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 
full. 1 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. 
