4S6 BOTANICAL GAZETTE [December 



2. The phenomenon is known in two species of Oenothera: O. 

 Reynoldsii, in which it was iirst described, and O. pratincola, the 

 subject of this paper. 



3. It cannot be explained by Heribert-Nilsson's Mendelian 

 hypothesis. 



4. The mutations of the mass mutant strain of O. pratincola are: 



(A) common to other strains of the species; the non-characteristic 

 mutations are not produced in unexpected numbers and show mass 

 mutability superposed upon their ordinary behavior in heredity; 



(B) characteristic of the mass mutant strain. 



5. The characteristic mutations are constant in that they do 

 not throw the type form of the species, but, except in the case of 

 the most reduced member of the group, are themselves highly 

 mutable. 



6. As far as tested, the characteristic mutations adhere to the 

 following scheme of inheritance: 



mutation X mutation -> mutation 

 mutation X parent -> mutation 

 parentXmutation-> parent 



7. They belong to a group with certain structural characters 

 in common, but do not seem to form a linear reduction series. 



8. They seem to result from the mutative modification in the 

 female gametes of factors which have no counterparts in the male 

 gametes. 



9. Mass mutation is associated with a high degree of sterility, 

 which manifests itself in the production of a greatly reduced number 

 of seeds or in the production of many empty seeds. 



University of Michigan 



