THE MUTATION THEORY 355 



biennial culture for the other. Rubrinervis may be annual in appar- 

 ently all specimens, in sunny seasons, which would allow a large 

 part of the gigas to remain in the state of rosettes during the entire 

 first summer. It would be very interesting to obtain a fuller insight 

 into the relation of the length of life to other qualities, but as yet 

 the facts can only be detailed as they stand. 



Both of these stout species have been found quite constant from 

 the very first moment of their appearance. I have cultivated them 

 from seed in large numbers, and they have never reverted to the 

 lamarckiana. From this they have inherited the mutability or the 

 capacity of producing in their turn new mutants. But they seem to 

 have done so incompletely, changing in the direction of more absolute 

 constancy. This was especially observed in the case of rubrinervis, 

 which is not of such rare occurrence as 0. gigas, and which it has been 

 possible to study in large numbers of individuals. So for instance, 

 "the red-veins" have never produced any dwarfs, notwithstanding 

 they are produced very often by the parent-type. And in crossing 

 experiments the red-veins gave proof of the absence of a mutative 

 capacity for their production. 



[Besides the mutants just described there occurred two weak forms 

 that could survive only if reared under protection and would have 

 failed to survive in nature. Here we have a place for the action of 

 natural selection, but operating with mutations instead of with 

 fluctuating variations. These two mutants are " the whitish and the 

 oblong-leaved evening-primroses or the Oenothera albida and oblonga." 



All of the mutants so far mentioned are constant forms that breed 

 true to type. Certain other types were either incapable of being bred 

 or else were decidedly inconstant. Oenothera lata had only pistillate 

 flowers and therefore could not be fertilized by pollen of the same 

 mutant. Oenothera scintillous and 0. clliptica are fertile to their own 

 pollen, but produce progeny only partly like the parent, the rest 

 reverting to the original type Oenothera lamarckiana. ED.] 



SUMMARY OF DE VRIES'S MUTATION THEORY 1 



THOMAS HUNT MORGAN 



We may now proceed to examine the evidence from which De 

 Vries has been led to the general conclusions given in the preceding 

 pages. De Vries found at Hilversum, near Amsterdam, a locality 



*T. H. Morgan, Evolution and Adaptation (1903). Used by special permission 

 of the publishers, The Macmillan Company. 



