ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 197 



Upon the retreat of the ice-sheet, that portion of the continent north 

 of the terminal moraine was tenanted again by plants migrating north- 

 wards which were adapted to a cold temperate climate. Many of these 

 came from the southern Appalachians, where they had remained un- 

 disturbed during the long Ice Age ; these mountains served as a centre of 

 distribution from which a considerable area in the south-eastern states 

 was populated. A study of the principles underlying the distribution of 

 plants in eastern America, shows the great antiquity of the flora of the 

 mountains of western North Carolina. The presence of so many peculiar 

 types of plants not found elsewhere in America, and having their closest 

 relations in eastern Asia, makes it more certain that groups now broken 

 up and detached were once continuous, and that fragmentary groups and 

 isolated forms are but the relics of widespread types, which have been 

 preserved in a few localities where the physical conditions were especially 

 favourable, or where organic competition was less severe. Evidence of 

 this antiquity is found in western North Carolina in the large size of the 

 trees, the close commingling in a dense forest of a great variety of 

 species, the graded-down appearance of the land surface, and the rounded 

 contour of the mountains, all suggesting that the country has been sub- 

 jected through long ages to the continued action of climatic forces. 

 The deep soil in the North Carolina mountains, rich in organic detritus, 

 points to the long occupation of the territory by dense forests, the most 

 magnificent (excepting those of the Pacific slope) to be found anywhere in 

 the Western Hemisphere. 



The characteristic features of the vegetation are found in the broad- 

 leaved species of which it is largely composed, associated with deciduous- 

 and evergreen shrubs, while lianes stretch from tree to tree, and herbs 

 grow beneath the dominant forest species, or clothe the natural meadows 

 of the higher mountain summits and the alluvial bottoms of the prin- 

 cipal mountain streams. The association of these plants in the forest is 

 due largely to their relation to light, soil and moisture. Ecologically, the 

 following formations may be distinguished : 



1. Mixed deciduous forest formation, 2000-5000 ft. 



2. Coniferous forest formation, 5000-G700 ft. 



3. Sub-alpine dwarf tree-shrub formation, about G000 ft. 



4. Sub-alpine treeless formation, above 6000 ft. 



Polar Climate in Time the Major, Factor in Evolution.* — Gr. R„ 

 Wieland, as a result of the study of the facts of distribution, concludes 

 that climatic changes of a character affecting life must in the course of 

 time be of minimum amount at the equator, and increase towards the 

 poles, where the maximum amount of such change occurs. Hence the 

 nearer a given locality to either pole, the greater the seasonal vicissitudes 

 to which its life is subjected. The origin of life probably took place at 

 the north, or both the poles, though the possibility of a supplementary 

 or extra-terrestrial origin requires consideration. The Palaeozoic period, 

 from climatic and other reasons — such as freer circulation of oceanic 

 waters, and the greater number of aquatic animals, and lowly organised 

 or spore-bearing plants — must have been one mainly of generalised 



* Amer. Journ. Sci., xvi.|(1903) pp. 401-30. 



