BOOK I 

 THE EVOLUTION OF THE PLANT- WORLD 



CHAPTER I 



THE DISTRIBUTION OF LAND AND WATER 

 IN THE PAST 



OUR earth is a somewhat irregular spheroid, the surface 

 of which is estimated at 196,940,000 square miles. Of 

 this about 142,000,000 square miles is now sea, and 

 55,000,000 land, i.e. about 71.7 per cent, of the former 

 to 28.3 per cent, of the latter; or roughly as 5 : 2. A 

 glance at the map, or, still better, at a globe, shows how 

 very unequally this land and water is at present distri- 

 buted over the surface of the globe. There is, in fact, 

 thirteen times more land north of the equator than 

 there is to the south of it. This alone must obviously 

 have a profound influence on plant-distribution the 

 vast ocean area being almost exclusively represented, 

 so far as plant life is concerned, by Diatoms and Algae; 

 very few flowering plants, such as the Grass- wracks 

 (Zoster a], inhabiting salt water. 



Though at first sight the disposition of the masses of 

 land and water on the present surface of the globe 

 appears most irregular, it will be readily perceived 

 that there is an Arctic or North Polar Ocean surrounded 

 by an almost continuous ring of land which is continued 

 in three pairs of continents that extend meridionally 

 and taper to the south. Similarly, round the land of 

 the Antarctic Continent there is a continuous belt of 

 ocean extending northwards in three oceans tapering 

 in that direction, two of them uniting in the Arctic. 

 Land and water are thus, as it has been said, " arranged 

 like a pair of interlocking cog-wheels, each with three 

 teeth." It will also be observed that the land and 

 water areas on the surface of the globe are to a very 



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