104 Inheritance in the Cowpea 



(3) Pale hy White. 



The White used in this experiment was the same as that used in 

 the series of crosses just described. Owing to a great increase in the 

 number of certain insect pests at the time when the cultures of this 

 cross were being grown, it has only been possible to record the F^ results. 

 In two crosses the F^ was of the Dark type. 



Interpretation of the Experimental Results. 



It has been established most clearly that the two colour types Dark 

 and Pale form an allelomorphic pair. From a less complete series of 

 results it has been concluded that Dark and White also form an allelo- 

 morphic pair. The Fy of Pale by the same White proved to be Dark. 

 These results can be explained by the assumption that flower colour in 

 the cowpea is due to the interaction of two factors : 



L. A factor for Pale. 



D. A factor which increases the amount of anthocyanin colour in 

 the flower but has no visible effect except in presence of L. 



According to this hypothesis the number of possible homozygous 

 types resulting from a combination of these two factors is four, viz. : 



LLDD Dark 

 LLdd Pale 

 HDD White 

 lldd White. 



Dark (LLDD) and Pale (LLdd) differ in one factor D. Hence they 

 are allelomorphic to each other. Dark (LLDD) and White (HDD) are 

 similarly related. Pale (LLdd) by WhitQ (HDD) will give an F^ of 

 composition LIDd which is Dark and will give in F^ a ratio of 

 9i) : 3P : 4Tr. One of the Whites will be the double recessive Hdd. 



II. The Pattern of the Seed Coat. 

 Dr W. J. Spillman (1911) has described several types of pattern 

 characteristic of the seed coat of various races of cowpea, and in his 

 paper gives a diagram of those that he worked with. A representation 

 of his diagram is given in Fig. 1. 



w^m 



f 



Fig. 1. Forms of the " eye" or pigment area, in the seeds of 

 the cowpea. (After Spillman.) 



