FOKCIXG OF PLANTS. .. 69 



viojus. The vegetables of cold climates, on the con- 

 trary, support a much greater degree of cold wkhout 

 injury, at least while in a torpid state ; for when their 

 buds begin to expand tliey become vastly rnore sen- 

 sible, 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 through their opening buds. It must pene- 

 trate equally through them in the course of long and 

 severe winter frosts, which are never known to injure 

 them. The extremely pernicious effects th.erefore of 

 cold on opening buds can only be attributed to the in- 

 creased susceptibility 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 forcing them, and 

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

 health, under a colder sky than is natural to them. 

 But many alpine plants, naturally buried for months 

 under a deep snow, are not only extremely impatient 

 of sharp frosts,, but will not bear the least portion of 

 artificial heat. The pretty Primula marginata, Curt. 

 Mag. t. J 91, if brought into a room with a fire when 

 beginning to blossom, never opens another bud ; while 

 the American cowslip, Dockcathcon Alcadia, t, 12, 

 one of the most hardy of plants with respect to cold, 

 bears forcing admirably w^ell. 



Mr. Knight very satisfactorily shows, Phil. Trans, 

 for 1801, 343, that plants acquire habits with regard 



