98 



Heredity and Eugenics 



When crossed at random, there are 7X6 = 42 possible com- 

 binations of which 24 give all white seeds and 18 give some 

 purple seeds. Of these 18 ears there would be on the aver- 

 age 2 pure purples, 8 with purples and whites in a ratio of 

 i : i, and 8 with purples and whites in a ratio of i : 3. Such 

 results have been obtained experimentally and examples 

 are shown in Fig. 42. 



FIG. 42. Reversion due to latency of separation. Purple seeds produced by 

 crossing whites. Ear i, i to 3 ratio; ear 2, i to i ratio. 



A different kind of latency is simply invisibility of a 

 character due to some obscuring factor which may be 

 removed by means of a cross in which the latter is absent. 

 This latency is called that of hypostasis, a hypostatic char- 

 acter being one which is obscured by another called the 

 epistatic character. There are instances where this epi- 

 static character may be removed mechanically and the 

 hypostatic character revealed. Such a one is the red-eared 

 maize, for the color there lies in the hull or pericarp. This 



