Presumptive Mutations in Wild & Cultivated Plants 55 



CHAPTER VI. 

 PRESUMPTIVE MUTATIONS IN WILD AND CULTIVATED PLANTS. 



Obviously, if the mutation theory is to be of any use the 

 conceptions derived from controlled breeding experiments must 

 be applicable to plant and animal species and varieties as they 

 occur in nature. A beginning has only been made in this vast field 

 of application, but it is sufficient to show that the mutationist 

 conception of germinal changes is widely applicable to the variations 

 observed among wild species. As an aid in the analysis of the 

 populations that go to make up a wild speoies it is undoubtedly of 

 great service, and its illuminating influence is also beginning to 

 make itself felt in the fields of systematics, phylogeny and relation- 

 ships. Innumerable records of species, varieties and forms in the 

 literature of systematic botany and zoology and the journals of 

 naturalists show how universal is the incidence of this principle. 



That the relationships and origin of nearly related species can 

 also in many cases be most clearly interpreted in terms of unit 

 differences has been shown by Bateson (1913) for the North 

 American warblers (Helmintbophila) and flickers (Colaptes) and 

 other forms. In plants, the same principle has been applied (Gates, 

 1916) to species of Spiranthes, Clintonia, Streptopus, Maianthemum, 

 Ranunculus, Actaeaand Spiraea, and in a preliminary way to he genus 

 Trillium (Gates, 1917b). Similar analytical conceptions have been 

 applied to the differentiation of species and varieties, their relation- 

 ships and phylogeny, in the North American Melanthaceae (Gates, 

 1918a) and Convallariacea; (Gates, 1918b). The results are in no 

 sense revolutionary, but wherever the mutational principles are 

 applicable they do appear to give a more clear-cut and accurate 

 analysis of specific differences, and also of the phylogenetic and 

 distributional relationships within a group. Moreover, there is the 

 beginning of a physiological element in classification on these 

 principles, which is a distinct gain. More recently Small (1917-19) 

 has successfully applied these principles to a study of the develop- 

 ment of the Composite, though obviously his present results are 

 mainly tentative. 



It is obvious that in older groups, and wherever extinction has 

 taken place, the actual succession of mutations in the development 

 of any group will be obscured or lost altogether. These principles 

 can be most readily and widely applied to modern expanding groups 



