THi: CONTINENTAL FLORA OF SOUTH SWEDEN 251 



As a nutritive substance lime is necessary to all higher f)lants. In order to 

 satisfy the »nutritive demands* of plants, however, only a small percentage of lime 

 is necessary. It may be questioned whether there are species that are really 

 confined to a higher percentage of lime in the soil (compare, for instance, Kraus 

 igii, p. 6i). The so-called calciphilous plants |»calcicoles») have in most cases 

 proved to be confined to lime only in certain districts. When cultivated, they 

 can thrive in soil comparatively poor in lime. On the other hand, many plants 

 never occur in calcareous soil and have proved quite unable to grow in such 

 soil. They arc consequently calcifuge plants. Besides these, of course, there are 

 a great number of species which do not, even in nature, show any special predi- 

 lection for either tyi)e of soil. 



Like other electrolytes, lime may cause harm to plants when it occurs in great 

 quantities. A great amount of electrolytes increases the osmothic pressure in 

 the soil fluid, and hampers or renders more difficult the absorption of water by 

 the plants. Besides, lime has in other ways an injurious influence on plants, 

 which is due, according to the results of the latest investigation, to the fact that the 

 high OH-ion concentration that accompanies a high percentage of lime, ope- 

 rates as a poison. (See for instance, Mevius 1921). In regard to a high per- 

 centage of lime in the soil, however, plants vary a good deal. 



The calcifuge species are evidently the most delicate; the calcicoles» and the 

 plants indifferent to lime, on the other hand, can endure a higher percentage of 

 lime. The fact that the formers generalK- occur onlv on calcareous soil, mav be 

 explained on the ground that on such localities they are free from rivalry with 

 other species, a rivalry which they cannot endure. 



The fact that in certain districts the species are confined to calcareous soil, 

 in others not, to a certain extent favours this hypothesis, as does also the fact 

 that, when mans intervention keeps the rivals away, some species thrive excel- 

 lently in comparatively limeless soil (provided, of course, that the physical qua- 

 lity of the soil is not the cause of this). Hence indifferent species should have 

 a great power of competition as well as a great amplitude in relation to the 

 lime. The lime plants would seem to have only the last-named quality to thank 

 for their existence. 



The continental species, above all the steppe species, in man}- cases occur as 

 calcicoles outside decidedly continental districts. The steppe species should 

 also be able to stand a high percentage of electrolytes, the steppe soil being 

 generally characterized by a high amount of electrolytes. Hence the facts that 

 these species may occur outside the steppe districts may to a certain extent be 

 caused by the existence of localities whose high percentage of lime tJiey are 

 able to stand, but not species that are superior to them in the struggle. 



In this connection it should be noted that many continental species (especially 



