EXCEPTIONS TO THE RULES 



245 



flowered stocks from the red and yellow cross. The colors of 

 flowers are due to two causes (see pages 10 and 341), pigments 

 in solution in the cell sap and coloring matters held in the body 

 of plastids. Now the red-flowered stocks have in the petals 

 red-cell sap and colorless plastids (A, Fig. 136), and the yellow 

 flowers have yellow plastids and colorless sap (B). Colorless 

 plastids and red sap are dominant, and therefore, when the red 

 and yellow sorts are intercrossed, in Fj the offspring all have 



Fig. 136. — Showing how the flower color is produced in the offspring of a hybrid pro- 

 duced by crossing red flowered and yellow flowered ten-week stocks. (After data by 

 Bateson.) 



red flowers (C). When, however, segregation of characters takes 

 place in the formation of the spores of the F^ generation, and 

 recombinations occur in self-fertilization, the following sorts 

 result: red sap plus colorless plastids, giving red flowers (C); 

 red sap plus yellow plastids, giving yellowish-red or orange-colo- 

 red flowers (D) ; yellow plastids plus colorless sap, giving yellow 

 flowers (B); and colorless plastids plus colorless sap, giving 

 white flowers (E). 



In many instances the appearance of what seems to be a new 

 character is but the recurrence of a lost one that belonged, it 

 may be, to a far distant ancestor. This would be a case of 

 atavism. The hairy ten-week stocks from smooth parents would 

 be an example of this. There are purple stocks and red stocks 



