with this, certain of the species may 

 be comparatively widely spread in the South-East European steppe districts, where 

 they are found in the thin » steppe woods» or steppe-scrubs (see, e. g., Alechin 

 1909 and 1910), 



The early flowering »grove>' plants without continental distribution are chiefly 

 species that reach far up into alpine regions, wOiere they form part of an unshaded 

 or hardly shaded ground vegetation. 



Survey of the distribution of continental species in Europe. 



With the great range here given to the continental element, the species be- 

 longing to it will show important differences in their distribution. A great number 

 of continental types of distribution may be distinguished. 



A grouping of continental species according to their general European 

 distribution meets with great difficulties, transition types always being numerous. 

 A primary ground of classification, which may a priori seem suitable, is the dis- 

 tribution of the species in East Europe: does it here belong to the steppe 

 districts, or does it exist chiefly in the Central and North Russian forest district? 

 This topographical classification would coincide fairly well with one founded on 

 the mode of occurrence and would naturally involve considerable differences with 

 regard to the distribution of the species in other parts of Europe also. I have 

 decided to use this as a primary ground of classification. Hence in the first 

 place we get a group of southerly species, which we style meridional, and a group 

 of northerly ones, styled Boreal. 



The latter, however, might vary much with regard to the extent of the distri- 

 bution towards the north. Hence a division of the group into two would be ne- 

 cessary. One of these groups would comprise species whose northern limit of 

 distribution coincides with that of the oak, the other would comprise species widely 

 spread even in Subarctic Russia (in Engler's sense of the term). The former might 

 be called Euboreal, the latter Subarctically Boreal. 



The meridional species belong chiefly to the steppe vegetation. Among other 

 types of vegetation represented in this group, the flood meadows should be 

 specially pointed out. These are very conspicuous along the South Russian rivers 

 and have a peculiar flora (e. g. Krassnov 1887, 1889; Kuznecov, 1901). The 

 boreal species belong to a large number of vegetation types, in the first place 

 forest associations of various kinds and marsh associations. 



