H. M. Leake 217 



that the red parent must possess the yellow factor in addition to the 

 red. That this is so will be seen from an examination both of the base 

 of the petal, which usually exhibits a slight yellow colouration on the 

 external surface, and of diseased flowers, in which the petal almost 

 approximates to the red on yellow condition of the impure cross. 



(ii) Type 3 x type 9. As far as the present discussion is concerned 

 this cross differs from the last only in the fact that one of the parents, 

 type 9, has a white, instead of a yellow, petal. The cross is of consider- 

 able interest because on it have been based the greatest hopes of 

 obtaining an improved cotton suitable to the needs of the United 

 Provinces and the results have consequently been investigated in some 

 detail. The present interest, however, does not arise from this aspect 

 but concerns the flower colour. In the F^ generation the corolla is 

 indistinguishable from that of the ^i of the cross previously described 

 and is of the class which has been above denoted as red on yellow, the 

 red petal having round the eye a border of greater or less extent of 

 yellow. (PI. XXXV.) 



From the self-fertilisation of the jP, generation plants are obtained 

 which can by corolla character be divided into four groups : 



(1) Corolla red or red on yellow. 



(2) „ red on white. 



(3) „ yellow. 



(4) „ white. 



In addition to the two original, two additional types of corolla have 

 made their appearance. If now, as in the previous cross, the colour of 

 the foliage is taken into consideration six groups become recognisable. 

 These are : 



This behaviour is readily explained on the assumption that two 

 pairs of allelomorphic characters are here being dealt with : 



(a) Presence of the red factor which has been shown to be dominant 

 to absence of the same. 



(b) Presence of the yellow factor which has been shown (p. 213) 

 to be dominant to absence of the same. 



