MULTIPLE FACTORS IN MENDELIAN INHERITANCE 193 



This conclusion is very similar to many of the cases cited 

 above. All of these deal with heritable characters quantitatively 

 different. They are subject, to a greater or less degree, to fluctu- 

 ations that, not being heritable, may be roughly assigned to 

 environment. Offspring from crosses between extremes are gen- 

 erally of an intermediate nature. In the following generation 

 new forms appear that are similar to the original parents or even 

 more extreme. The greater number of individuals are inter- 

 mediate. In certain cases crosses between similar lines, after a 

 first generation like the parents, give a second generation in 

 which a wide range of grades appear. These are the facts that 

 can be definitely ascertained from the work that has been done. 

 On the probability that these same phenomena will always be 

 found, a law may be stated : the second generation of a size cross 

 will show greater diversity than does the first generation or the 

 parental lines. All practical application will come from this. 



The interpretation of multiple factors can be applied to all 

 the facts. It goes hand in hand with the mutation, and pure 

 line doctrines of de Vries and Johannsen, and in its breadth of 

 application, and its comprehensive simplicity, this theory, based 

 on the assumption of the segregation of distinct units, is very 

 attractive; by its use as a working hypothesis important facts 

 have been discovered; its acceptance and further development 

 will help to establish a broad and unified system of heredity. 



BIBLIOGRAPHY 



Balls, W. L. 1907 Mendelian studies of Egyptian cotton. Journ. Agri. Sci., 



vol. 2. 

 Bateson, W. and Punnett, R. C. 1908 Experimental studies in the physiology 



of heredity. Rep. Evol. Com., No. 4. 

 Baur, E. 1911 Einfuhrung in die experimentelle Vererbungslehre. Berlin. 

 Castle, W. E. 1909 Studies of inheritance in rabbits. Pub. Carnegie Inst, of 



Wash., No. 114. 

 Darwin, C. 1876 The effects of cross and self fertilization in the vegetable 



kingdom. London. 

 Drinkard, a. W. 1908 Inheritance in tomato hybrids. Virg. Agric. Exp. Sta. 



Bull. 177, p. 18. 

 Drinkwater, H. 1908 An account of a brachydactylous family. Proc. Roy. 



Soc, Edinb. 28. 

 East, E. M. 1910 A Mendelian interpretation of variation that is apparently 



continuous. Amer. Nat., vol. 44. 



THE JOURXAL OF EXPERIMENTAL ZOOLOGY, VOL. 16, NO. 2 



