460 TEXTBOOK OF BOTANY 



inflated; others were constricted between the seeds. The seeds within 

 the pods were either all green or all yellow, depending upon the pig- 

 ments in the cotyledons of the embryo. In some pods the seeds were 

 rough; in others they were smooth. 



Peas are naturally close-pollinated, and unless they have been arti- 

 ficially cross-pollinated they may be considered pure-line plants with 

 respect to all of their characters. After studying his plants carefully for 

 two years, Mendel became assured that each of the fourteen varieties 

 named above bred true to type, but he continued to test them for purity 

 throughout the period of experimentation. 



By means of cross-pollination Mendel began to secure hybrids among 

 these plants. We can imagine him with a pair of forceps removing the 

 young anthers from some of the flowers, placing pollen upon the stigmas 

 by hand, and carefully labeling each one with a description of the ovule 

 and pollen parent. Later he collected the ripened pods and seeds, kept 

 them separate, and planted the seeds the following season. 



During this second season he kept a record of the appearance of all 

 the hybrid plants, i.e., the Fi generation. No matter which way the 

 crosses were made between any two of the pure-line plants described 

 above, the influence of certain hereditary factors was found to dominate 

 the influence of others completelv. In these peas the factors that severall)' 

 conditioned the development of tall plants, red flowers, axillary flowers, 

 green pods, inflated pods, smooth seeds, and yellow seeds completely 

 dominated the effect of the factors that conditioned the contrasting 

 characters of dwarfness, white flowers, terminal flowers, yellow pods, 

 constricted pods, rough seeds, and green seeds. Mendel, however, was 

 not the first person to note the complete dominance of some factors in 

 hybrids, and the lack of complete dominance of others. 



When the Fi plants bloomed during this second season, Mendel al- 

 lowed them to self-pollinate naturally. Again he kept careful records, 

 and planted the seeds the following season. From the embryos of these 

 seeds the mature plants of the F2 generation developed. During this 

 third season he obtained an accurate record of more than 5000 progeny 

 of the Fi generation. He continued the experiments for eight years, test- 

 ing and retesting his data and conclusions. Aided by the young men at 

 the monastery he obtained data about many thousands of progeny. 



Mendel had several reasons for choosing the garden pea for his ex- 

 periments. The plants are easily cultivated, they have a short period of 



