356 EXPERIMENTAL STUDY OF INHERITANCE 



Mendelian interpretation has an experimental, not a speculative 

 basis ; (3) because if these elaborations are justified we are led 

 to caution in denjdng Mendelian inheritance in cases where its 

 absence is only apparent ; and (4) because the added concep- 

 tion of allelomorphs or contrasted unit characters working 

 in pairs, abetting or counteracting one another, seems to us to 

 bring the Mendelian theory into close approximation to the 

 Weismannian conception of the struggle and interaction and 

 co-operation of determinants. 



Mendel's Results summarised. — i. The first result was the 

 demonstration of the law of dominance, D x R = D(R). 



2. The second result was the demonstration of the law of the 

 splitting or segregation of the offspring of inbred hybrids into 

 forms showing the dominant character and forms showing the 

 recessive character, with on the average definite proportion (3:1) 

 between the two sets : D(R) x D(R)=i DD 4- 2 D(R) + i RR. 



3. The third result was the conception of alternative pairs 

 of " unit characters " (Bateson's allelomorphs), which behave in 

 inheritance as if they were discrete unities. 



4. The fourth result was the theoretical interpretation of the 

 second, as due to segregation of the gametes into two equal groups , 

 one bearing the dominant character and the other bearing 

 the recessive character. 



§ 4. Illustrations of Mendelian Inheritance 



How far has Mendel's Experience been confirmed ? — There 

 has been confirmatory work by Correns (on peas, maize, and 

 garden-stock), by Tschermak (on peas), by De Vries (on maize, 

 etc.), by Bateson and his collaborators (on a large variety of 

 organisms), by Darbishire (on mice), by Hurst (on rabbits), by 

 Toyama (on silk-moths), by Davenport (on poultry), and so on. 

 There are some difficulties and not a few discrepancies, but, as 

 Bateson says, "the truth of the law enunciated by Mendel is 



