DEPARTMENT OF EXPERIMENTAL EVOLUTION. 89 



Variation and Hybridisation in Evening Primroses (Oenothera). — The 

 series of cross and self fertilized strains of Oenothera lamarckiana and cer- 

 tain of its derivatives have been continued by Dr. Shull, and special atten- 

 tion has been given to the offspring produced by several mutants from O. 

 gigas and O. rnbrincrvis. A striking variegation in which the leaves have 

 a yellowish-green central region surrounded by a dark-green margin is found 

 to be slightly inheritable. The first plant of this sort was found last year. 

 During the past season a second type of variegation has appeared, which 

 is probably closely related to that first discovered, but has the central region 

 of the leaf dark-green and the margin yellow. The latter kind of variegation 

 has appeared on three different individuals of quite independent origin, and 

 in two of the three plants the two sorts of variegation occur on different 

 portions of the same plant. It is anticipated that this second type of varie- 

 gation will differ very materially from the first in the extent to which the 

 offspring will be affected. 



Reciprocal crosses among three biotypes of Oenothera crnciata and be- 

 tween these three biotypes and O. lamarckiana have yielded a remarkable 

 series of F x hybrids, the reciprocal families being in every case unlike, and 

 many of the progenies being polymorphic. The latter consist of two or four 

 distinct types. In several of the combinations a uniform progeny results 

 when one of the biotypes is the seed-parent and a dimorphic or tetramorphic 

 progeny when the other is the seed-parent. An interpretation of these 

 anomalous results may be found only by carefully following each of the 

 hybrid types through the second and probably later generations. 



Relation between Heredity and Environment in Corn. — Dr. Shull has pro- 

 duced purebred strains of maize that vary greatly in quantity of yield. If 

 a high-producing and a low-producing strain be crossed, the second hybrid 

 generation gives offspring that show great variability in yield. Now, while 

 under good conditions and poor conditions the absolute yield is different 

 (environmental differences), under both conditions there is the same relative 

 variability in the yield among the progeny of this F 2 generation (hereditary 

 differences). 



Inheritance of Light Reaction in a Parthenogenetic Species. — The theory 

 that selection within the "pure line" is without effect should, obviously, apply 

 to parthenogenetic species. And it is important to know if it holds for 

 physiological characters as well as morphological. So Dr. Banta set himself 

 (November 191 1) to the task of testing the hypothesis that selecting within 

 a "pure line" of daphnids the most and the least sensitive to light will not 

 result in producing more or producing less light-sensitive strains. These 

 lines have now (August 31) entered from the twentieth to the twenty-third 

 generation. The material is favorable, inasmuch as the organism is prolific 

 and new generations appear in rapid succession. Under the most favorable 

 conditions a brood of young is sometimes produced by an individual when 

 only 7 days old ; and one and the same female may produce successive broods 



