RAPIDITY OF VEGETATION. 139 



pend upon the mean temperature of the situation 

 alone, but rather upon the prevalence of a suffi- 

 ciently mild atmosphere during a certain portion 

 of the season, there seems to be nothing ano- 

 malous in the fact, although at first it certainly 

 has the appearance of anomaly. Plants which 

 can endure considerable frost, and remain at rest 

 during the period of an arctic winter, vegetate 

 very rapidly when subjected to a mild tempera- 

 ture ; hence we find them bursting into flower 

 almost as soon as the snowy covering is removed 

 from above them, perfecting their seed, and prepar- 

 ing for a quiescent state again, all within the space 

 of a few weeks. At Melville Island I dug up 

 a plant of the Saodfraga oppositofolia in the 

 depth of winter, when the thermometer was 

 sixty-two degrees below the freezing point, and 

 brought it into the cabin, where we were raising 

 mustard and cress over the pipe of the stove. 

 In four hours it began to push, and the next 

 day it had perceptibly grown, but the want 

 of air and light, of course, prevented its coming 

 to perfection. In some sheltered situations at 

 Spitzbergen the radiation of the sun must be 

 very .powerful during about two hours on either 

 side of noon, as we have frequently seen the 

 thermometer upon the ice in the offing at fifty- 

 eight degrees, sixty-two degrees, sixty-seven de- 



