556 



THE PURE LINE II V}>OTHESIS. 



of red plants tend to< be more richl}' coloured than the flowers 

 which have just opened. 



The intensity of the red colouration of the flower is thus 

 the result of the reaction of several accents, such as the amount of 

 oxidase present and the amount of the inhibitor or inhibitors, 

 since a minute amount of the latter might not entirely prevent 

 the oxidase from having some eltect. It has not been ascertained 

 whether some of the plants are pale yellow on account of the 

 complete absence of an oxidase, or whether this condition is 

 always due to the presence of inhibitors. The subject requires 

 investigation. 



From these considerations it is not surprising that the rela- 

 tive numbers of red and yellow plants which result from various 

 crossings should appear erratic, and not follow the simple Men- 

 delian ratio of i : 3. The actual numbers obtained may now be 

 given. 



The $ progenitor (A) had medium-red flowers, and the 2 

 progenitor (B) had pale yellow flowers, with the ordinary red 

 " honey-guides." We have already seen that on selfing A seven 

 offspring were obtained, and they were all red ; and on selfing B 

 there were 20 oflr'spring, and of these, three were red and the 

 remaining 17 were not red. 



On crossing B with the pollen of A 21 hybrids were 

 obtained ; of these, 20 possessed red sap, and one only had no 

 tiace of redness on the general surface of the petals. The inten- 

 sity of the red colouration of the hybrids varied greatly, and the 

 percentage-grade of each plant is given in the following table 

 in ascending order of intensity: 



A ( S ) Redness 60 % X B ( 5 ) Redness o %. 



Here, then, we have a family consisting of individtials 

 which exhibit a varying amount of redness in the flowers, and 

 the problem is to determine how far the intensity of colouration 

 can be transmitted to the offspring on self-fertilising these 

 individuals. According to the pure-hne hypothesis, the family 



