ioo THE FACTORS [Part I 



of plants, their absence from a substratum rich in lime is quite compre- 

 hensible. It is not less intelligible that many species, although not specially 

 requiring lime, are restricted to a calcareous soil. As with the halophytes 

 in relation to sodium chloride, it is the fugitives from the struggle for 

 existence which, on a silicious soil, are unable to maintain themselves 

 against stronger competitors, but endure a calcareous soil better than they. 



That the peculiar character of the flora of calcareous soil depends in 

 the first place on its chemical properties would never have been doubted 

 if the same species of plants always behaved in the same manner ; this, how- 

 ever, is only to a limited extent the case. Only those species to which lime 

 is poisonous are always absent from a calcareous soil ; as regards other 

 species, the difference between a lime-flora and a silica- flora is not constant, 

 as it is between halophytes and non-JialopJiytes, but varies with the locality. 

 In a region with several kinds of soil, but with the conditions determining 

 the existence of vegetation otherwise the same throughout, there are 

 always certain species of plants found only on calcareous soil, and others 

 only on silicious soil, whilst a third group is more or less indifferent. Lists 

 of the three groups in any particular district will be only partially valid in 

 a second district. Many a calciphobous species of the first district is calci- 

 philous in the second, or the reverse, and many species that in one district are 

 selective in the matter of soil appear in another district on any kind of soil. 



Bonnier, for instance, found that the lists which had been drawn up 

 for the Swiss Alps, of plants more or less confined to a certain kind of 

 soil, were no longer completely valid in Dauphine. Much less do they hold 

 good for the Carpathian mountains or for Scandinavia. Thus the larch in 

 Switzerland and the Tyrol prefers the most primitive rocks, which are poor 

 in lime, and is seldom found on limestone ; whilst in Bavaria and Salzburg 

 it is quite commonly found on calcareous but not on silicious soil ; again, in 

 the Carpathian mountains it grows on all kinds of soil indifferently. 



Literature presents a fairly large number of similar cases : ' Pinus montana, Mill., 

 in its varieties uncinata and Pumilio, is a decidedly calcicolous plant ; there [in the 

 Swiss Alps] it alternates, markedly according to the substratum, with Alnus viridis. 

 The mountain pine produces its dwarf forests on the rubbly slopes of the limestone 

 rocks, whilst the alder clothes the declivities of the primitive rocks. In the Carpa- 

 thians, on the contrary, the mountain pine is indifferent as to the soil ' (Christ). 

 The following species are, according to Wahlenberg, confined to calcareous soil in 

 the Carpathians, but are indifferent in Switzerland, according to Christ : Dryas 

 octopetala, Saxifraga oppositifolia, most of the alpine Leguminosae, Gentiana 

 nivalis, G. tenella, G. verna, Erica carnea, Chamaeorchis alpina, Carex capillaris. 

 Bupleurum stellatum, and Phaca alpina, are confined to calcareous soil in the 

 Carpathians, but prefer silicious soil in Switzerland. Geum reptans, according 

 to Bonnier, grows in Savoy (Mont Blanc) exclusively on calcareous soils, in Dauphine 

 exclusively on silicious soils ; in Switzerland it appears to be indifferent. 



