cH. VIII] Colour and Hoariness in Stocks 133 



F„ from the cross, for instance, of purple x white con- 

 tains sap-coloured and non-sap-coloured plants, and of these 

 some are hoary and some glabrous. But none of the plants 

 which come without coloured sap have any hairs on their 

 leaves. A consideration of the case shows that the factor 

 for hoariness is really introduced by the z£/////^-flowered 

 glabrous plant, and that the glabrousness is due to the 

 inability of the hoariness-factor to make the hairs grow in 

 the absence of the factors for sap-colour. The facts may be 

 represented thus, C and R representing, as before, the factors 

 for sap-colour, and H the factor for hoariness. 



Purple glabrous x White glabrous 

 CRh I cRH 



Fx Purple hoary 



CcRRHh 



I ' 1 



^...9 Purple hoary 3 Purple glabrous 4 White glabrous 



all containing all containing all containing 



C, R, H C,R,h c, R, and B, or h 



If cream glabrous be substituted for white glabrous the 

 result is the same so far as sap-colour and hoariness are 

 concerned, and in /% only those plants can be hoary which 

 also have coloured sap. 



Finally when cream and white glabrous types are crossed 

 together, F^ is purple and hoary, thus showing reversion in 

 colour, owing to the meeting of the two complementary 

 factors C and R, one coming in from the cream and one 

 from the white ; and also reversion to hoariness because the 

 hoariness-factor was really present all the while in both the 

 cream and the white types, but was unable to show itself 

 because one of the sap-colour elements was absent in each 

 type. The heterozygosis of the two types brings together 

 all the three elements C, R, and H, so the Fx plants are 

 both coloured and hoary. 



The reason why hoary-leaved plants are never produced 

 by crossing two types possessing coloured sap is at once 

 apparent. For if the factor for hoariness were present in 

 these types, they would be hoary. 



As may well be supposed the disentangling of these 

 results was a long and tedious process. The occurrences 

 seemed at first contradictory, but after it had been ascer- 



