112 FACTORS OF EVOLUTION 



times in a mutable and at times in an immutable condition, the 

 latter state being very much the more prevalent. Indeed so 

 prevalent is the immutable condition among plants that only a 

 small proportion of the species embraced in the flora of any given 

 region may be found existing in their mutable period. Further- 

 more, it has been found, and was to be expected, that some plants, 

 even when in the fulness of their mutable period, would exhibit 

 their mutability more readily than others,' 



At the conclusion of an address delivered last year before the 

 University of Chicago, which the author has kindly sent me. Prof, 

 de Vries said : — " Mutability is manifestly an exceptional state 

 of things if compared with the ordinary constancy. But it must 

 occur in nature here and there, and probably even in our own 

 immediate vicinity. It has only to be sought for, and as soon 

 as this is done on a sufficiently large scale the study of the origin 

 of species will become an experimental science." 



All that is said in the last two paragraphs will subsequently be 

 found to be just as applicable to Heterogenesis as it occurs among 

 lower forms of life, except that the resulting transformations are 

 then much more radical and complete than are those resulting 

 from ' Mutation.' In these latter changes, when occurring in 

 higher plants, each newly originated species, while possessing 

 distinctly separate attributes, is never, as de Vries intimates, very 

 widely different from the parent form. 



The contrast between the two processes above referred to and 

 those of Natural Selection is great in all ways, seeing that the 

 latter never admits of actual proof and observation, depending, 

 as it does, or is commonly believed to do, upon the progressive 

 accumulation of most minute useful variations along a particular 

 line, through generation after generation, so that it leads not to 

 random or purposeless features, but always to " ceaseless adapta- 

 tions of the species to its life-conditions." The time needed for 

 the production of all the forms of life that have ever lived by 

 a process so essentially slow as this would surely be prodigious, 

 and must inevitably far exceed anything that geologists would 

 demand — not to speak of the far narrower limits which physicists 

 are wilUng to assign for the age of our globe, dating from the 

 consolidation and cooling of its surface. 



" This account of the views of de Vries is derived from an interesting paper by 

 Charles A. White, in "The Smithsonian Report" for 1901, pp. 631-640. 



