40 



MUTANTS AND HYBRIDS OF THE OENOTHERAS. 



Although such a character as this is too largely influenced by the 

 individual physiological vigor to be of any value as a diagnostic char- 

 acter, the difference of aspect between the lots of plants of these two 

 species was so striking that it was thought interesting to give it quan- 

 titative expression. A comparison of the number of lateral branches 

 shows complete discontinuity between the two species in this regard, 

 the range in 0. lamarckiana being from n to 25, and in O. rubrinervis 

 from 34 to 62. Curves of equal area representing the variation in the 

 number of branches of 17 specimens of O. rubrinervis and of 20 speci- 

 mens of O. lamarckiana selected by lot, are shown in fig. 4. The 

 constants of these curves are as follows : 



M 



ean. 



Standard deviation. 



Coefficient of variability. 



Onagra lamarckiana. 

 Onagra rubrinervis . . 



Meters. 



20.70 0.49 

 42.35 1.04 



Meters. 



3.24 0.35 

 6.34 0.73 



Per cent. 



15.7 1.7 

 15.0 1.7 



If, instead of the number of branches, we consider the total branch- 

 length, the results are in some respects more striking still, for in gen- 

 eral the branches are longer in O. rubrinervis than in O. lamarckiana. 

 This did not prove invariably true, however, and the discontinuity 

 which should have been increased by this difference in average length 

 is lost through the occurrence of a specimen of 0. rubrinervis having 

 a total branch-length of only 7.79 meters, though it had 39 branches. 

 This is well within the range of total branch-length of 0. lamarckiana, 

 which varied in this respect between 3.65 meters and 8.41 meters. 

 The greatest length of branches observed in any specimen of 0. rubri- 

 nervis was 29.98 meters. The variability in regard to total branch 

 length is presented graphically in fig. 5. The constants of these 

 curves are as follows : 



Onagra lamarckiana. 

 Onagra rubrinervis . . . 



Me 



Meters. 



6.68 0.20 

 18.19 1.30? 



Standard deviation. 



Meters. 



1.35 0.14 

 7.95 ,0.92 



Coefficient of variability. 



Per cent. 



20.2 2.2 

 43.7 5.1 



This comparison shows a remarkable difference throughout, the 

 most important feature probably being the fact that the coefficient of 

 variability in total branch-length is more than twice as great in 0. 

 rubrinervis as in O. lamarckiana. 



The size and shape of the leaves of Onagra .rubrinervis, Much 

 more important taxonomically than stature and branching are the 

 leaf-characters, and it is just here that statistical study encounters the 

 most serious obstacles in seeking a satisfactory basis. In the first 



