84 FORCING OF PLANTS- 



same appearance ; which is exemplified every autumn 

 in the Garden Nasturtium, Tropceolum majus. The 

 vegetables of cold climates, on the contrary, support a 

 much greater degree of cold without injury, at least 

 while in a torpid state ; for when their buds begin to 

 expand they become vastly more sensible, as is but too 

 frequently experienced in the fickle spring of our 

 climate. Nor is this owing, as vulgarly supposed, 

 merely to the greater power of the cold to penetrate 

 th'ough their oj)ening buds. It must penetrate equally 

 through them in the course of long and severe winter 

 frosts, which are never known to injure them. The 

 extremely pernicious effects therefore of cold on open- 

 ing buds can only be attributed to the increased suscepr 

 tibility of the vital principle, after it has been revived by 

 the warmth of spring. 



The vegetation of most plants may be accelerated by 

 artificial heat, which is called yorcm^ them, and others 

 may, by the same means, be kept in tolerable health, 



ground near a volcano as hot as 210*, and at the same time cov- 

 ered with flowers. See Willdenow's Principles of Botany. 



In a similar manner the plants of high latitudes are capable of 

 withstanding intense and long continued cold. Acerbi, in his 

 travels in Sweden and Lapland, found Pines, Firs, and Birches 

 from Tornea almost to the North Cape. Mackenzie, in latitude 

 about 69, near the Frozen ocean, found the ground in July cover- 

 ed with short grass and flowers, though the earth was not thaw- 

 ed above four inches from the surface, beneath which was a solid 

 body of ice. In the island of Spitzbeigen, there grow not less 

 than thirty species of plants. In these climates, vegetation is 

 exceedingly rapid during the few months which permit it.] 



