356 E. J. ALLEN. 
shall be capable of germination and growth, the union is necessary of two 
elements which occur in the flower. These elements are the ovule, which 
lies at the base of the flower, and the pollen, which generally takes the 
form of a fine dust or powder, and is formed by the stamens. The pollen 
is the male element, the ovule the female element ; both are single cells, 
and together with the corresponding elements in animals they are called 
by the ceneral name of gametes. The union of the ovule and pollen, which 
results in the formation of the ripe seed, is known as fertilisation. The 
general term applied to the ripe seed, the adult plant or the adult animal, 
which results from the union of the male and female gametes, is zygote— 
that which is yoked together. Two gametes or germ cells unite to form 
a zygote. 
If plants of the variety which produces yellow peas are fertilised with 
the pollen from their own flowers or from flowers of the same variety, the 
seeds produced will all be yellow in colour, exactly resembling the parents. 
The variety breeds true to colour, and for however many generations the 
breeding is continued the colour remains the same, provided both parents 
in every case belong to the same variety. 
Similarly the green-coloured variety, when the flowers are fertilised 
with their own pollen or with that from similar plants, produces pods 
which contain only green-coloured peas. 
What Mendel did was to cross one of these varieties with the other. 
The ovules of a plant normally producing yellow-coloured peas were 
fertilised with pollen from a plant which produced green-coloured peas, 
or vice versd. In this way a hybrid between the two varieties was 
obtaimed. 
The hybrid peas resulting from this cross are all yellow in colour, and 
the result is the same whichever way the cross is made. The yellow 
colour is therefore said to be domimant to green, and green is said to be 
TECESSIVE. 
This is illustrated in Diagram 1, in which the black discs represent 
yellow peas, the rings represent green peas. 
The hybrid yellow seeds were then sown, and the resulting plants 
produced flowers. These flowers were allowed to fertilise themselves— 
that is to say, the ovules were fertilised with pollen from the same flower, 
so that hybrid was mated with hybrid. The pods produced by these 
plants were found to contain both yellow and green peas. The recessive 
form —the green—therefore, which was lost in the first hybrid generation, 
appears again in the second generation. 
As the result of a large number of experiments Mendel found that the 
proportion of yellow to green seeds amongst the offspring of the hybrids 
was 3:1, there were three times as many yellow as green. 
