20 SIZE INHERITANCE IN RABBITS. 



hybrid ratios obtained in crosses with white were due to the presence 

 and absence of a color factor, as was suggested above? If this is at 

 all correct a similarity is seen between this and the crosses in which 

 factors of different strength affect the same character. The absence 

 or presence of the strong color factor, a factor whose absence can not 

 be questioned, makes the monohybrid ratio apparent, while the weaker 

 factors for special color indicate their segregation by the new combina- 

 tions and the new shades resulting from them. 



SIZE CHARACTERS SHOWING MENDELISM. 



Various cases will now be presented of the inheritance of size char- 

 acters which appear to follow Mendelian expectations more closely 

 than the preceding examples. A most instructive investigation on the 

 inheritance of the height of peas has been presented by Keeble and 

 Pellew (1910). Two semi-dwarf races of peas with very constant 

 heights of 3 to 4 feet gave an F x of 7 to 8 feet. In F 2 plants were found 

 ranging between 1.5 to 8 feet. This is very much like the cases cited 

 above of crosses between strains having a similar character which 

 becomes variable in F 2 ; but here the different factors that produce 

 height have been more definitely analyzed. One parent had thick 

 stems and short internodes; the other had thin stems and long inter- 

 nodes. In F 2 the tall plants had long internodes and thick stems, the 

 short plants had short internodes and thin stems, while half the inter- 

 mediates had long internodes and thin stems and half had short inter- 

 nodes and thick stems. Two characters tend to lengthen the plant; 

 the internode length and the thickness (which was supposed to enable 

 the internode to attain greater length). The ratios in the four classes 

 closely approximated expectation. The classic case of tall-dwarf peas 

 described by Mendel has been paralleled in other plants. Bateson and 

 Punnett (1908) show that tallness and the unbranched habit in sweet 

 peas are simple Mendelian dominants to dwarfness and the branched 

 habit. The branched habit is dominant to the unbranched habit in 

 stocks (Saunders, 1911). Emerson (1904) has shown that the axial 

 position of the pods of beans is dominant to their terminal position. 

 Tall and dwarf Antirrhinums act as a Mendelian pair (Baur, 1911). 

 Tomatoes have dwarf varieties that have been demonstrated by Price 

 and Drinkard (1908) to act as Mendelian recessives when crossed with 

 normal lines. Salaman (1910) believes that length of the potato tuber 

 is dominant to roundness. The long and short styles of Oenothera 

 form a Mendelian pair (de Vries 1901, p. 435). 



In animals the clearest cases of simple Mendelian inheritance in size 

 characters are found in the long and short wings of Drosophila (Morgan, 

 1911) and in brachydactylous digits in man (Farabee, 1905, and Drink- 

 water, 1908). James Wilson (1909) shows that short stocky legs is a 

 dominant character in the Dexter-Kerry breed of cattle. 



