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THE AMEBIC AN NATURALIST [Vol. XLIX 



of degrees of sterility both gametic and zygotic, and the consid- 

 eration of whether such sterility is genetic or physiological. 

 From such tests it is possible to reach much clearer conclusions on 

 the genetic purity of (Enothera material than has been possible 

 in the past. 



Finally reference should be made to the important confirmation 

 by De Vries 6 of the studies of Stomps on (Enothera biennis L. 

 In large cultures totaling 8,500 plants from Stomps 's selfed line 

 De Vries obtained 8 plants of a dwarf biennis nanella about 0.1 

 per cent., 4 plants of biennis semigigas (21 chromosomes) about 

 0.05 per cent., and 27 plants of the color variety biennis sulfurea 

 about 0.3 per cent. Since the percentages from Lamarckiana 

 are for nanella 1-2 per cent, and for semigigas 3 per cent., it 

 would appear that biennis is the more stable of the two species, 

 although the color variety biennis sulfurea is a new type in 

 experimental studies in (Enothera. A culture of over 1,000 

 plants from selfed seed of biennis sulfurea, all with pale yellow 

 flowers, produced 2 dwarfs, thus giving what De Vries calls a 

 ' ' double mutant, ' ' O. biennis mut. sulfurea mut. nanella. 



This behavior of (Enothera biennis is to the writer much more 

 trustworthy evidence for mutation than that presented from the 

 studies on Lamarckiana since biennis has a record of a long 

 history as a species on the sand hills of Holland, where there ap- 

 pears to have been little probability of recent contamination. 

 However, the showing of "mutants" from biennis does not ap- 

 pear very encouraging for the mutation theory of organic evolu- 

 tion when it is remembered that biennis nanella is frequently 

 weakly or diseased, that biennis semigigas is self sterile, and that 

 biennis sulfurea appeal's to be a retrogressive form having lost the 

 power of producing normal yellow flowers. Although the Dutch 

 biennis of all the Oenotheras so far brought into the experimental 

 garden still seems to me the form most free from suspicion of 

 genetic impurity, nevertheless, the line of Stomps 's has not, so 

 far as we know, been subjected to all of the tests of a pure species. 

 Until these tests are made it is not safe to assume that this mate- 

 rial is wholly pure. It seems to mo not improbable that other 

 species of (Enothera will eventually be isolated more stable than 

 the Dutch biennis. Bradley Moore Davis 



June, 1915 



eDe Vries, Hugo, "The Coefficient of Mutation in (Enothera biennis L.," 

 Sot. Gaz., Vol. LIX, p. 169, 1915. 



