SECTION III. THE ARCTIC ZONE 



CHAPTER I 



GENERAL CHARACTERS OF 



THE ARCTIC CLIMATE AND ITS EFFECTS ON 



VEGETATION AND FLORA 



I. General Characters of the Arctic Climate. General features. Summer tempera- 

 tures. Difference between the temperature of the air and that of objects exposed 

 to insolation. Atmospheric precipitations. Meteorological tables. 2. Effects of the 

 Arctic Climate on Plant-life. i. Survey of the Climatic Factors, ii. Vegetative 

 Season and Periodic Phenomena. Conditions of existence of plants in the arctic regions 

 according to Kjellman. Awakening of vegetation from its winter sleep. Middendorff's 

 observations. Ripening of fruits, iii. Growth and Metabolism 0/ the Vegetative Organs. 

 Stunted growth. Growth under continuous and interrupted illumination. Assimilation 

 in continuous sunlight. Histological peculiarities caused by continuous illumination, 

 iv. Xerophilous Structure of the Vegetative Organs. Xerophilous features caused by the 

 coldness of the ground. Cushion-growth, v. Reproductive Organs. Wealth of blossoms. 

 Relatively large dimensions of the flowers, vi. Reputed Protective Measures against Cold. 

 3. The Floristic Character of the Arctic Zone. The flora of Greenland according to 

 Warming. The flora of Spitzbergen according to Nathorst. 



i. GENERAL CHARACTERS OF THE ARCTIC CLIMATE. 



Of the two polar zones of the earth, the southern is stated to be entirely 

 without vegetation. This assumption will perhaps be disproved by later 

 observations. In any case the antarctic polar zone is at present beyond our 

 ken as regards phytogeographical considerations. On the other hand, the 

 arctic polar countries, so far as they are free from ice in summer, support 

 a poor and stunted vegetation everywhere beyond the tree-limit. 



The limit of tree-growth oecologically forms the natural southern 

 boundary of the district of arctic vegetation. It lies in some places to the 

 north, and in others to the south of the polar circle, the former being the 

 case in Europe and Asia, and the latter in America ; it reaches its northern- 

 most position at some points in Siberia, and its southernmost in Labrador. 



Temperature and illumination constitute the chief characteristics of the 

 polar climate, the former in the long cold winter and the short cool summer, 

 the latter in the long winter night and the long summer day. The darkness 

 of winter has no effect on plant-life, at least on terra firma. Moreover, the 



