REPORT OF EXECUTIVE COMMITTEE. 47 



the same way seems quite undeniable ; and as soon as the validity 

 of this generalization is granted for these cases it will have to be 

 considered of general, if not universal, bearing. 



It is chiefly owing to the work of Mr. MacDougal that the evening 

 primroses have come to be recognized in America as the true material 

 for the stud}^ of evolution by sudden leaps. His cultures of the 

 original stock and some of its mutants have proven the significance 

 of the differences between the new and the old species, and have 

 awakened an increasing interest in this line of research. To the 

 demands made by such work the laboratory has to respond, and it 

 is now mj' duty to point out the chief lines which should be followed 

 in order to reach this aim. 



Two main lines have to be distinguished : the study of the phe- 

 nomenon itself and that of its causes. Mutations, of course, can 

 not be assumed to be a special feature of the evening primroses. 

 They must occur elsewhere, too, and these have to be sought for. 

 The Oenothera was one of a lot of nearly a hundred species tested 

 as to their constancy ; it proved to be the only changeable form 

 among them. By testing a hundred other species or other strains 

 of the same forms it seems probable that one or two new instances 

 of mutability may be detected. The best way is to tr}- the wild species 

 of the nearest environments or of other regions with a corresponding 

 climate, since large numbers of seedlings have to be examined. One 

 or two novelties among thousands of individuals of the common 

 type are not easih' found, especially when the differences are slight 

 and new, and thereby apt to be overlooked. Much care is to be 

 given, and the trials have to be repeated with the same species in 

 succeeding years. With increasing experience the chances of dis- 

 cerning the small indications of novelties are rapidly augmented. 

 No differentiating marks, however slight, should be considered as 

 insignificant. All aberrant individuals should be planted separately 

 and protected with all the care required to insure the fullest devel- 

 opment. Many of them afterwards prove to be only fluctuating 

 variants or to have deceived the experimenter. They are simply 

 discarded. It is quite sufficient if some remain and prove to be 

 mutants. As soon as in this manner a mutable strain will be dis- 

 covered the greater part of the other species may be excluded, 

 although the search for new mutable species should never be wholly 

 neglected. Each year some new forms should be taken into cul- 

 ture, in order to have sufficient chances of gradually increasing the 

 evidence concerning the occurrence of mutability in nature. 

 5 



