246 RIKARD STERNER 



the suitability of establishing certain limits for the distribution of plants determined 

 by the climate, even if they are meant to be schematic. It seems rather that, 

 within a zone of considerable latitude, the climate may become more and more 

 unfavourable to a species, in which case the species reaches within this zone a 

 distribution-limit which is further determined as to its position by the climate in 

 cooperation with several other factors, hor alpine tree-limits De Candolle has in 

 vented the term »zone contestee» ; Schroeter and Fries speak about a »Kampf- 

 zone» (Fries 1913, p. 152). Hence the establishment of such a zone should theo- 

 retically be much more appropriate regarding the horizontal distribution of species. 



As Brockmann-Jerosch (I. c.) has pointed out, maritime districts have great 

 possibilities of satisfying plants with an otherwise quite different distribution. In 

 Great Britain, for instance, we find Atlantic, Mediterranean, Arctic-alpine, and 

 Steppe species in the \icinity of each otiier. On the other hand the continental 

 climate is unfavourable and weeds out many species. Several West European 

 .species have easterly distribution-limits which have undoubtedly their chief cause 

 in the climate. Ilex aquifolium and Ulex europaeus suffer badly from frost when 

 grown outside their eastern limits in Middle Europe (Grisebach 1. c, p. 97). 

 Probably the eastern limit of the beech too is climatic (Brockmann-Jeroscii 1. c). 



As regards the western limits of continental species, on the other hand, a 

 climatic character would seem very difficult to establish. On the whole, the species 

 in their most extreme localities show no noticeable consequences of anv dis- 

 advantages in the climate, and many continentally distributed species have proved 

 able to thrive when cultivated in maritime districts. Hence continental species 

 should have a great climatic amplitude. The reason why continentally distributed 

 s[)ecies can be distinguished should be found in otiier ([uarters, for instance, in 

 their demands regarding the nature of the soil, in the migration history of the 

 species or in the rivalry which they have to endure with species tied to mari- 

 time districts. 



Notwithstanding all this, it may be supposed that behind other more obvious 

 limit-forming factors there may be a certain disadvantage in the chmate. It is 

 not very palpable, yet it may, for instance, render the species inferior in the 

 struggle for space. 



What has been said here, however, is valid onh' about the direct connection 

 between the climate and plants. Indirectly, of course, the climate has very great 

 importance, above all through its influence on the nature of the soil. 



Even if generally the direct influence of the climate on the distribution of 

 continental species cannot at present be proved, it would seem appropriate to 

 make an account of the ecological features which, because of the climate, ought 



