50 HEREDITY 



varieties showing very sharply differentiating characters ; 

 the plant may be tall or dwarf, the seeds green or 

 yellow, round or wTinkled, and so forth. 



Mendel crossed pairs of varieties showing these sharp 

 differences in one or more points, and noted the manner 

 in which the following generations inherited the special 

 characters of either j)arent. 



It is impossible here to go fully into the technical 

 method of effecting the cross. In essence, the process 

 is to emasculate one flower, which is to form the female 

 parent, by removing the anthers before they have shed 

 their pollen. Wlien this flower is mature, pollen is 

 obtained from a flower of the plant selected as the male 

 parent, and this is brushed on to the stigma or female 

 receptive surface of the emasculated flower. The seeds 

 formed from this flower ^^'ill produce hybrid plants. 



What Mendel discovered from his experiments may 

 best be explained by describing the results of one of 

 them. He crossed a tall form of pea "uith another of 

 the weU-known dwarf t3rpe. The difference consists 

 in the one having long intemodes or joints between 

 successive leaves, \^'hile the other has short. The tall 

 type measured about six feet in height, the dwarf 

 about eighteen inches. 



On raising the hybrid plants, the somewhat remark- 

 able observation was made that the plants were aU as 

 tall as the tall parent. We usually expect a hybrid 

 or cross-bred to partake somewhat of the character of 

 both parents, but this did not occur. Mendel expressed 

 tliis fact by sajdng that the taU condition was dominant, 

 the dwarf condition recessive. 



Mendel allowed these tail hybrids to produce seed in 

 the ordinary way — i.e. by self-fertihsation. The follow- 

 ing generation, when raised, was found to consist of 

 two classes — tails of equal stature to their tall grand- 

 parent and their own parents, and dwarfs which were 

 just as short as the dwarf grand-parent. There were 

 no intermediate specimens. The dwarf condition which 

 appeared to have been lost in the first hybrid generation 

 thus reappeared in the second. Moreover, the number 



