ALLELOMORPH1C RELATIONSHIPS IN MENDEL1SM 159 



multiple allelomorphs is that concerned with color pattern in Parattetix. 

 Nabours has investigated the inheritance of pattern in fourteen races of 

 this insect, the grouse locust. Some of these are shown in Fig. 73 and 

 also the hybrids between them. It was pointed out in a previous sec- 

 tion in this chapter that these races when hybridized give intermediate 

 forms in F\, intermediate in the sense that they display the type 

 patterns of both hybrids superimposed one upon the other. In F t 

 they segregate into three types, the two parent types, and the hybrid 

 form in the ratio 1:2:1. 



Nabours has prepared a chart from the data of an extensive breeding 

 experiment with some of these forms. It illustrates so admirably the 

 type of behavior displayed by multiple allelomorphs that it is given in 

 full in Fig. 74. In these experiments separation of B from A B and C 

 from AC has not been attempted because the type A exerts very little 

 influence on the color pattern of the hybrid. In this chart expected 

 results are indicated wherever the ratio of types actually observed is of 

 significance. The observed results show excellent agreement with 

 expectations. 



The multiple allelomorphs in Parattetix appear to affect the entire 

 color pattern of the body and to cause different colors to develop in 

 different parts of the body. This, however, is merely another instance 

 of the manifold effects of single factors, and furnishes no sound argu- 

 ment against the conception of multiple allelomorphs. Furthermore, 

 Nabours has discovered at least one modifying factor which can exist 

 only with, and in addition to, any of the fourteen multiple allelomorphs 

 or their hybrids. 



Multiple Allelomorphs in Maize. In maize there is apparently a 

 remarkable series of multiple allelomorphs concerned in the development 

 of red color in the husks, silk, pericarp, and cob. Practically all com- 

 binations of these are known in various different varieties of maize, so 

 that it is possible to have varieties with red grain, silk, cob, and husk; 

 red grain, white silk, white cob, and white husk; or any other com- 

 bination whatsoever. When, however, such types are crossed the FI 

 displays a superimposed set of characters, red being dominant; and in 

 F 2 but three forms appear in the ratio 1:2:1 as with Nabours' locusts, 

 namely the two parental types and, if it is different from either of them, 

 the hybrid form. This indicates that the FI hybrids form gametes 

 bearing factors determining only the conditions represented in the 

 parents. This fact Emerson subjected to direct test by crossing FI 

 hybrids back to varieties lacking the red color in all these parts. In 

 one case an FI plant produced ears which had red cobs and variegated 

 red grains. When such a plant was crossed back to a race having white 

 cobs and grains, the next generation consisted only of plants which bore 



