FUNCTIONAL VARIATION 103 



by both species, the one above the other. This dam broke, 

 mixing the two species, but in three years original conditions 

 were practically restored. The experiments were undertaken 

 to learn whether real transformation had taken place or whether 

 the result had been brought about by selection. 



The experiment seems convincing, and the point is further 

 strengthened by the facts that Schmankewitsch restored the 

 caudal fins by reducing the solution, and that when the reduction 

 was carried below the normal of A. salina, within three genera- 

 tions the last segment of the body divided after the fashion of 

 A. bmnchipus, another related species. The facts are the more 

 remarkable as A. salina reproduces parthenogenetically, while 

 A. branchipus is not known to do so. 



Biologists are extremely careful not to assume the absolute con- 

 version of one species into another by any such direct methods 

 as have here been noted, the question being, rather, whether they 

 are all good species ; but that single characters are profoundly 

 influenced by changed conditions, and come to resemble the same 

 character in another and related species, is too well established 

 to be longer questioned. What light this may finally throw upon 

 the origin of species is problematical, but it serves the present 

 purpose in showing the power of environment to profoundly 

 modify the functional activities of living beings. 



If a cutting of willow, currant, or other suitable growth be 

 planted in the earth, roots will start from the part below the 

 ground, and leaves and branches from the part above. If, now, 

 it be cut off at the surface of the ground and the top portion be 

 planted again, it will again take root at the new point of sever- 

 ance which had before borne leaves. The process may be con- 

 tinued indefinitely, or until the piece is used up, showing that 

 roots or leaves may be developed at will at any point along the 

 cutting, according as it is placed below or above ground. 



If a cutting be planted, roots will develop only at the lower end. 

 If, however, before planting it be cut into two pieces, each will 

 develop roots on the part below ground, and in many species this 

 will occur even if the pieces be inverted and planted top down. 1 



1 This is most likely to take place in young wood, less likely in old wood. See 

 Morgan, Regeneration, pp. 71-91. 



