V] Colours of Stocks 95 



coupling or to some other cause can only be decided by the 

 circumstances of the special case (see, for example, the case 

 of Stocks, in which plants with hoary leaves are wanting in 

 the classes without sap-colour In the flower (Chap, viii), 

 and the distribution of the hooded standard among Sweet 

 Peas (Chap. ix)). 



Colottrs of Stocks {MattJiioIa), 



The experiments of Miss E. R. Saunders have revealed 

 a closely similar inter-relationship between the various 

 colour-types In Stocks. There also coloured F^^ is produced 

 by crossing two types both destitute of sap-colour. The 

 two types giving this result are white and cream. The 

 pale yellow of the cream Is due not to sap-colour but to 

 chromoplasts, and thus the two types are as regards sap- 

 colour both albinos. In this case also F^ has the common 

 purple flower which we may regard as reversionary*, and in 

 F^ there appear both purples and reds. These results can 

 be represented exactly like those in the Sweet Pea case. 

 The sap-colour is due to the meeting of complementary 

 factors, C and R, derived from the two parents respectively. 

 In the absence of the "blue" factor B^ the colour produced 

 by CR is red, but when B is present the colour is purple. 

 As a matter of fact it can easily be proved that B is intro- 

 duced by the original white parent ; for when a red is 

 crossed with the white, F^ is purple, but when a red is 

 crossed with a cream, F^ is red, showing that the cream is 

 devoid of B, but that the white possesses it. 



The numbers in F^^ are also on the plan described for 

 the Sweet Pea. The total of sap-coloured plants to the 

 total of non-sap-coloured (whites -f creams) averages 9 : 7, 

 and when the proportion of purples to reds is also repre- 

 sented the ratio is 



27 purples : 9 reds : 28 whites and creams. 



Just as In the Sweet Pea again there is a series of 

 subordinate types among the purples in /%, and a corre- 

 sponding series of types among the reds. For example, 

 there is a dilute form of purple which the horticulturists 



* As will be described later, in this case when both parents have 

 glabrous leaves, F^ reverts to the hoary leaves of the original type. 



