LIFE AND WORKS OF DARWIN 331 



decades take heart, for it appears that while there are inborn differ- 

 ences between men in this regard, imagination, observation, reasoning 

 and production do not necessarily dim with age. Darwin's mind re- 

 mained young and plastic to the end; his latest and one of his most 

 characteristic works, " The Formation of Vegetable Mould through the 

 Action of Earth Worms " was published at the age of seventy-two, 

 after forty-four years of observation. It contained another and per- 

 haps the most extreme demonstration of Lyell's principle that vast 

 changes in nature are brought about by the slow operation of infini- 

 tesimal causes. 



Three of Darwin's succeeding volumes are a filling out of the 

 " Origin." " The Variation of Animals and Plants under Domesti- 

 cation" (2 vols., 1868) presents the entire fabric of the notes begun 

 twenty-one years before on the transmutation of species. " The 

 Descent of Man " (1871) was another logical outcome of the " Origin," 

 yet it was only faintly adumbrated by a single allusion in that work 

 to the fact that the transmutation of species necessarily led to the 

 evolution of man. The " Descent " marks tlie third of the great dates 

 in the history of thought, as the " Origin " marks the second, because 

 it is the final step in the development of ideas which began with Co- 

 pernicus in 1543. The world-wide sensation, the mighty storm pro- 

 duced by this bold climax of Darwin's work, is so fresh in the memory 

 of all that a mere allusion suffices. The evolutionary or genetic basis 

 for modern psychology as stated in " The Descent of Man " was given 

 still more concrete form in Darwin's succeeding and most delightful 

 volume "The Expression of the Emotions" (1872). 



The knowledge of zoology and anatomy displayed in these four 

 evolutionary volumes came from direct observation, vast and syste- 

 matic reading and note-taking from the simple materials which Dar- 

 win could collect at Down. Always penetrating as these observations 

 are, they are still, in my opinion, surpassed in beauty and ingenuity 

 by his marvelous work on plants, published between 1862 and 1880. 

 Here the principles of coadaptation of plants and insects in cross- and 

 self-fertilization, in climbing plants and insectivorous plants, in forms 

 of flowers, in movements of plants, are all brought forth in support of 

 the theory of natural selection and the operation of unknown laws. 

 Darwin's most precise observations and some of his most brilliant dis- 

 coveries recorded in these volumes laid the foundations of modern 

 experimental botany. 



Of his method Darwin writes : 



From my early youth I had the strongest desire to understand or explain 

 whatever I observed, that is, to group facts under some general laws. My mind 

 seems to have become a kind of machine for grinding general laws out of large 

 collections of facts. 



The only work which Darwin wrote deductively was his " Coral 



