44 



MUTANTS AND HYBRIDS OF THE OENOTHERAS. 



The constants of these curves, which represent the variations of 

 the two populations, each taken as a whole, are as follows: 



Considering the great variability of leaves, it would not be 

 expected that two species so closely related would exhibit complete 

 discontinuity in size of leaf or in the ratio between width and length. 

 It is not so much the extreme types of leaves which give to a plant its 

 characteristic appearance and appeal to the systematist, as the type to 

 which the majority of the leaves belong. The mean values of the 

 various leaf-characters for each individual would much more nearly 

 represent the conditions as seen by the descriptive botanist. For this 

 reason it seemed important to compare the means of length, width, 

 and form of leaves in the individual plants of the two species. The 

 results are represented in figs. 9, 10, and u, and show that there is 

 approximate identity in the mean length of the leaf, but complete dis- 

 continuity in both mean widths and the mean ratios of width to length. 

 The constants were not determined for these curves, as an inspection 

 of the curves together with a statement of the ranges will sufficiently 

 indicate the nature and degree of discontinuity present. 



The ranges of mean values of the leaf-characters in the individ- 

 ual plants were as follows : 



It will be noted that the break between the mean values of leaf- 

 width and that between the mean ratios of width to length are slight 

 but sufficient. If a larger number of specimens had been used the 

 range would have been extended somewhat and it is not improbable 

 that they would overlap some, and yet the unsatisfactory character of 



