DARWIN AND HUMBOLDT. 



[317] 13, 



extinct beings which formerly in- 

 habited the same areas ; and the fact 

 of different forms of life occurring in 

 areas having nearly the same physical 

 conditions." 



If Mr. Darwin had done no more 

 than this for botanical science he 

 would have left an indelible mark on 

 its progress. But the consideration 

 of the various questions which the 

 problem of the origin of species pre- 

 sented led him into other inquiries in 

 which the results were scarcely less 

 important. The key-note of a whole 

 series of his writings is struck by 

 the words with which the eighth 

 chapter of the Origin of Species com- 

 mences : 



"The view generally entertained 

 by naturalists is that species, when 

 intercrossed, have been specially 

 endowed with the quality of sterility, 

 in order to prevent the confusion of 

 all organic forms." 



The examination of this principle 

 necessarily obliged him to make a 

 profound study of the conditions and 

 limits of sterility. The results em- 

 bodied in his well-known papers on 

 dimorphic and trimorphic plants af- 

 forded an absolutely conclusive proof 

 that sterility was not inseparably tied 

 up with specific divergence. But the 

 question is handled in the most cau- 

 tious way, and when the reader of the 

 chapter on hybridism arrives at the 

 concluding words, in which Mr. Dak- 

 win declares that on this ground "there 

 is no fundamental distinction between 

 species and varieties," he finds himself 

 in much the same intellectual position 

 as is produced by the Q.E.D. at the 

 end of a geometrical demonstration. 



It was characteristic of Mr. Dar- 

 win's method of study to follow up on 

 its own account, as completely as pos- 

 sible, when opportunity presented, 

 any side issue which had been raised 

 apparently incidentally in other dis- 

 cussions. Indeed, it was never pos- 

 sible to guess what amount of evi- 

 dence Mr. Darwin had in reserve 

 behind the few words which marked 

 a mere step in an argument. It is 

 from his practice of bringing out from 



time to time the contents of his un- 

 seen treasure-house that we gain 

 some insight into the scientific fertil- 

 ity of his later years, at first sight so 

 inexplicably prolific. Many of his 

 works published during that period 

 may be properly regarded in the light 

 of disquisitions on particular points 

 of his great theory. The researches 

 on the sexual phenomena of hetero- 

 styled plants, alluded to above, which 

 were communicated to the Linnean 

 Society in a series of papers ranging 

 over the years 1862-8, ultimately 

 found their complete development in 

 the volume On the Different Forms 

 of Flowers on Plants of the same 

 Species, published in 1877. In the 

 same way, the statement in the Origin 

 of Species, that "the crossing of 

 forms only slightly differentiated 

 favors the vigor and fertility of 

 their offspring," finds its complete ex- 

 pansion in The Effects of Cross and 

 Self-Fertilization in the Vegetable 

 Kingdom, published in 1876. 



The Origin of Species in the form 

 in which it has become a classic in 

 scientific literature was originally only 

 intended as a preliminary precis of a 

 vast accumulation of facts and argu- 

 ments which the author had collected. 

 It was intended to be but the precur- 

 sor of a series of works in which all 

 the evidence was to be methodically 

 set out and discussed. Of this vast 

 undertaking only one portion, the 

 Variation of Plants and Animals 

 under Domestication, was ever actu- 

 ally published. Apart from its pri- 

 mary purpose it produced a profound 

 impression, especially on botanists. 

 This was partly due to the undeniable 

 force of the argument from analogy 

 stated in a sentence in the introduc- 

 tion: "Man may be said to have 

 been trying an experiment on a gigan- 

 tic scale; and it is an experiment 

 which nature, during the long lapse 

 of time, has incessantly tried." But 

 it was still more due to the unex- 

 pected use of the vast body of appar- 

 ently trivial facts and observations 

 which Mr. Darwin with astonishing 

 industry had disinterred from weekly 



