352 LESSONS FROM NATURE. [CHAP. XL 



of a definite kind, is to contradict the plain evidence of our 

 senses and our reason. 



&quot; This internal principle it is which produces the character 

 of each tree s growth, while the special details are determined 

 by the action of external influences upon it. Just in the 

 same way, I believe, that an innate predisposing cause pro- 

 daces the evolution of new species ; the special details being 

 determined by subordinate agencies, and amongst them that 

 of Natural Selection. Mr. Wright s illustration suits me so 

 well I will pursue it yet further. He observes : 



&quot; If we could study the past and present forms of life, not only in 

 different continents, which we may compare to different individual 

 trees of the same kind, or better, perhaps, to different main branches 

 from the same trunk and roots, but could also study the past and 

 present forms of life in different planets, then diversities in the general 

 outlines would probably be seen similar to those which distinguish dif 

 ferent kinds of trees, as the oak, the elm, and the pine ; dependent, as 

 in these trees, on differences in the physical and physiological properties 

 of living matters in the different planets supposing the planets, of 

 course, to be capable of sustaining life, like the earth, or, at least, to 

 have been so at some period in the history of the solar system. 



&quot; Precisely so once more ! In each case forms would be 

 evolved in accordance with that innate potentiality which 

 God has implanted in each case in the matter of which such 

 planet was composed. Not that there, any more than here, 

 all that was potential would become actual, but that the 

 innate potentiality, modified by external influences, would be 

 determined in special forms in the production of which the 

 innate power, not the external conditions, would be the main 

 evolving agent. 



&quot; Mr. Wright seems to consider that the use of such words 

 vitaiforcos as P^ arit y an d luminosity tends to discourage 

 the investigation of the laws and conditions by and 

 through which such properties are manifested. Mr. Wright 

 tells us somewhat dogmatically that definite vital aggrega 

 tions and definite actions of vital forces exist, for the most 

 part, in a world by themselves. I should be the last to 

 deny the distinctness of vitality, but that certain con- 



