MUTATIONS, VARIATIONS, AND RELATIONSHIPS OF THE OENOTHERAS. 25 



the leaves of that species and those of its no 

 parent of Httle value except as a demonstra- 

 tion of the difiticulties which were to be '°^ 



overcome. It seemed fair in the former year 



100 



to consider the basal branches of these two 

 species homologous, and leaves for the study 95 

 in 1904, being taken from about the middle 

 of those branches, were consequently as 9° 

 nearly comparable as possible. In 1905 the 

 leaves of O. lamarckiana were again taken 

 from the middle of the basal branches and 

 are thus comparable with those of 1904, 

 but in O. rubrinervis the leaves were taken 

 from the middle of the lowest branches pres- 

 ent, and as these were not quite basal, the 

 leaves were not homologous with those of 

 O. lamarckiana. The first striking result 

 of this lack of homology is seen in fig. 4, 

 where the variation in leaf-lengths is com- 

 pared. The corresponding curves for 1904 

 showed almost exact identity in the length 

 of the leaves, while in this figure it is seen 

 that the length of most of the 0. rubri- 

 nervis leaves corresponded in 1905 with the 

 lower part of the range of 0. lamarckiana. 

 When figure 5, representing the variation in 

 leaf-width, is compared with the corres- 

 ponding figure for 1904 it is seen that with 

 respect to this character the lack of homol- 

 ogy has had but little modifying effect, 

 and there is close resemblance between the 

 sets of curves representing the variation in 

 leaf-width for the two years, though both 

 species show a slight increase in the coef- 

 ficient of variability. The considerable 

 difference in respect to leaf-length, taken 

 in conjunction with essential identity in 

 leaf -width in 1905, has the effect to change 

 the ratios between length and width in 

 about the same degree as the change in 



length, but in the opposite direction. Thus F^g. 4— Comparison of leaf -length of O^no- 

 ,, , . , , . . , .^ thera laniarckiana {hro^en curve) anii O. 



the change m length was away from identity, rubrinervis. 



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