No. 507] BOTANICAL SOCIETY OF AMERICA 145 



habitants of the various regions can be wholly accounted 

 for by climatal or other physical conditions," (2) " bar- 

 riers of any kind or obstacles to free migration, are re- 

 lated in a close and important manner to the differences 

 between the productions of various regions," (3) "the 

 affinity of the productions of the same continent, or of the 

 same area, though the species themselves are distinct at 

 different points and stations." 2 These scarcely need 

 comment, for they arise clearly from the law of origin by 

 descent. They are such an intrinsic part of the founda- 

 tion of plant geography as to require an effort to recog- 

 nize the fact that it was once necessary to formulate them. 



Single and Multiple Origin 

 From the very nature of his task, Darwin was forced 

 to assume that species were first produced at one spot. 

 To-day the fact that the same species may arise at two 

 or more distinct places merely strengthens the law of 

 descent, but in Darwin's time this would have greatly 

 increased the difficulty of supporting his doctrine by the 

 evidence drawn from the distribution of plants. Dar- 

 win's views upon this question were far from uncertain, 

 as the following excerpt indicates. 



It is obvious that the individuals of the same species, though now 

 inhabiting distant and isolated regions, must have proceeded from 

 one spot, where their parents were first produced. We are thus brought 

 to the question which has been largely discussed by naturalists, namely, 

 whether species have been created at one or more points of the earth s 

 surface. Undoubtedly there are many cases of extreme .litlimlty m 

 understanding how the same species could possibly have migrated trom 

 some one point to the several distant and isolated points where now 

 found. Nevertheless, the simplicity of the view that each species was 

 first produced within a single region captivates the mind. He who 

 rejects it, rejects the vera causa of ordinary generation with subsequent 

 migration, and calls in the agency of a miracle. 3 



This view seems to be little more than an inheritance 

 from the special creationists. It doubtless reflects the 

 prevailing opinion of Darwin's time, and probably is m 



2 "Origin," 2: 129. 



