EXPERIMENTAL STUDY OF HEREDITY 59 



Careful record is kept of all data, and plants produced in 

 this way, with ancestral characters noted and recorded, 

 are called pedigreed. Plantings of such plants are called 

 pedigreed cultures. 



In many species, in "making the cross" {i.e., doing the 

 cross-pollinating) great care must be taken to avoid con- 

 tamination from foreign pollen, of which the air may be 

 full. The fingers and all instruments are usually rinsed 

 in alcohol before each operation, to insure killing any 

 foreign pollen that might be present. Numerous other 

 precautions are also taken. 



When the hybrid plants are mature, careful observations 

 of whatever character is under observation are made and 

 recorded. Whenever possible the observation should be 

 quantitative. 



49. Mendel's Discoveries. — We may illustrate Men- 

 del's results in a simple manner by choosing, as the pair 

 of contrasted characters, smooth and wrinkled seeds of the 

 pea. Removing all the stamens from flowers of a variety 

 having smooth seeds, he polHnated those flowers with 

 pollen from a plant bearing wrinkled seeds. 



It should now be kept clearly in mind Just what the 

 inheritance of the fertilized egg is in such a case. From 

 the pistillate plant the inheritance, contributed by the 

 egg-cell, included the protoplasmic properties (whatever 

 they may be) which, when free to produce their effect, 

 cause smooth seeds; from the staminate parent the in- 

 heritance, contributed by the sperm-cell, included the 

 protoplasmic properties, which, when free to act, cause 

 wrinkled seeds. 



I. Law of Dominance. — What Mendel actually found 

 by his experiments was that, in such a cross, all the seeds 



