THE VEGETABLE WORLD. 303 



Wiirtemberg. Man also unintentionally gives the first 

 impulse to such wanderings, which the plant then inde- 

 pendantly continues. Thus has the Sweet-flag spread all 

 over Europe, which was originally brought from India and 

 raised in some Botanic Gardens. The Indian Fig and the 

 American Agave have, in running wild, essentially changed 

 the physiognomy of the landscape in southern Spain, Italy 

 and Sicily. In the middle of the 17th century a seed 

 of Erigeron canadense came to Europe in a stuffed 

 bird, was sown, and the plant is now distributed 

 throughout Europe, in places to which it has never been 

 conveyed by Man. The structure of seeds and fruits 

 which facilitates their being driven far and wide by the 

 wind, the voracity of birds, which devour the indigestible 

 seeds, then afterwards often germinating far distant from 

 the mother-plants in the excrement of the bird, and 

 similar circumstances, explain this free distribution of 

 plants. 



Incomparably more important however than all these 

 changes in small and individual matters, are the climatal 

 alterations which Time or the operations of Man, call forth 

 upon the earth and in the vegetable world. We know 

 truly, that the sum of the heat which our earth has 

 received for thousands of years, has not altered in a suf- 

 ficient degree to produce the smallest change in the 

 vegetable world, but the distribution of heat over the 

 globe, and in different seasons, may become essentially 

 changed in the course of time, and thus transform the 

 whole physiognomy of a country. The unhappy Iceland, 

 a few centuries ago still shared the culture of grain, which 

 now has wholly ceased, or is confined to a sterile, and in 

 most years failing crop of Barley ; the Birch, in earlier 

 periods forming dense woods, is now stunted to a low 



