MENDEL'S TWO LAWS 57 



and animals, and also from man. He studied the 

 problem from a statistical standpoint, as Mendel 

 had done, but in the material that Galton used, the 

 effects due to the environment were not separable 

 from those due to inherited factors. Moreover he 

 did not give sufficient weight to the fact that the 

 character of an individual is not a suitable index of 

 its hereditarv constitution. 



The latter difficulty was present in Mendel's 

 material also, and one of his chief merits is that he 

 detected this fact by making tests which revealed 

 the hereditary constitution of each individual. 



Mendel deduced two laws of heredity that may be 

 called the Law of Segregation and the Law of Free 

 Assortment. 



Menders First Law 



Mendel's first law can be more strikingly illus- 

 trated today by examples other than those he gave. 

 The inheritance of the red and white colors of the 

 flowers of the common garden plant Mirabilis ja- 

 lapa or four o'clock furnishes an excellent example. 

 If the pollen from a plant with white flowers is 

 placed on the pistil of a plant with red flowers, the 

 seeds that are produced give rise to a plant with 

 pink flowers {jig. 17). The hybrid may be said to 

 be intermediate in the color of its flowers between 

 the two parents. If the hybrid is self-fertilized it 

 produces white-, pink-, and red-flowered plants in 



