GENERAL SUMMARY. 



FROM MIRBEL'S VIEWS OF VEGETABLE NATURE. 



The food by which plants are nourished, and the 

 agents by which their growth is promoted, have been 

 examined in a former chapter.* To pursue the opera- 

 tion of these causes united, and to exhibit a compre- 

 hensive view of the influence of climate and soil on 

 vegetation, requires the aid of extensive observation, 

 and a knowledge of the productions of different coun- 

 tries. The forms of vegetables are extremely various, 

 and certain tribes are attached exclusively to different 

 countries. Some species are confined to the narrow- 

 est limits. The Origanum Tournefortii, discovered by 

 Tournefort in 1700, in the little island of Amorgos, up- 

 on one rock only, was found eighty years afterwards by 

 Sibthorp, on the same island, and upon the same rock ; 

 but no one has ever observed it any where else. Two 

 of the Orchidece, grow upon the Table Mountain at the 

 Cape of Good Hope ; and Thunberg, who has described 

 them, found them on no other spot. 



Mountainous countries afford many of these local 

 species ; such as dwell secluded on the heights, without 

 ever migrating to the plains below. Thus we find that 

 the Pyrenees, the Alps, and the Appenines, have their 

 peculiar Floras, and that even some separate mountains 

 of those great chains have species allotted to them alone , 

 and which are not to be found on the adjoining sum- 

 mits. 



Speculatively we might presume that all the individ- 



* Pase 39. 



