KNOWLEDGE OF THE MUTATING OENOTHEEAS. 23 



three were mixed indiscriminately they would form a perfectly continuous series, hoth 

 as regards width of blade and breadth of leaf-tip. In other words, the three series of 

 leaves clearly overlap in the ordinary range of their variability, for they were not 

 selected from extreme individuals but from representative members of each type of 

 mature rosette. Yet it is equally clear that this is not really a case of continuous 

 variation, for 0. laevifolia produces narrower leaves than ever occur in 0. Lamarckiana, 

 and 0. hrevisti/lis contains leaves with broader, more obtuse tips than ever occur in 

 0. Lamarchiana. But of much more importance is the fact that the modal condition for 

 wadth of leaf and breadth of tip is different for each species. Shull (1907, p. 22) has 

 shown statistically that the modal condition of O. Lamarcliiana and 0. ruhrinervis shows 

 constant differences for several characters. 



It is true that there is a certain amount of individual variability within each race — for 

 example, the leaves of the mature rosette will be, on the average, narrower in certain 

 individuals than in others ; but it is not often that all the leaves of a rosette are of such 

 character that the plant cannot be determined with reasonable certainty at this stage, 

 although occasional cases of transgressive variability occur between most of the forms, 

 which render the determination of such individuals indecisive until a later stage of their 

 development. Such cases occur in which, for instance, rosettes of 0. laemfoUa or 

 O. ruhrinervis or O. hrevistylis cannot be distinguished from O. Lamar chiana^ or vice 

 versa. But it must be said that such cases are not common. That each of these forms 

 has a different modal condition for its various leaf- characters is perfectly clear and 

 indisputable, even though transgressive variability or fluctuation occasionally asserts 

 itself with regard to any of these characters in particular individuals. 



PL 1. figs. 7 and 8 are photographs of adult plants of 0. LainarcUana, showing the 

 range of variability in the crinkling of the leaves. The individual in fig. 7 has an 

 exceptional amount of crinkling, this feature being almost as fully developed as in 

 O. lata, though the leaves are longer and more pointed than in that mutant. Pig. 8 

 marks the other extreme, in which the upper stem-leaves are practically devoid of 

 crinkling. This is much nearer the modal condition of 0. LamarcMana than the 

 previous figure, for the upper stem-leaves usually have very little crinkling. 



These figures give a fair idea of the range of fluctuating variability in cultures of 

 O. LamarcMana derived from seeds of DeVries. I have since had experience with races 

 of Oenothera from other sources, which, although they are undoubtedly to be included in 

 the species O. LamarcMana in the strictest sense, yet differ quantitatively in nearly 

 every character from the 0. LamarcMana race of DeVries's cultures, even when grown 

 side by side with them under the same environmental conditions for several generations *. 

 A study of certain of these races, and a comparison of their characters through several 

 generations with those of the O. Lamarcklana of DeVries's cultures, shows that such 

 quantitative differences, however they may have arisen, continue to be transmitted, so 

 that the races remain strictly differtjntiated. I am inclined to believe that this fact of 

 the strict inheritance of quantitative differences in various races of the same species may 



• See also note, page 67. 



