ii6 BREEDING 



sideration the results are supposed to be complicated 

 by the fact that one of the characters of one pair is 

 affected by a character belonging to the other pair. 

 It is supposed that the character " purple spot " 

 can only exist in a pea which has a grey seed- 

 coat. In other words, the character " purple spot " 

 cannot be manifested unless the character " grey " 

 is also present. But the character "grey" can be 

 manifested in the absence of the " purple spot." If 

 there was not this connection between the characters 

 of two distinct pairs we should expect the composition 

 of the second hybrid generation to be analogous to 

 that which we have seen to follow from other instances 

 in which two pairs of characters are involved. We 

 should expect it to consist of 9 grey with purple 

 spot (two dominant characters), 3 grey, but with- 

 out purple spot (one dominant and one recessive 

 character), 3 purple-spotted, but without greyness 

 of seed-coat (one dominant and one recessive 

 character), and one white, i.e. without purple spot or 

 greyness (two recessive characters) : an ordinary 

 9:3:3:1 proportion. This is what we should 

 expect if we did not suppose that purple spot and 

 greyness of seed-coat were connected in the manner 

 stated above, viz. the impossibility of the mani- 

 festation of purple spot in the absence of grey ; and the 

 possibility of the manifestation of grey in the absence 

 of purple spot. Now, let us see how this supposition 

 affects the 9:3:3:1 ratio. The second 3 represents 

 three plants the seed-coats of which would exhibit 

 purple spots on a white seed-coat on the supposition 



