24 BOARD OF AGRICULTURE. 



of course, from the profuse vegetation of the tropics to the 

 stunted forms of the polar regions and the alpine tops of 

 high mountains. In North America a great belt of forest 

 extends down the Pacific coast from Alaska to California, 

 across to Newfoundland, and thence south to the Gulf of 

 Mexico. The treeless regions are the coast of California 

 below the thirty-fifth degree of latitude, the plains and prai- 

 ries east and south-west of the Rocky Mountains, and the 

 great arid deserts which occupy that vast region which lies 

 south of the Blue Mountains of Oregon and between the hioh 

 Sierras and the Rocky Mountains, extending far south into 

 Mexico, and which is known as the " Great Basin." This 

 interior dry region is caused by the westerly winds blowing 

 from the Pacific Ocean, and the southerly and easterly winds 

 blowing from the Gulf of Mexico, depositing their moisture 

 on the intervening mountains, which shut it in from the in- 

 fluence of the ocean. This is not the time, nor will space 

 permit us, to give even an outline of the theories Avhich 

 are advanced to account for the present distribution of 

 forest-trees. For countless generations, species have been 

 slowl}' adapting themselves to their fitting places. Natural 

 selection, and the survival of the fittest forms for the posi- 

 tion they are to occupy, have placed on the earth's surface 

 the exact species in the exact positions best suited for tlieir 

 development. In different climates and in different situa- 

 tions the particular variety, too, of the species that can best 

 sustain the local conditions to which it must be subjected, is 

 found. This is illustrated very clearly by some of our own 

 forest-trees. The most widely distributed of North-Ameri- 

 can coniferse, and one little changed in appearance, is the red 

 cedar (^Juniperus Vir(jiniana). This tree is found as far north 

 as latitude fifty, and south to the Gulf of Mexico, extending 

 from the Atlantic to the Pacific. At its extreme northern 

 limit it is only a shrub ; on our own sterile hills it becomes 

 a rugged tree, and is of no little economic value for many 

 purposes ; while in the warmer climates of Florida the same 

 species is banished to the SAvamps, and furnishes that clear, 

 soft wood used the world over in the manufacture of the 

 best lead pencils. The Douglas spruce, which is one of the 

 most valuable of American forest-trees, has a less extended 

 range. It is common from British Columbia to Mexico, ex- 



