Some Apparent Exceptions 87 



parent white peas evidently contained one 

 factor, the other white parent had the other 

 factor in it, and when the two came together 

 the resulting pea plants produced purple blos- 

 soms. Of the offspring of the purple blossom 

 peas 9 contain both factors and are therefore 

 purple, 3 contain one factor, 3 the other, 

 I neither, and all these are white. 



The original wild sweet pea is purple- 

 flowered. The factors for purple have, in the 

 course of cultivation, been separated. The 

 white peas in the experiment each contain one, 

 hence the original purple reappears, a phe- 

 nomenon known as reversion — the reappear- 

 ance of primitive ancestral traits in the 

 offspring of more highly developed animals 

 or plants. Many colts exhibit when very 

 young more or less of the zebra-like striping 

 characteristic of the original horse. Human 

 beings are sometimes born with a harelip or 

 a clubfoot, conditions that are permanent 

 in the lower monkey-like types of mammals; 

 it is easier to bite with the front teeth 

 when the lips can be drawn out of the way. 



