26 MUTATIONS, VARIATIONS, AND RELATIONSHIPS OF THE OENOTHERAS. 



while that in the leaf 

 ratios was toward iden- 

 tity, as will be readily 

 seen on referring to fig. 

 6, which shows a much 

 more complete over- 

 lapping than do the 

 corresponding curves 

 for 1904. In other 

 words, since this ratio 

 was taken as a measure 

 of leaf-form, the form 

 of the leaves of 0. 

 riihrinervis in the latter 

 year was but slightly 

 different from that of 

 the parent species, ex- 

 cept in those minor 

 details which were 

 pointed out in the 

 earlier study as pre- 

 venting the ratio be- 

 tween length and 

 width from being a 

 correct measure of 

 form. The lack of 

 homologvinthe leaves 

 measured in the two^ 

 species takes away all 

 significance of these 

 facts in their bearing 

 on the question of the 

 regression of 0. rubrinervis. The constants of the several curves representing 

 the variation in leaf measurements may be compared in the following table : 



I'lG. 



5. — Comparison of leaf -width of Oenotheralamarckiana (broken curve) 

 and O. rubrinervis. 



Variation in length of leaf: 



Oenothera lamarckiana 



Oenothera riihrinervis 



Variation in width of leaf: 



(Oenothera lamarckiana 



Oenothera rubrinervis 



Variation in the ratio between width and 

 length: 



Oenothera lamarckiana 



Oenothera rubrinervis 



Mean. 



Millimeters. 

 88.91 ±0.35 

 70.96 ±0.24 



36.56 ±0.091 

 27-3o±o.o79 



Per cent. 

 42.27 ±0. 10 

 39-34 ±0.13 



Standard 

 deviation. 



Millimeters. 



18.41 ±0.25 



1 1 .42 ±0.17 



4. 796 ±0.064 

 3.687 ±0.056 



Per cent. 

 5.411 ±0.072 

 5.888 ±0.089 



Coefficient 

 of variation. 



Per cent. 

 20.71 ±0.29 



16. IO±0.24 

 13. I2±0. 18 



i3-50±o.2i 



1 2 . 80 ± o . 1 7 

 i4-97±o.23 



