258 



Biology in America 



modified by other traits) in the make-up of the organism. 

 The basis of this persistence we have already seen to be the 

 chromosome. In those cases in which one character domi- 

 nates another (tallness vs. dwarf ness in peas, color vs. al- 

 binism in animals, etc.), we have the phenomenon known 

 as latency, in which the determiner of a character may be 

 passed along for several generations, without the character 

 itself coming to expression. In such cases the character is 

 definite and the individual is distinct in respect to its pos- 

 session. There is no uncertainty for example, as to whether 



INHERITANCE OF COLOR IN THE FOUR O 'CLOCK 



F,, F 2 , first and second generations. From Morgan, Sturtevant, Mul- 

 ler and Bridges, ' ' Mechanism of Mendelian Inheritance. ' ' 



By permission of J. B. Lippincott Company. 



a guinea pig is spotted or uniform in color, or a man's hair 

 is curly or straight. There are cases however in which the 

 organism is neither "fish, flesh, nor good red herring," or 

 speaking scientifically dominance is imperfect or incomplete. 

 The four o'clock (Mirabilis jalapa) has a white- and a red- 

 flowered race, which when crossed produce plants with pink 

 flowers. When these pink-flowered plants however are bred 

 inter s& they produce 1 red to 2 pink to 1 white offspring, 

 the first and last classes of which breed true, while the mid- 

 dle class when inbred continues to "throw" red, white and 

 pink plants in the above ratio. A crude chemical analogy 

 to these phenomena may be made in the following way : At 



