Heredity 171 



is the same as (2) except formed by pollen-grain R and 

 egg-cell r, and square (4) is a pure recessive rr in which 

 pollen-grain r united with egg-cell r. 



This may be illustrated diagrammatically in another 

 manner, as in the colored plate (Fig. 44) . 



Explanation of diagram. It is assumed that a variety 

 having red flowers (R) is crossed with another variety 

 having yellow flowers (r). The arrow indicates the 

 direction of the cross and also the transfer of pollen from 

 the anthers of the yellow variety to the stigma of the red. 

 The plants produced from these fertilized ovules will 

 have red flowers because redness is dominant. This F\ 

 hybrid, however, contains both red and yellow qualities 

 and at the time of the formation of its gametes will give 

 rise to red and yellow pollen-grains and egg-cells. During 

 the process of self-fertilization the law of chance will 

 govern the union of the red and yellow egg-cells. These 

 FI ovules will give rise to the plants indicated by F z . 

 The subsequent operations are assumed to follow regular 

 mendelian ratios. 



Mendel's results with the offspring of hybrids in which 

 several differentiating characters are associated. Two ex- 

 periments were made with a considerable number of plants. 

 In the first experiment the parental plants differed in the 

 form of the seed and in the color of the albumen. Experi- 

 ments with seed characters give the results in the simplest 

 and most certain way. 



Experiment 1 . Seed parent = round seeds (R) and 

 yellow cotyledons (Y). Both dominant and hence their 

 symbols are expressed as capital letters. Pollen parent 

 = angular seeds (r) and green cotyledons (y). Round 



