304 GERM-CELL CYCLE IN ANIMALS 
separated into two groups; one, containing on the 
average one-third of these plants, was pure yellow and 
homozygous as regards color; the other two-thirds, 
although yellow, contained green in a latent condi- 
tion and were therefore impure yellows and “‘hetero- 
zygous”’ as regards color. The conclusion reached 
was that the eggs and spermatozoa produced by the 
first (F,) generation (see Fig. 81) were pure yellow or 
pure green and that chance combinations during 
fertilization resulted in the three classes of individ- 
uals in the second (F:) generation; that is, one-fourth 
pure yellow, one-fourth pure green, and one-half with 
dominant yellow and green recessive. Evidently 
the factors for yellow and green repulsed each other 
during the maturation so that they became localized 
in different germ cells. 
Such a characteristic as the color of the seeds of 
these peas is known as a unit character, and the sepa- 
ration of the factors of such a character during 
maturation is referred to as the principle of segrega- 
tion. Mendel further discovered that if the seeds 
were also wrinkled or round, such characters behaved 
independently of the color characters. These and 
other experiments described by Mendel opened 
the way for new lines of investigation which have 
yielded results of vast importance from the stand- 
point of heredity and evolution.! 
Soon after Mendel’s results were “‘rediscovered” 
1 For more detailed accounts of experiments and theories that have 
been published within the past fourteen years the reader is referred 
to the books of Bateson (1909, 1913) and Punnet (1911). 
