Oalcicole and Calcifuge Species 145 



plausibility-j since the great majority of plants are highly 

 intolerant of salt soils. But in the case of calcicole and 

 calcifuge species it is highly doubtful whether competition 

 has much to do with the matter. In the first place the 

 number of calcifuge* species is not so great as to make 

 the absence of their competition a consideration of much 

 importance. And further, this theory does not explain 

 but rather conflicts with the abundance and luxuriance 

 of vegetation, other than that made up of distinctively 

 calcicole species, on suitable calcareous soils. 



It seems probable, in fact, that there is some positive 

 feature of calcareous soils favourable to vegetation at 

 large and to calcicole species in particular. Whether it 

 is the chemical characters, as such, of these soils, or 

 correlated physical characters, we do not know. This is 

 one of the problems of plant-ecology, which we may hope 

 will shortly find a satisfactory solution. 



Meanwhile we have to recognise that the calcareous 

 soils bear a characteristic vegetation, marked 

 The plant- •\^^ ^ number of species which are rarely 

 calcareous found away from them, at least in the same 



soils. region (or if found away from them, occurring 



only on special types of non-calcareous soil), 

 but generally containing also numerous " indiif erent " 

 species which are abundant alike on calcareous and on 

 non-calcareous soils. The correlation of calcareous soils 

 with characteristic plant-communities makes it necessary 

 to recognise in these soils a distinct type of habitat 

 bearing distinct plant-formations. 



The distinctive calcareous soils of this country are in 

 the first place the limestones in the wide sense, including 

 the chalk, which is a relatively pure and very soft lime- 

 stone, and secondly the calcareous sandstones and the 

 marls, which are mixtures of lime and sand and of lime 

 and clay respectively. 



In England and Wales the most extensively developed 



T. 10 



