252 RIKARD STERNER 



steppe species) are generally found only in localities that are in some respect 

 or other developed to great extremes, for instance, through a high electrolyte 

 percentage or a low degree of dampness in the soil. One has a right to believe 

 that the species that prefer such habitats must be specially equipped. On the 

 other hand, those species may occur under very different habitat conditions, and 

 when cultivated, they prove to be but little specialized concerning the nature 

 of the soil in the respect mentioned. At the same time it is often a characteri- 

 stic of the mode of occurrence of these species that they form part of a sparse 

 vegetation, where, because of certain extreme habitat features, the production of 

 individuals is not great enough to occupy the whole area, and where the com- 

 bination of species in the vegetation would seem to be determined less by a selection 

 among many species during a struggle for space, than by the existence of such 

 species as can stand the extreme type of habitat. Hence the species have no 

 greater use for a capacity of competition and may to a certain degree be sup- 

 posed to be without it. They may perhaps be looked upon as forming a pariah 

 ^ class in the plant world, forced back to the »worst», inhospitable localities where 

 they are able to exist. The fact that such localities may occur edaphically even 

 outside the steppe districts, in conjunction with the dispersal capacity of the 

 species, may perhaps to a certain extent explain the distribution. 



The connection between a continental nature of the soil and the ecology, and 

 probably also the distribution, of continental species, would consequently seem 

 to be capable of being thus summarized: continental species generally occur in, 

 and seem to be confined to, soil with a high amount of electrolytes (especi- 

 ally of lime) and often al so with a low degree of dampness. The species ma}' be 

 supposed to be dependent on the physical attributes of the continental soil-type; 

 and they are able to endure the qualities, unfavourable to other species, that 

 often characterize this type of soil — for instance, a high amount of lime and an 

 inconsiderable degree of dampness. 



A few words about continental geographical conditions and the general 

 features in the distribution of continental species in Europe. 



The steppes of South-East Europe form the most continental type of scenery in 

 Europe. These steppes are above all caused by the rainfall conditions. The 

 rainfall on the steppes is, speaking absolutely, not scanty, but its distribution 

 makes it almost ineffective. 



Besides this the continental character of the climate appears in a high summer 

 temperature and a sharp division of the year into a season (or two seasons) of rest 

 and a vegetative season (or two vegetative seasons), and also by a low comparative 

 dampness and a scanty cloudiness. The steppe soil is chiefly to be classed with 



