SEED SOWING 227 



boulders thus transported, and also numerous 

 plants brought from northern regions. Thus Na- 

 ture gives her children a chance to travel the wide 

 world and seek their fortunes, and acclimatise them- 

 selves, if they can, in new-found fields. 



But another mystery of the flowers appears in 

 the presence of Alpine flowers on mountain tops 

 of Europe and America, with none of their kind 

 on the intervening lowlands, yet bearing a relation 

 with the Arctic flora in regions directly north of 

 their habitat. Thus plants on isolated mountain 

 peaks of the United States and Labrador resemble 

 the Arctic plants of the Western hemisphere, and 

 those growing in Alps and Pyrenees resemble those 

 of the Eastern, and many are common to both. 

 The strange isolation and kinship of these moun- 

 tain plants is explained as follows : 



Before the Glacial Period a warmer climate pre- 

 vailed in the Northern hemisphere than at present, 

 and the temperate zone reached much farther north, 

 so that plant forms of that zone dwelt farther north 

 and peopled a part of what we now call the Arctic 

 continent, and flourished uniformly over the polar 

 regions. Then, gradually, great fields of ice and 

 snow pushed southward from the Pole and crept 

 downward from mountain peaks to verdant val- 

 leys. All tender and temperate plants decamped 



