ORGANIC EVOLUTION 289 



germinated, there would appear among the seedlings a few that were 

 very different from the others. These few being brought under culti- 

 vation developed into individuals with all the marks of species distinct 

 from the parent. Moreover, they " came true," generation after gen- 

 eration, which is regarded as the final test of a species. In this way 

 O. Lamarckiana was observed to give rise to several new species, in 

 some cases the same species appearing repeatedly. Not all of these 

 suddenly produced species would have survived in nature, but some of 

 them had already stood this test in the vacant field. This immediate 

 appearance of a fully equipped new species, without any intermediate 

 stages or any building up by selection, DeVries called mutation, the 

 forms thus produced being mutants. The role of natural selection in 

 this case is not to produce species, but to select among those already 

 produced. It is evident that a mutant is simply a large variation, such 

 as are called "sports." 



DeVries investigated the results of plant breeders, as Darwin had 

 done, and distinguished between improved forms and really new forms. 

 The former evidently arose from the continuous selection of small varia- 

 tions, and were always inconstant. The very few new forms produced 

 were constant, and, so far as records of their pedigree were available, 

 were found to have arisen in each case from some individual that had 

 suddenly appeared among the cultures. In other words, new forms 

 were found, not produced; and when found, they remained constant. 

 Naturally DeVries concluded that all the new and permanent forms that 

 have appeared in connection with plant breeding have been mutants, 

 and have not been built up by continuous selection. 



It is entirely unknown whether this mutating condition is of general 

 occurrence. Cultures of plants and animals are being carried on by 

 numerous investigators, and the results may indicate presently whether 

 mutation is to be regarded as a general method in the origin of species 

 or as only an occasional one. It is becoming more and more evident 

 that new species may have arisen in several ways, perhaps including all 

 the methods heretofore suggested, and certainly including some that 

 remain to be discovered. Whether mutation stands or falls as an 

 explanation of evolution, the most important contribution of DeVries to 

 evolutionary science is its transfer from the field of observation and 

 comparison to the field of experimental work. 



Orthogenesis. — Natural selection utilizes small variations in building 

 up new species, and mutation calls large variations species. In both 



C. B. & C. BOTANY — 19 



