4 DAVIS— THE TEST OF A [April 23. 



existence, and probably is a form of comparatively recent origin. 

 De Vries ('15, p. 173) has asserted again most vigorously his belief 

 that Lamarckiana may be identified with a specimen from the United 

 States collected by Michaux and now in the collections of the 

 Museum d'Histoire Naturelle in Paris (De Vries, '14). With this 

 view I cannot accord for reasons recently published (Davis, '150). 

 The showing of " mutants " from (Enothera biennis can hardly be 

 considered very encouraging for the mutation theory of organic 

 evolution when it is remembered that biennis semi-gigas is self 

 sterile, that biennis nanella is frequently weakly or diseased, and 

 that biennis sulfurea is clearly a retrogressive type having lost the 

 power of producing normal yellow flowers. 



Although O. biennis of all the Oenotheras brought into the ex- 

 perimental garden still seems to me the form most free from sus- 

 picion of gametic impurity, nevertheless the line of Stomps has not, 

 so far as we know, been subjected to the tests of a pure species sum- 

 marized at the conclusion of this paper. De Vries ('15, p. 173) is 

 mistaken in quoting me as conceding for this species a pure origin. 

 I regard it simply as the safest material yet known on which to 

 conduct studies in mutation, and with which other forms may be 

 crossed to determine by the constitution of the F^ hybrid genera- 

 tion whether or not their gametes are uniform. If in such a breed- 

 ing test the Fj progeny fall into two or more classes the assump- 

 tion is justified that the form crossed with biennis must produce 

 different classes of gametes. If the Fj hybrid generation is uniform 

 then it is clear that the functioning gametes male and female are 

 respectively uniform. The fact that Lamarckiana crossed with 

 biennis produces the " twin hybrids " laeta and velutina is, as has 

 frequently been pointed out, one of the most important facts favor- 

 ing the hybrid nature of Lamarckiana. It seems to me not improb- 

 able that other species of CEnothera will eventually be isolated more 

 stable than the Dutch biennis. 



Some exceedingly interesting observations have recently been 

 reported by Bartlett ('15 a, b, c) on the behavior of certain small- 

 flowered, self-pollinated American Oenotheras. When grown in 

 selfed lines these forms exhibit a behavior similar to that of 

 Lamarckiana and biennis in throwing off in successive generations 



