HORTICULTURE AND PLANT IMPROVEMENT 



9 



13. Mendel's law. Mendel worked with the ordinary 

 garden pea. He noted that there are easily recognized 

 differences in different varieties. The peas of some varieties 

 are wrinkled, while others are smooth. Some flowers are 

 purple, while others are red or white. The vine is dwarf in 

 some varieties and tall in others. 



He chose one set of contrasting characters and experi- 

 mented with that. For example, he crossed a purple with a 

 white-flowered variety. When the seed produced by this 

 cross was planted, a vine with purple flowers resulted. But 

 the plants of the generation following this hybridization did 

 not all produce purple flowers. Indeed, one fourth of the 

 plants of this second generation gave white flowers. The 

 remaining three-fourths produced purple flowers. The white 

 remained white through succeeding generations. One-third 

 of the purple remained purple through succeeding genera- 

 tions. Two-thirds of the purple were indeterminate, breaking 

 up in succeeding generations in the proportion of one-fourth 

 pure white, one-fourth pure purple and one-half indeterminate. 

 The following diagram (Fig. 1) shows how the purple color is 

 controlling or dominant and the white not controlling or 

 recessive, the numbers indicating proportions : 



PURPLE PEAS CROSSED 

 WITH WHITE PEAS 



S/PST. 2ND. 3/?D. 4TM 5TH. 



GENERATION GENERATION GENERATION GENERATION GENERATION GENERATION 



7 purpfe-*- purp/p-*- fit/rp/e-* fourp/p-*- 

 '! purpfe-*- fiurfifc *- purpfe^*- 



"1 purfife *- pusyj/e^*- purpte 

 'ffiwpte * jbi/rpfe 



2 fit/tir/d 



2 hybrid 



J white - white 



1 white * white -*- white 



J white ^ white - white * white 



2 white ^ white * white '+- white -+- white 



FIQ. 1. Showing how the purple color ia dominant and the white recessive. 



