LIFE OF PLANTS. 243 



cool days are interchanged with warm weather, wlience we 

 account for the luxurious vegetation of alpine regions and of 

 tropical climates, where a considerable coolness during the 

 night succeeds the heat of the day. 



371. 



It is worthy of remark, that seeds and bulbs most perfectly 

 withstand the cold, because they suffer no considerable in- 

 crease of susceptibility, by the withdrawing of the vital sti- 

 mulus during sleep. Generally, the effects of heat and cold 

 in plants must be considered in connection with the action of 

 their internal powers. As the powers of plants are connected 

 with a certain organization, no plant will accommodate itself 

 to a certain temperature, unless its organization permits this 

 change. We can transplant vegetables from foreign coimtries 

 into our own ; but we cannot, by centuries of cultivation, 

 force plants from warmer regions, to become perennial in 

 colder climates, as the common examples of Cucumbers, 

 French Beans, and Potatoes, shew. It is believed respecting 

 many plants, that by custom they become more hardy and 

 agree with our climate ; but this is a deception which proceeds 

 from our want of information respecting the nature of many 

 regions, which, on account of their latitude, we presume to be 

 very hot. It is true that we have partly accustomed to our win- 

 ter some Japanese plants from the fortieth degree of north lati- 

 tude ; but Japan contains mountains, and lies east from Asia, 

 where the temperature is always lower than in western re- 

 gions. The Japanese plants, too, are not more hardy than 

 those from the mountainous districts of America, which lie 

 under the same degree of latitude, (391 •) 



372. 

 Another very important stimulus for the whole vegetable 

 world is presented by electricity. Obscure as the science of 

 atmospherical electricity still is, we yet know with certainty that 

 the influence of electrical excitation, and the discharge of po- 

 sitive electricity, is one of the most powerful stimulants to 

 the vital action of plants. We })erceive this from storms. 



Q2 



