244 RIKARD STERNER 



species to tlie climate, the nature of the soil etc. should be studied. In this way 

 we may perhaps acquire some knowledge about the ecological amplitude of the 

 species, such as it appears in nature under the influence of such factors as, for 

 instance, the rivalry between species. 



To explain the western limits of continental species it is necessary to know in 

 what degree the continental geographical conditions in the climate and the 

 nature of the soil are reflected in the ecology of the species. Our knowledge 

 about this is, at present, very scanty. Nevertheless I have considered it proper 

 to compile from the literature — chiefly from well-known handbooks, such as Schimper, 

 Jost, Warming ( 1 914) ■ — a summary of what we have to lean upon in order to judge 

 the conditions mentioned. It seems scarcely necessary to point out that this 

 summary must be very incomplete and will not render possible any positive con- 

 clusions. 



The climate and the ecology of continental species. 



The search for a direct connection between the climate and the distribution 

 limits of plants has been of absorbing interest to scientists ever since phytogeo- 

 graphy first came up. For a long time people generally tried to see a rather 

 simple causal connection here. If the distribution limit of a species — generally 

 drawn up very roughly ■ — ran in agreement with that of a certain value of a 

 climatological factor, the distribution of the species was supposed to be determined 

 by that very factor. As a rule, scientists made use of thermic factors calculated 

 in many ways: in early days chiefly the mean temperature for the year or for a 

 season (Humboldt and Schouw); later on the average daily maxima and minima 

 (De CandoUe, Grisebach), or the accumulated temperature (»Die Warmesumme») 

 of the species, i. e. the temperatures ascertained in various ways from a certain 

 date during the season of rest (for instance, the first of January) to the coming 

 of a certain function of the species (in the simplest cases maximum temperatures 

 of all days above 0° were added together) (Boussingault, Hoffmann; see especi- 

 ally Ziegler 1879) or the length of the vegetative season (Grisebach). 



In recent times this mode of thinking of the connection between the climate 

 and the distribution limits has been looked upon very critically. The objections 

 that can be made seem to be briefly as follows: 



1. The distribution-limits of species must in the first place be sufficiently well 

 known, which has hitherto not been the case many a time. 



2. The meteorological material suffers from great defects. The report from a 

 meteorological station may differ in a high degree from the conditions in a 

 plant locality in its immediate neighbourhood; and it should especially be no- 



