1917] DeVRIES— OENOTHERA 15 



It seems probable that the increased breadth and the dimin- 

 ished bubbles of the higher leaves of the stem and of the bracts of 

 the inflorescence are expressions of a single change, which must 

 consist in a thorough stretching of the blade parallel to its surface. 

 If this be so, we may conclude that the bubbles, which are so 

 characteristic of O. Lamarckiana, are due to some deficiency in this 

 stretching and thereby constitute a recessive character. If this 

 conclusion be granted, the smoothness of the leaves of O. blandina 

 must be dominant in its crosses with 0. Lamarckiana, and in this 

 way be transferred to both of its twins, causing the one to be a laeta 

 instead of a pure Lamarckiana. We are thereby provided with 

 a beginning of an experimental analysis of the marks of mut. 

 velutina, as already discussed. 



Here I might insert some considerations concerning the mutative 

 origin of O. blandina. We have seen that 0. Lamarckiana and 

 O. nanella, when crossed with this new form, repeat its characters 

 in part of the offspring. In the same way a mutant velutina may 

 be produced by the conjugation of a mutated sexual cell with 

 a normal one. Thus it is not necessary to assume the accidental 

 meeting of two mutated gametes, which would obviously make the 

 chance of the mutation occurring very much smaller still. It is 

 sufficient to suppose that only the female elements of the original 

 O. laeta have mutated in this way, although we cannot know whether 

 this change might not have taken place in the male cells. And 

 since O. blandina behaves as an isogamous species, both hypotheses 

 seem to be equally probable. In both cases mutants of the laeta 

 type should be expected to appear also, but as they would be very 

 rare and not discernible in the beginning from the Lamarckiana 

 specimens which always develop out of a part of the seeds of 0. lata, 

 they would surely have been overlooked in the years 190 7- 1908, 

 when the mutation into blandina occurred. 



I shall now give a more detailed description of my experiments. 

 The crosses were made in 19 13 and the first generation was culti- 

 vated twice for every cross, once in 19 14 and once in 191 5. 



O. blandinaXO. Lamarckiana. — A biennial specimen of the 

 latter form was chosen and its pollen placed on the stigma of two 

 individuals of the thoroughly green type of 0. blandina. The seeds 

 of one cross were sown in 19 14, and those of the other in 191 5. 



