2 A MANUAL OF MENDELISM 



decided to breed a number of hybrids and follow their 

 descendants through as many generations as might be 

 necessary, and, to make sure that his materials were 

 suited to his purpose, he laid down the following as the 

 conditions which the plants to be made use of should 

 fulfil : 



(a) The parents should differ from each other in 

 clear and well-defined characters. 



(b) They should breed true. 



(c) They and their descendants should be naturally 

 protected or readily protectable from strange pollen 

 during the flowering season. 



(d) Their descendants should not suffer seriously from 

 infertility. 



In Mendel's opinion, the plant which fulfilled these 

 conditions best and was, at the same time, easily 

 cultivated was the ordinary edible pea. The seeds of 

 34 varieties were purchased and two generations grown 

 to discover whether they bred true * before any ex- 

 periments were begun. Of the 34 varieties 22 were 

 retained, and, for the first series of experiments, 14 were 

 chosen which could be arranged as 7 pairs, in all of 

 which one of each pair differed from the other in one 

 well-defined character. The following table gives the 

 characters in which the members of each pair differed : 



In one member In the other 



1. The seed-coat was round. The seed-coat was wrinkled. 



2. The seed had yellow " albumen." The seed had green " albumen." 



3. The seed-coat was coloured. The seed-coat was white. 



4. The pods were plain. The pods were constricted. 



5. The unripe pods were green. The unripe pods were yellow. 



6. The flowers were axial. The flowers were terminal. 



7. The stems were 6 to 7 ft. long. The stems were | to IJ ft. long. 



* This treatment was continued till the end of the experiments. 



