LUTHER BURBANK'S WORK 363 



SCIENTIFIC ASPECTS OF LUTHER BURBANK'S WORK 



By VERNON L. KELLOGG 



PROFESSOR OF ENTOMOLOGY, STANFORD UNIVERSITY 



IV iT R. BURBANK has so far not formulated any new or additional 

 -*-'-*- laws of species-change, nor do his observations and results 

 justify any such formulation, and we may rest in the belief that he 

 has no new fundamental laws to reveal. He has indeed the right to 

 formulate, if he cares to, some valuable and significant special con- 

 clusions touching certain already recognized evolution factors, in par- 

 ticular, the influence on variability of the two long-known variation- 

 producing factors of hybridization and modification of environment. 

 His reliance on the marked increase in variability to be got after 

 a crossing in the second and third generations over that obvious 

 in the first will come as a surprise to most men first getting acquainted 

 with his work. He has got more starts for his new things from these 

 generations than in any other way. He is wholly clear and convinced 

 in his own mind as to the inheritance of acquired characters ; ' acquired 

 characters are inherited or I know nothing of plant life/ he says ; and 

 also convinced that the only unit in organic nature is the individual, 

 not the species; that the so-called species are wholly mutable and de- 

 pendent for their apparent fixity solely on the length of time through 

 which their so-called phyletic characters have been ontogenetically 

 repeated. He does not agree at all with de Vries that mutations in 

 plants occur only at certain periodic times in the history of the species, 

 but rather that, if they occur at all, they do so whenever the special 

 stimulus derived from unusual nutrition or general environment can 

 be brought to bear on them. He finds in his breeding work no prepo- 

 tency of either sex as such in inheritance, though any character or 

 group of characters may be prepotent in either sex. He believes that 

 no sharp line can be drawn between the fluctuating or so-called Dar- 

 winian variations and those less usual, large, discontinuous ones called 

 sports. Ordinary fluctuating variation goes on under ordinary condi- 

 tions of nutrition, but with extraordinary environmental conditions 

 come about extraordinary variation results, namely, discontinuous, sport 

 or mutational variation. These variations are the effects of past en- 

 vironment also, having remained latent until opportunity for their 

 development occurs. Starvation causes reversions, but reversions can 

 also be produced by unusually rich nutrition. New variations are de- 

 veloped most often, as far as environmental influences go, by rich soil 



