146 



NATURE 



[J tine 15, 1882 



the far more numerous cases where there is no discover- 

 able similarity of physical conditions, and of their not 

 occurring in places where the conditions are similar. 

 Now under the theory of modification of species after 

 migration and isolation, their representation in distant 

 localities is only a question of time, and changed physical 

 conditions. In fact, as Mr. Darwin well sums up, all the 

 leading facts of distribution are clearly explicable under 

 this theory ; such as the multiplication of new forms, the 

 importance of barriers in forming and separating zoo- 

 logical and botanical provinces ; the concentration of 

 related species in the same area ; the linking together 

 under different latitudes of the inhabitants of the plains 

 and mountains, of the forests, marshes, and deserts, and 

 the linking of these with the extinct beings which formerly 

 inhabited 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 in the 

 botanical field he would have left an indelible mark on the 

 progress of botanical science. But the consideration of 

 the various questions which the problem of the Origin of 

 Species presented 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 

 commences : — 



" The view generally entertained by naturalists is that 

 species, when intercrossed, have been specially endowed 

 with the quality of sterility, in or.der to prevent the con- 

 fusion 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 embodied in his well- 

 known papers on dimorphic and trimorphic plants afforded 

 an absolutely conclusive proof that sterility was not in- 

 separably tied up with specific divergence. But the 

 question is handled in the most judicial way, and when 

 the reader of the chapter on hybridism arrives at the con- 

 cluding words in which Mr. Darwin 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. Darwin's method to follow 

 up on its own account, as completely as possible, when 

 opportunity presented, any side issue which had been 

 raised apparently incidentally in other discussions. In- 

 deed it was never possible 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 was this 

 practice of bringing out from time to time the contents of 

 his unseen treasure-house which affords some insight into 

 the scientific energy of his later years, at first sight so in- 

 explicably prolific. Many of his works published during 

 that period may be properly regarded in the light of ex- 

 cursuses on particular points of his great theory. The 

 researches on the sexual phenomena of heterostyled 

 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 deve- 

 lopment in the volume " On the Different Forms of 

 Flowers or 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 dif- 



ferentiated, favours the vigour and fertility of their off- 

 spring," finds its complete expansion in " The Effects of 

 Cross and Self-Fertilisation 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 firi'cis of a vast accumula- 

 tion of facts and arguments which the author had col- 

 lected. It was intended to be but the precursor of a 

 series of works in which all the evidence was to be 

 methodically set out and discussed. Of this vast under- 

 taking only one, the " Variation of Plants and Animals 

 under Domestication " was ever actually published. Apart 

 from its primary purpose it produced a profound impres- 

 sion, especially on botanists. This was partly due to the 

 undeniable force of the argument from analogy stated in 

 a sentence in the introduction: — "Man maybe said to 

 have been trying an experiment on a gigantic 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 unexpected use of the vast body of apparently trivial 

 facts and observations which Mr. Darwin with astonish- 

 ing industry had disinterred from weekly journals and 

 ephemeral publications of all sorts and unexpectedly 

 forced into his service. Like Moliere's Monsieur Jour- 

 dain, who was delighted to find that he had been unwit- 

 tingly talking prose all his life, horticulturists who had 

 unconsciously moulded plants almost at their will at the 

 impulse of taste or profit were at once amazed and 

 charmed to find that they had been doing scientific work 

 and helping to establish a great theory. The criticism of 

 practical men, at once most tenacious and difficult to 

 meet, was disarmed ; these found themselves hoist with 

 their own petard. Nor was this all. The exclusive pro- 

 vince of science was in biological phenomena for ever 

 broken down ; every one whose avocations in life had to 

 do with the rearing or use of living things, found himself 

 a party to the " experiment on a gigantic scale," which 

 had been going on ever since the human race withdrew 

 for their own ends plants or animals from the feral and 

 brought them into the domesticated state. 



Mr. Darwin with characteristic modesty had probably 

 underrated the effect which the "Origin of Species" 

 would have as an argumentative statement of his views. 

 It probably ultimately seemed to him unnecessary to 

 submit to the labour of methodising the vast accumula- 

 tions which he had doubtless made for the second and 

 third instalments of the detailed exposition of the evi- 

 dence which he had promised. As was hinted at the 

 commencement of this article, his attention was rather 

 drawn away from the study of evidence already at the 

 disposal of those who cared to digest and weigh it to the 

 exploration of the field of nature with the new and pene- 

 trating instrument of research which he had forged. 

 Something too must be credited to the intense delight 

 which he felt in investigating the phenomena of living 

 things. But he doubtless saw that the work to be done 

 was to show how morphological and physiological com- 

 plexity found its explanation from the principle of natural 

 selection. This is the idea which is ever dominant. Thus 

 he concludes his work on climbing plants : — " It has often 

 been vaguely asserted that plants are distinguished from 

 animals by not having the powers of movement. It should 



