Plants in Relation to Man 509 



mathematical ratio is approximately three to one (3 : 1). The 

 66 seeds of the dwarf variety produced plants true to parent 

 type. The 190 seeds from the tall variety produced both 

 varieties of plants in the ratio of three tall to one short plant. 

 The seeds of these short plants produced true to type and so 

 on through all succeeding generations. The seeds of the tall 

 plants produced again about three tall to one short plant. This 

 ratio is always approximately true. The recessives, as every 

 trial shows, come true to type ; the dominants always produce 

 three dominant to one recessive unit character. 



246. Tests of the law. Similar results have been obtained 

 with other kinds of plants and with several kinds of animals. 

 It holds true of wheat and corn. It has also been demonstrated 

 in the cross-mating of white mice with gray mice, of different 

 varieties of rabbits, poultry, cattle, and horses. What may be 

 accomplished in further selection and hybridizing of plants and 

 animals remains for experiment to reveal. 



Application to man. The principle in a general way should 

 hold true of mankind. As a result of Mendel's discoveries 

 much has been achieved in the study of human inheritance ; 

 but this study has really brought to light the difficulties and 

 complexities which must be understood and controlled before 

 great progress can be expected in the application of the prin- 

 ciple to specific cases. In one case, however, we know how it 

 works, namely, in regard to the color of the human eye. 



The colors of eyes may for the present purpose be roughly 

 classified in two large groups, the one containing all dark or 

 brown eyes, and the other all light or blue eyes. Variations 

 between the clear, blue eye color and the deep, dark brown eye 

 color are neglected, as they are generally due to less or more 

 brown pigment in front of the iris of the eye. Dark or brown 

 eye color is known to be a dominant unit character, and light 

 or blue eye color is a recessive. An individual plant or animal 

 may have a character, as tallness, shortness, which is said to 

 be pure-bred or briefly pure, when this character is derived from 



