4f 



DE. E. E. GATES— CONTEIBUTION TO A 



of plants freely intercross. This is the condition under which their evolution takes 

 ice. If, as some think, O. Lamarclciana orisrinated in Gardens throuijli crossino* 

 between, e. g., O. grandiflora and O. biennis, then it would probably have also 

 originated long previously through crossing where these occupied the same area in 

 Eastern North America. Indeed, this conclusion is difficult to avoid, and I have 

 previously shown (Gates, 1911 a) that both 0. biennis and O. grcindijlora survived in the 

 region of Virginia and Carolina until a century ago. 



As discussed later in this paper, a Lancashire colony of Oenotheras which has existed 

 .for certainly over a century, contains O. Lamar chiana as the dominant form. Such 

 facts as these serve to show that the essential points to decide in determining the 

 status of mutation as an evolutionary factor are, (1) will O. Lamarckiana survive in 

 competition with its near relatives, and (2) will the mutants survive in competition with 

 0. Lamarckiana. The former point has already been settled affirmatively by a study of 

 the Lancashire colony already mentioned. The only actual evidence yet obtained for 

 the latter is the fact that DeVries found certain forms, such as the putative mutants 

 O. brevistylis and. 0. laevifolla, persisting year after year with 0. Lamarckiana, in the 

 field at Hilversum near Amsterdam where they were originally found. Competition 

 experiments will be required before it can be known which of the mutants will survive 

 under various climatic conditions. 



DeVries has emphasized the fact that certain of the mutants seem to differ in their 



physiological adjustments or adaptations; O. gigas, for instance, being more strongly 



biennial than the other forms. But the value of any such differences can only\e 



determined by actual experiments on the survival of the mutants under various climatic 

 conditions. 



The ingenious theory of DeVries, that new forms appear suddenly, already adapted to 

 various environments, and are afterwards so distributed that each reaches the environ- 

 ment for which it is most fitted, in spite of certain obvious diffi^culties 

 survival during the period of its distribution, may account for certain cases of whal we 

 may call climatic adaptation. But such a principle can scarcely be extended to the 

 more complex cases of adaptation in plants and animals which it is one of the main 

 duties of evolutionists to explain. I may quote the celebrated passage from Darwin 

 (' Origin of Species,' 6th Edition, page 2) in which he cites two such cases :— " It is pre- 

 •'posterous to attribute to mere external conditions, the structure, for instance, of the 

 " woodpecker, with its feet, tail, beak, and tongue, so admirably adapted to catch insects 

 " under the bark of trees. In the case of the mistletoe, which draws its nourishment 

 " from certam trees, which has seeds which must be transported by certain birds, and 

 ** which has flowers with separate sexes absolutely requiring the agency of certain 

 " msects to bring pollen from one flower to the other, it is equally preposterous to 



account for the structure of this parasite, with its relations to several distinct orc^anic 



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beings, by the effects of external conditions, or of habit, or of the volition of the plant 



It seemsi almost equally incredible that a series of chance mutations could account for 



