120 LIFE IN NATURE. 



Several instances of the result of external forces in 

 modifying the forms of plants and animals have been 

 collected by Mr. Spencer.* The following is one of 

 his examples : 



" If we examine a common fir-tree and I choose 

 a fir-tree, because the regularity in its mode of growth 

 makes the law more than usually manifest we shall 

 find that the uppermost branches, which grew out of 

 the leading shoot, have radially arranged branchlets 

 (i. e. growing equally on all sides), and each of them 

 repeats on a smaller scale the type of the tree itself. 

 But if we examine branches lower and lower down 

 the tree, we find the vertically growing branchlets 

 bear a less and less ratio to the horizontally growing 

 ones. Shaded and confined by those above them, 

 these eldest branches develop their offshoots in those 

 directions where there are most space and light; 

 becoming finally quite flattened and fan-shaped. The 

 like general truth is readily traceable in other trees." 



In this connection, it is impossible to omit a 

 reference also to the beautiful experiments by which 



* In the British and Foreign Medico-Chirurgical Review for 

 January, 1859. 



