no BREEDING 



characters we have already considered, such as yellow 

 and green, round and wrinkled ; and before I attempt 

 to show how it can be applied to them I will describe 

 a cross involving two pairs of characters to which 

 its application is obvious. 



This cross is between two kinds of peas (Pisum) 

 which difier in the colour and arrangement of the pig- 

 ment in their seed-coats. In one of them there is a 

 rich brown mottling of anastomosing brown lines on a 

 paler background ; this is characteristic of the 

 so-called " maple," or " partridge," peas which can 

 be had of any corn chandler. The brown mottling 

 is only visible on close inspection ; in the mass the 

 peas appear brown. A specimen of a pea with a 

 " maple " seed-coat is shown, magnified, in Fig. 26. 

 The seed-coat of the other variety, with which the 

 " maple " is crossed, is marked with a great number 

 of minute purple spots on a background, which is 

 pale greenish grey in the newly ripe pea, but becomes 

 dark brown with age. Certain garden peas, such 

 as the French sugar pea, exhibits this type of 

 coloration. A pea with this greyish seed-coat always 

 has purple flowers, whether there are purple spots 

 on the seed-coat or not. Further, the grey may 

 exist in the seed-coat without purple spots, but the 

 purple spots are not known to occur on seed-coats 

 which are not grey. This fact does not concern us 

 now, but is of great importance in the theory of 

 reversion, which will be set forth later. For the sake 

 of brevity, the type of seed-coat which has purple 

 spots on a grey background will be referred to as 



