Page:An introduction to physiological and systematical botany (1st edition).djvu/120

 90 . 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 through their opening 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 opening buds can only be attributed to the increased 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