Varietäten, Descendenz, Hybriden. 5 



parisons between observed and expected series has made it impös- 

 sibie to determine the degree of the supposed approximalions. 

 Yule's coefficient of association is proposed as a criterion of com- 

 parison , and to make possible the determination of probable errors. 



In several cases correlations have been found to be reversible, 

 dependinc^ on the way the characters were combined in the parents. 

 This fact has further complicated the theory of gametic coupling, 

 niaking it necessar}^ to assume that characters which at one time 

 attract each other, at others exhibit repulsion. 



In hybrids between Chinese and American varieties of maize 

 coherence has been found between the texture of the endosperm 

 and the color of the aleurone layer. In a few cases, the degree of 

 the correlation approached very closely to that expected from a 

 gametic coupling in a 3:1 ratio. 



Correlations were found in crosses of the Mendelian form Aa 

 bb X aa bB. Such correlations are held to indicate that in some 

 cases at least, the correlation between the characters must be de- 

 termined after the formation of the gametes. 



On the other hand, correlations resulting from crosses of the 

 form AaBbX^abb eliminate the possibility of selective poUination 

 as a general cause of correlations. 



The general conclusion is reached that associations between 

 characters, like the appearance of Single characters, may rise at 

 different stages in the ontogenj^ of the individual. Jongmans. 



Davenport, B, C, Light thrown by the experimental study 

 of heredity upon the factors and methods of Evolu- 

 tion. (American Naturalist. XL VI. p. 129—138. 1912.) 



Modern experimental study of heredity has given a new for- 

 mulation to the problem of evolution and has given definite data 

 on the method of evolution. It formulates the problem of evolution 

 as the problem of the nature and origin of the germinal determi- 

 ners of characters. It has shown that, for the most part, the new 

 determiners arise one at a time and are independent of one another, 

 raav occur in any combination and may be transferred from one 

 strain or species to another. It has been shown that the unit cha- 

 racters are much more numerous and (iner things than we had 

 thought and, therefore, that the Steps of evolution are frequently 

 very smair ones and are taking place in many directions. It has 

 shown the relative unimportance of the isolation factor, since true 

 blends of characters rarely, if ever, occur. It has demonstrated the 

 lack of influence b}^ soma upon germ-plasm; but has rendered it 

 probable that external conditions may directly modify the determi- 

 ners of the germ-plasma. It brings support for the view of selective 

 elimination of undiserable traits but finds that many, if not most, 

 characters that arise are neutral in respect to any adaptive signi- 

 ficance. Finally, it looks forward with a justifiable expectancy to 

 the completer experimental test of the factors of evolution and their 

 eventual complete elucidation. Jongmans. , 



East, E. M. and H. K. Hayes. A genetic analysis ofthe 

 changes produced by selection in experiments with 

 Tobacco. (American Naturalist. XLVIII. p. 1—48. 9 Fig. 1914.) 



There can be no doubt that the original „Halladay" type of 



