28 THE PRESENT. 



from which peculiar families have emanated to perform their 

 functions in the great economy of nature. 



I. ITS FLORA OR PLANT-LIFE. 



Glancing first at the VEGETABLE WORLD, we perceive that 

 the great regulators of plant-life are heat, light, and mois- 

 ture. Such is the order of nature now, and such, we are 

 bound to believe, have been the ordainings of creation from 

 the earliest moment that the vegetable cell was evoked into 

 existence. Under the tropics, both individual exuberance 

 and specific variety attain their maximum intensity ; in the 

 temperate zones this intensity gradually declines ; while in 

 the arctic regions vegetable life dwarfs and diminishes till 

 it ultimately disappears and gives place to utter sterility. 

 As we start from the equator, each great belt equatorial, 

 tropical, subtropical, warm-temperate, cold-temperate, sub- 

 arctic, arctic, and polar* presents its own distinctive fea- 

 tures ; and though the zones of the southern hemisphere 

 may differ in genera and species from those of the northern, 

 there is still in the respective stages a sufficient resemblance 

 of growth, colouring, and inflorescence, to prove that, lati- 

 tude for latitude, the prime governing influence is essenti- 

 ally solar. As with latitude, which is influenced in the 

 main by light and heat, so with height above the level of 

 the ocean an advance upwards into the rarer regions of 

 the atmosphere being equivalent, in some measure, to an 

 advance northwards or southwards into the colder latitudes 



* The equatorial zone extends on both sides of the equator to about 

 15 of latitude ; the tropical from 15 to the tropics ; the subtropical 

 from the tropics to 34" ; the warmer temperate from 34 to 45 ; the 

 colder temperate from 45 to 58 ; the subarctic from 58 to the polar 

 circle ; the arctic from the polar circle to latitude 72 ; and the polar 

 zone from 72 to the poles. 



