CHAP, vii.] DISTRIBUTION OF PLANTS. 197 



the impracticability of changing sides, but to the dif- 

 ferent climatal conditions usually present on the opposite 

 sides of a mountain range, depending on the relative 

 amount of heat and moisture present. Most fruits and 

 seeds quickly perish when immersed in sea-water ; the 

 fruit of the cocoa-nut is, however, an exception to this 

 rule, not suffering by prolonged immersion, and is fre- 

 quently carried for long distances by ocean currents, and 

 on being stranded under favourable conditions of tem- 

 perature, germinates at once ; by this means coral islands 

 often receive their first stock of palm trees. 



The gradual adaptation of plants to particular condi- 

 tions, determined mostly by the relative amount of heat, 

 moisture, and light, has resulted in what is termed the 

 geographical distribution of plants, or the predominance 

 of certain plants in particular areas at the present day. 

 From geological evidence, as will be shown later on, the 

 areas that at the present day are characterized by certain 

 plants, were during earlier geological periods clothed 

 with vegetation which at the present time is only to be 

 met with in widely distant regions. This change is due 

 to the altered climatic conditions that certain areas have 

 undergone from time to time. A brief account of the 

 influence of climate and geographical changes on the 

 flora of a district may be to some extent realized from 

 a brief sketch of the compulsory migrations and whole- 

 sale destruction of consecutive floras that have from 

 time to time clothed the area known as Great Britain at 

 the present day. 



The ancient flora, consisting chiefly of Cryptogams 

 and Gymnosperms, as Zamias and Cycads, that occupied 

 the site of what is now England must have been com- 



