The progress of Genetics since the rediscovery of Mendel's papers. 379 



For example, when a red variety of a plant is crossed with a 

 cream-colonred variety, ivhitcs may appear in F.,. The red variety 

 has red sap, the cream has colourless sap. The cream has yellow 

 plastids. while the red has colourless plastids. 



Fl is red, because red sap is dominant to colourless sap, but 

 colourless plastids are dominant to yellow plastids. The various 

 possible combinations all occur in F«, with the result that 3 plants 

 in 16 have both colourless sap and colourless plastids, and are there- 

 fore white. 



In a tabular form these results may be exhibited thus: 



Parents 

 AUclomorphs 



Red variety X Cream variety. 



(Red sai) (D) 



(Colourless corpuscles (D) 



(Red sap 

 (Colourless corpuscles 



Colourless sap (R) 

 -Yellow corpuscles (R) 



Red sap 

 Colourless corps. 

 Appearance 9 RED 



Red sap 



Yellow corps. 



3 RED-CREAM 



Colourless sap 



Colourless corps. 



3 WHITE 



Colourless sap 



Yellow corps 



1 CREAM. 



Such a case has been seen in both Sweet Peas (Lathyrus odoratus) 

 and in Stocks (Matthiola). (R.E.C. (10 a and b)). 



^^ 



Fig. 8. Various types of Combs in Fowls. 1 The single' comb d^. 2 Pea comb <^. 



3 Pea comb 9. t^ Rose comb in a Bantam o^. 5 Walnut comb in young o^. This 



can be produced by crossing rose with pea. 



