THE CONTINENTAL FLORA OF SOUTH SWEDEN 227 



In the book mentioned (for instance, on p. 562), however, Grisebach has pointed out 

 that some species might be so young that they have not yet attained their full 

 area. 



In his later works Grisebach has to some extent changed his opinion. In «Die 

 Vegetation der Erde» (1872) he says (p. 76): »Die Vegetationslinien entsprechen 

 denmach nicht immer dem Verlauf bestimmter klimatischer Grenzwerthe, sondern 

 dem Zusammenwirken mehrcrer», and he points out that certain limits of distri- 

 bution are »nicht bloss durch die Lage der Vegetationslinien, sondern zugleich 

 durch Untersuchungen iiber die Lebensbedingungen der einzelnen Arten zu er- 

 ledigen» (p. 98). 



Here attention may be drawn to a work of considerably later date, W. Koeppen, 

 »Versuch einer Klassifikation der Klimate, vorzugsweise nach ihren Beziehungen 

 zur Pflanzen\velt» (igoo). Types of climate are in this work distinguished in accord- 

 ance with the distribution of species and the character of the flora. 



Even so early as the middle of the nineteenth century a new tendency appeared 

 in floristic phytogeography. It is characterized by the view that many phenomena 

 in the present distribution of species cannot possibh' be explained solely by the 

 aid of forces now existing; great importance must be attached to geological causes. 



E. Forbes and the above-mentioned A. De Candolle must be looked upon as 

 the originators of this trend of opinion. By studies in the flora of Great Britain 

 Forbes had (1846) found a great number of disjunct areas, a fact which, he thought, 

 could only be explained by the areas having been split up by revolutions in the 

 distribution of water and land or by changes in the climate. Species might be 

 relics of an earlier flora, and their present distribution is connected with the for- 

 mer one and that of their nearest forefathers ; hence there are geological causes 

 for the present distribution.^ 



In a somewhat modified form Forbes's opinion became prevalent during the 

 latter part of the nineteenth century, and it maj- be said to be the opinion of 

 the present day too. During that time Ouarternary geology and palaeontology 

 have passed through a grand evolution. The great results attained in these 

 domains have naturally been able to clear up many obscure phytogeographical 

 problems; and taxonomic phytogeography has of course been to a great extent 

 concentrated on studies of the connection between the present distribution of 

 species and their phylogeny or earlier geographical conditions. 



Thus, the possible geological causes of the limits of distribution have above 

 all attracted interest and have been accorded the greatest importance. In this 

 connection, in fact, it may justly be said that phytogeography has man}' a time 

 assumed a much too theoretical and speculative tendency. At the same time, 

 however, a great number of new and valuable experiences have been made. Be- 



' As regards the divergent opinions of Forbes and Grisebach see further, for instance, Kerner 1S79 



