96 THE AMERICAN NATURALIST [Vol. LI 



factor imitations with the more complex type of behavior 

 included under the second and third categories. 



When the second category is considered we are met 

 with the task of harmonizing a large mass of rather con- 

 fusing data, and it is perhaps true that this can not be 

 done successfully at the present stage of our knowledge. 

 There are not lacking, however, as many others have 

 pointed out, a number of significant facts which are at 

 least as logically explainable on the basis of hybridity as 

 on assumptions of general germinal changes. If the re- 

 sults which have followed species crosses are to be ex- 

 tended to the ijipe of behavior displayed by Lamarchiana, 

 then it is clear that the numerical ratio in which segrega- 

 tion occurs is of no particular significance except in so far 

 as its constancy indicates that it is due to a specific be- 

 ha\4or in gametogenesis. Lotsy (1912) in particular has 

 pointed out that in Antirrhinum species crosses, races 

 may be secured which behave very much like some forms 

 of (Enothera with respect to the segregation ratios ob- 

 tained. The significant facts with which we have to deal 

 are apparently, first that in (Enothera these "mutations" 

 affect the sum total of the characters of the individuals, 

 i. e., they are dependent on complex germinal differences 

 when compared with the parents, and second that these 

 ''mutations" continually recur within certain races in 

 fairly constant ratios. These are facts which are just as 

 simply explained on the basis of a complex type of segre- 

 gacion in which many of the systems formed contain dis- 

 cordant elements and therefore fail to develop as to refer 

 them to actual change in germinal substance. Moreover, 

 the former explanation harmonizes the results obtained 

 with the simpler category of strictly Mendelian phe- 

 nomena. 



That this view of the (Enothera situation has something 

 in its favor beyond the known general occurrence of par- 

 tial sterility in this genus is shown by some of the results 

 of hybridization between the various forms of (Enothera. 

 The frequent appearance of populations consisting of 

 distinct forms is usually taken to be an expression of 



