364 DARWINISM TO-DAY. 



tions and bundles this into the germ-plasma. It is, of course, no 

 objection to the theory that it leaves something under the heavens to 

 be accounted for. This is rather to be regarded as one of its chief 

 virtues. As working naturalists we have reason to be most sus- 

 picious of the theories that explain everything" (Wheeler, pp. 539- 

 540). 



"In view of the amount of orderly and well-authenticated evi- 

 dence now at hand, it may be regarded as demonstrated that char- 

 acters, of appreciable physiological value, originate, appear in new 

 combinations or become latent, in hereditary series of organisms, 

 in such a manner as to constitute distinct breaks in descent" (Mac- 

 Dougal, p. 540). 



23 Some of de Vries's experiments and observations on the La- 

 marck primrose have been repeated (with naturally some variation) 

 in the New York Botanic Garden, by MacDougal and assistants. 

 See MacDougal, D. T., "Mutation in Plants," Amer. Nat., VoL 

 XXXVII, pp. 737-770, 1003; also, "Mutants and Hybrids of the 

 CEnotheras," by D. T. MacDougal, assisted by A. M. Vail, 

 G. H. Shull, and J. K. Small, Pub. No. 24, Carnegie Inst. of Wash., 

 1005. 



I am aware of the rather sweeping statements made by some 

 biologists touching the probability of the origin by mutation of many 

 species, or at least, races of animals and plants. For example, 

 Castle (Science, N. S., Vol. XXI, p. 522, 1905) says: "So far, 

 however, as these various sorts of evidence go, they indicate that 

 the material used by breeders for the formation of new breeds con- 

 sists almost exclusively of mutations." And Davenport (Science, 

 N. S., Vol. XXII, p. 372, 1905) says: "Undoubtedly many, if not 

 most, of the characteristics of the races of domesticated animals and 

 probably feral species have arisen by mutation." He then refers, 

 as example, to the qualities that differentiate the races of poultry 

 feathered feet, rose comb, elongated tail, taillessness, silky 

 feathers, frizzled feathers, cerebral hernia, polydactyl feet, albinism, 

 and many others. But I have been assured by Luther Burbank, 

 the most experienced and distinguished plant breeder in this country, 

 that the many races of plants actually produced by him have not 

 been derived from mutations. But on the contrary, that the selec- 

 tion of small variations a special abundance and variety of these 

 variations usually being induced by hybridisation and by change of 

 environment has been his almost exclusively relied-on means for 

 producing new forms of plants. As a matter of fact the cases 

 actually adduced by upholders of the de Vriesian theory as supports 

 for it are astonishingly few. Castle (Science, N. S., Vol. XXI, pp. 

 522-523, 1905) calls attention to the sudden appearance of a super- 



