66 CALIFORNIA ACADEMY OF SCIENCES. 



mism'^ ^ * ^ " that growth-force, uninfluenced by 

 inherited peculiarity, or any stronger influence locating 

 a nutritive fluid, must develop extent in the direction of 

 least resistance, and density on the side of greatest resist- 

 ance, when not too great. The illustration of this state- 

 ment would be that of a globular mass of cells brought 

 to the point of junction of two media, as water and 

 earth or air and earth, elongates in the direction of the 

 medium presenting the least resistance, i.e., air." This 

 law may be further illustrated by the growth of the 

 foliage of a tree. When a tree is located in the midst 

 of a forest, it is crowded on all sides and accordingly 

 expends its energy in growing upward. If, on the 

 other hand, a barrier be placed to its upward growth, 

 the foliage will become dense and matted at the point of 

 obstruction. This law of extent and density, as enun- 

 ciated by Prof. Cope, is apparently intended to account 

 for the distribution of force in individuals or species 

 only, but it seems to me possible that a broader inter- 

 pretation may be put upon it than Prof. Cope had in- 

 tended to imply. As an analogy representing the dif- 

 ferentiation of life the structure of a tree has been com- 

 monly used, the spreading branches of which illustrate 

 the divergent course of life through past geologic ages, 

 while the leaves and terminal buds constitute the life 

 of to-day. But the analogy of the tree may serve an- 

 other purpose. It has been stated that the growth of a 

 tree is conditioned by Cope's law of extent and density. 

 This is a law of ontogony. But just as the perfect tree 

 represents the direction of organic progress, so the law 

 of growth force which conditions the growth of the tree, 

 conditions also the growth of organic beings as a whole. 

 In other words, life as a whole has made progress or 



* Origin of the Fittest, p. 30. 



