INTERPRETATION OF REVERSION 115 



peas characterised by these two types of seed-coat are 

 crossed, the resultant hybrid may either have a seed- 

 coat like the grey parent or it exhibits the full 

 purple spotting. This latter result is shown in Fig. 27, 

 the hybrid grey seed-coat with purple spots being 

 seen below and between the two parent forms. The 

 hybrid here possesses a character, the purple spot- 

 ting, which is absent from both parent forms, but 

 exists in the wild pea found in Palestine and elsewhere, 

 which probably corresponds more closely than any 

 other to the wild ancestral form from which our 

 cultivated peas have descended. The reappearance, 

 therefore, of this purple spotting as the result of a 

 cross between two forms, neither of which possesses 

 it, constitutes a typical instance of reversion or 

 throwing back. 



The second hybrid generation, produced by the 

 self-fertilisation of these reversionary hybrids, consists 

 of peas with purple -spotted grey seed-coats, peas 

 with grey seed-coats, and peas with white seed-coats, 

 in the ratio of 9 purple-spotted grey, 3 grey, 

 and 4 white. This is an entirely new proportion, 

 the meaning of which is not at first sight obvious. 

 The theory which has been put forward to explain it 

 is as follows : It is supposed that two pairs of 

 characters are involved in this cross : they are 

 " grey " and " absence of grey " ; and " purple spot " 

 and " absence of purple spot " — exactly as in the 

 instance described at the end of the last chapter, 

 " maple " and its absence, and " purple spot " and 

 its absence. But in the instance now under con- 



