EXPERIMENTAL STUDY OF HEREDITY 553 



the hybrid. 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 

 fuU.^ 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 observa- 

 tions of whatever character is under observation are 

 made and recorded. Whenever possible the observation 

 should be quantitative. 



474. 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 pollinated 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 



1 See p. 423, paragraph 376. 



