28 LUTHER BURBANK 



fixed, in the second generation. In such a case 

 the time element may be ignored. 



Take, by way of illustration, Professor 

 Castle's guinea pigs, to which reference has 

 more than once been made. Suppose we have as 

 parent stock a black guinea pig with a smooth 

 coat, and a white guinea pig with a rough coat. 

 Now we have already seen that blackness is 

 dominant to whiteness as regards the coat of the 

 guinea pig, and we must further understand that 

 roughness of coat is known to be dominant to 

 smoothness. 



We must expect, then (according to Professor 

 Castle), that when a cross is made, the guinea 

 pigs of the first filial generation will, unlike 

 either parent, be black in color and rough as to 

 coat. 



But, in the succeeding generation, the black, 

 rough-coated guinea pigs being interbred, there 

 will be a certain number of offspring that com- 

 bine the dominant characters of blackness and 

 roughness of coat, and will breed true to these; 

 a certain number will be black and rough-coated, 

 but will bear the latent characters of smoothness 

 and whiteness of coat which will reappear in 

 their progeny; and, finally, there will appear 

 individuals combining the two recessive traits of 

 whiteness and smoothness of coat. 



