H. M. Leake 215 



over-estimating the intensity of the colour, while in 2 eases only out 

 of 138 the error was made in the direction of under-estimation giving 

 a combined error of approximately 1 in 25. In Table III (6) a larger 

 error occurs, the intensity of the colour having been over-estimated in 

 4 cases out of 63 and under-estimated in 22 cases out of 212, making 

 a combined error of 1 in 10. As a generalisation it may be said that 

 in the intensity of the colour in the leaf there exists a character by 

 means of which it is possible to separate with a fair degree of certainty 

 the pure dominants of the form DD from the impure dominants of the 

 form DR. 



The presence of the red factor does not, however, merely find its 

 expression in the leaf. As has been stated it is universally present 

 and is readily identified in organs devoid of chlorophyll such as the 

 petals. Under these circumstances it would seem probable that the 

 intensity of the colour would be most readily determined in an organ 

 like the petal where the colour is not masked. A reference to Table IV 

 will show, however, that this is not so. Gradation in the case of the 

 petals does not occur as one of intensity but one of area. The petal is 

 either entirely red or red with areas, greater or less in extent, situated 

 round the eye in which the red colour is absent. Such plants, in the 

 case of a cross between a red, and a yellow, flowered type have 

 been recorded as having the petals red on yelloiu. As Table IV (a) 

 indicates, among 201 plants, 30 were recorded as having the petals 

 red and the remaining 171 plants as having the petals red on yellow. 

 Actual experiment has, however, shown that in reality 63 of the plants 

 used as parents were of the form DD. The petal colour, therefore, 

 failed to distinguish between the pure, and impure, forms in 33 cases 

 out of 201. This error of approximately 1 in 6 compares very un- 

 favourably with the error of 1 in 25, which was obtained when the 

 colour of the leaf was considered. 



Table IV (6) is derived from the cross between a type with red, and 

 one with white petals, and in it only that section of the F2 genera- 

 tion in which the dominant yellow occurs has been considered. In 

 this example an error occurs in 49 out of 196 instances making an 

 error of 1 in 4. In both cases the error is considerably enhanced when 

 the determination is made on the flower instead of the leaf. In spite 

 of the masking effect of the chlorophyll, therefore, the intensity of the 

 sap colour is most readily identified in the young leaf and, determined 

 in this manner, affords the most accurate guide to the purity, or 

 impurity, of the plant with respect to this character. 



