indistinguishable from the parent with colored flowers. When 
the seed of any one of these reddish-purple flowered plants was 
planted, both purple-red plants and white flowered plants were 
produced in the ratio of three purple-reds to one white. All the 
white flowered and approximately one-third of the purple-red 
flowered plants bred true in the next or third (F 3 ) hybrid genera- 
tion. The other purple-red flowered plants (approximately two- 
thirds of all those in the second generation having purple-red 
flowers) produced seed which again gave the ratio of three with 
colored flowers to one with white flowers. From extensive exper- 
iments tried since, involving large numbers, there is every 
reason to believe that two-thirds of those with colored flowers 
from such a cross after the first generation would always produce 
plants with colored flow r ers and plants with white flowers approx- 
imating a three-to-one ratio. Other pea characters, amounting to 
twelve in all (six pairs), were tested by Mendel in this manner, 
and the results they gave agreed with those of the experiment 
just cited. These included such characters as the color of the 
seedcoat, the color and shape of the cotyledon, the height of the 
plants (tall or dwarf), the color of the unripe pods (green or 
yellow), and the nature of the stem (fasciated or normal). After 
satisfying himself as to the manner in which a single pair of 
characters is inherited, he crossed varieties which bred true to 
two of these differentiating characters. When tall, yellow-seeded 
peas were crossed with dw T arf, green-seeded peas, the offspring 
were all uniformly tall and yellow-seeded. When seed of these 
were sown, four kinds of progeny were produced in approximately 
the following ratio : nine tall yellow-seeded, three tall green- 
seeded, three dwarf yellow-seeded, and one dwarf green-seeded. 
Out of each group a definite proportion bred true to both char- 
acters — in the first, approximately one in every nine; in each of 
the next two groups, one in every three, and in the last group, 
the dwarf green-seeded plants all bred true. 
Space is too short to deal with the character of the remaining 
offspring in the other three groups except to say that a general 
law was followed. Although still more elaborate experiments 
were made, extending over a period of eight years in which vari- 
eties differing in three sets of characters were crossed, nothing 
of an exceptional nature was discovered. So from these and 
other results, Mendel formulated the first clear law of heredity 
extant— the so-called law of segregation. He found that the dif- 
ferent characters in his peas appeared to be inherited as units, 
and that such a character as tallness could be transferred from a 
green-seeded variety to one with yellow seeds independently of 
the other characters such as green seeds with which it had 
hitherto been associated. The next step naturally then, was to 
make a general application of the law— in other words, to consider 
all animals and plants as being made up of many independent 
