rgis.] PURE SPECIES OF (ENOTHERA. 19 



experimental studies in the group. On the assumption of specific 

 purity the Mutationists rest their conclusions. This condition with 

 respect to the characters studied is also basic to Mendelian experi- 

 mentation. It need scarcely 'be emphasized that no species of 

 CEnothera has as yet passed the tests for genetic purity outlined 

 above and that consequently we have at present no standard material 

 with which forms may confidently be mated in the test of cross- 

 breeding. It should become the concern of CEnothera geneticists 

 to find and isolate pure material as the starting point of further 

 studies in experimental morphology. Whether such pure forms 

 will be found among the wild species or as products of the garden 

 time will determine. 



University of Pennsylvania, 

 May, 1915. 



LITERATURE CITED. 

 Atkinson, G. F. 



1914. Segregation of Unit Characters in the Zygote of CEnothera with 

 Twin and Triplet Hybrids in the First Generation. Science, XXXIX., 



834 1914- 

 Bartlett, H. H. 

 igisa. Additional Evidence of Mutation in CEnothera. Bot. Gaz., LIX., 



81, 1915. 

 1915b. The Mutations of CEnothera stenomeres. Amer. Jour. Bot., II., 



100, 1915. 

 igiSc. Mutation en masse. Amer. Nat., XLIX., 129, 1915. 

 Davis, B. M. 



1911. Some Hybrids of CEnothera biennis and O. grandiflora that Resem- 

 ble 0. Lamarckiana. Amer. Nat., XLV., 193, 191 1. 



1912. Further Hybrids of CEnothera biennis and O. grandiflora that Re- 

 semble 0. Lamarckiana. Amer. Nat., XLVL, 377, 1912. 



1913. The Behavior of Hybrids between CEnothera biennis and 0. grandi- 

 flora in the Second and Third Generations. Amer. Nat., XLVIL, 



447, 1913- 



1914. Some Reciprocal Crosses of CEnothera. Zeits. ind. Abstam. u. 

 Vererb., XII., 169, 1914. 



1915a. Professor De Vries on the Probable Origin of CEnothera Lamarck- 

 iana. Amer. Nat., XLIX., 59, 1915. 

 1915b. A Method of Obtaining Complete Germination of Seeds in 

 CEnothera and of Recording the Residue of Sterile Seed-like Struc- 

 tures. Proc. Nat. Acad. Sci, I., 360, I9I5. 

 De Vries, Hugo. 

 1907. On Twin Hybrids. Bot. Gas., XLIV., 401, 1907. 

 1909. On Triple Hybrids. Bot. Gaz., XLVIL, i, 1909. 



