2 



DB. E. E. GATES— CONTEIBUTION TO A 



"be referred to incidentally, the main purpose being tlie presentation of certain results of 

 studies in variation and hybridization with tbese forms, and a discussion of their general 

 bearing on our view-point with regard to the mutation problem in Oenothera. 



I may say at the outset that my purpose has been to study these mutation phenomena 

 from as many points of view as possible, in the belief that all the data from every 

 source could finally be brought together and applied in the explanation of the 

 evolutionary signi^cance of this type of behaviour. The greater the amount of 

 information already at hand with regard to any group of forms, the wider is the basis 

 of interpretation for all additional facts, and I have therefore felt that more could be 

 gained by attempting to consider a single group of organisms from every angle than by 

 studying forms belonging to many genera from any given point of view — e. g., that of 

 cytology or hybridization. This is my apology for continuing to devote my attention to 

 one somewhat limited group. I believe this intensive method is a valuable one, and in 

 the present state of oiu' knowledge is to be recommended for other genera as well. 



I have therefore studied the Oenotheras, not only as regards their cytology, but in 

 the details of their external characters, their variability, and hereditary behaviour. 

 This has involved also a study of the history of the mutating and related species in 

 cultivation, and as naturalized in Europe and other parts of the world; as well as 

 numerous cultures of wild forms from many parts of the North American continent, to 

 determine the relationships and distribution of the many geographic races. The 

 results are of course very incomplete, and even fragmentary, but I think the method is 

 amply justified by certain results already obtained : for example, the way in which the 

 cytological structure of O. gigas and its peculiar behaviour in crossing are of mutual 

 help in explaining each other; and the manner in which cultures of certain wild forms 

 of 0. muricata from Canada have thrown light on the probable origin and significance 

 of the twin types in certain hybrids of O. Lamar ckiana. 



The large quantity of data with regard to the mutating Oenotheras which has 

 accumulated since the publication of ' Die Mutationstheorie ' by DeVries (1901-3) has 

 led to a number of modifications of the views expressed by the author of that 

 monumental work with reference to the mutation phenomena which he first described. 



Subsequent studies of Oenothera Lamarchiana by MacDougal (1903, 1905, 1907), 

 myself, and others have confirmed in a general way the accuracy of DeVries's 

 observations concerning the hereditary behaviour of this species. The general facts 

 regarding the sudden, occasional, discontinuous origin of aberrant types which breed 

 true have been amply confirmed. But there remains the all-important question of the 

 evolutionary significance of this and similar behaviour. Tor an adequate interpretation 

 of these phenomena, much fuller data in a variety of directions were required. Some 

 of these data have now been supplied, and have thrown new light on the nature and 

 meaning of the process. 



A more detailed discussion of the mutation phenomena in Oenothera Lamarchiana 

 will be taken up in later sections of this paper. In this introductory statement it will 

 be well to view the mutation theory in certain of its broader aspects, and to ask what 



