242 THE GEOGRAPHY 



into our conceptions, and much indeed still remains intricate 

 which the future alone can explain. Two essentially 

 different points have to be distinguished. The Heath 

 plants occur on dry, sunny, sandy plains; they extend 

 from the Cape of Good Hope, through Africa, Europe, 

 and northern Asia, to the extreme limits of vegetation in 

 Scandinavia and Siberia ; these plants are distributed in 

 this great region in such a manner that South Africa has 

 innumerable distinct species, of which, however, never more 

 than a few individuals grow side by side, that then, towards 

 the north, the number of species suddenly diminishes in 

 an important degree while the number of individuals 

 increases, till at last, in the north of Europe, a single 

 species, the common Heather,* overspreads whole countries 

 in millions of single individuals. In the first place, we 

 readily see that only the first determination, that of the 

 occurrence, relates necessarily to each individual ; while, on 

 the contrary, the range of extension, and the mode of 

 distribution indicate causes which have scarcely any 

 importance in reference to the single individual, but very 

 great in relation to the larger groups of plants, which we 

 call species, genus, tribe, &c. From this it follows that 

 the former only, the occurrence of plants, is related wholly, 

 while the other two are related but partly to conditions 

 explicable by physical influence ; yet we must, at first, 

 keep more to that arrangement, since it is strictly logical, 

 which will remain fixed for incalculably long time, while, of 

 course, the last arrangement only holds good for the 

 existing condition of Science. When namely, we review 

 the various influences upon which the life and healthy vege- 

 tation of a plant, are, according to our present physiological 



* Calluna vulgaris. 



