130 EXCITABILITY OF PLANTS. 



cepts are necessary. There, too, famine and epidemics occur less fre- 

 quently and the fluctuations of trade and the revulsions of productive 

 industry are least felt. The introduction and cultivation of a single 

 seed often sways the destiny of whole nations, and may change the 

 aspect of the whole world. The potato, rice, cotton, and a blade of 

 wheat are examples in point of the effects produced by vegetable pro- 

 ducts and cultivation. And when we see that a seed not larger than 

 a pin's head is elaborated by nature, within a brief season, into a 

 flourishing root twenty millions of times larger than its present grain, 

 we cannot be insensible to the arts of culture, the principles of nature, 

 or the power and wisdom of the benificent Author. 



Some plants, it will be seen, are evidently destined to render the 

 earth cheerful and beautiful, and others are distinguished by their 

 great utility as food for man and beast, while a very great number are 

 both useful and beautiful. Trees are such as to afford us hard wood, 

 as the oak, apple, and elm, and many others afford soft wood, as wil- 

 low, poplar, etc., while others afford us gums and resing, as pines, fir, 

 etc. The hard wood is best for fuel, giving out the greatest heat, as 

 it has the most carbon, while resinous woods burn most freely from 

 the greater quantity of hydrogen which they contain. 



Not only are the differences in vegetable products admirably calcu- 

 lated both for the support and gratification of our physical nature, but 

 those of different climates and. countries have an important influence 

 on the moral and social condition of man. This is perceived in the 

 study of natural history, the discovery of new and valuable produc- 

 tions, the extension of commerce and the establishment of colonies ; 

 thus extending the comforts, the arts and literature and the general 

 prosperity of whole nations. The desire to possess the different pro- 

 ducts of different countries stimulates alike the merchant and the 

 traveler ; and the introduction thereby of a few new seeds has essen- 

 tially changed the condition of the people of large and populous 

 countries. Almost all of the most valuable vegetables have thus been 

 introduced from other countries. It is by marking these facts and 

 reflecting upon the attendant circumstances that we become impressed 

 with the importance of our subject. 





