132 THE AMERICAN NATURALIST [Vol. XLIX 



There can therefore be no doubt that the F 2 was an essen- 

 tially uniform generation and that the F 3 was the first 

 generation to throw the two dwarf types, except perhaps 

 as rare mutations, which were not detected on account 

 of the small size of the cultures. In this connection it 

 may be remarked that the mutations of Oenothera Rey- 

 noldsii can not be detected in very young cultures with 

 any degree of precision. Up to the time the rosettes are 

 set out in the garden, after they have been started in the 

 greenhouse in pots, they show no consistent differences 

 among themselves. It happens that six seedlings of the 

 1913 F 3 were photographed before any diversity what- 

 ever had been detected in the culture. They must there- 

 fore be considered a random sample from the 26 plants. 

 All turned out to be mut. semialta except one, which was 

 f. typica* The photograph is reproduced as Fig. 2. 

 At maturity the contrast between the classes is very 



