OKLAHOMA ACADEMY OF SCIENCE 25 



The meaning of this principle of dominance and segregation 

 may be best illustrated from Mendel's own work. He relates that 

 in experiments in crossing individuals differing in regard to a 

 single pair of characteristics it was found in many cases that "One 

 of the two parental characters is so preponderant that it is difficult, 

 or quite impossible, to detect the other in the hybrid." The follow- 

 ing quotations are from Mendel's paper entitled "Experiments on 

 Plant Hybridization." 



"This is precisely the case with the Pea Iiyhrids. In the case of 

 each of the seven crosses the hybrid-character resembles that of one 

 of the parental forms so closely that the other either escapes obser- 

 vation completely or cannot be detected with certainty. This cir- 

 cumstance is of great importance in the determination and classi- 

 fication of the forms under which the offspring of the hybrids 

 appear. Henceforth in this paper those characters which are trans- 

 mitted entire, or almost unchanged in the hybridisation, and there- 

 fore in themselves constitute the characters of the hybrid, are 

 termed the dominant, and those which become latent in the process 

 recessive. The expression "recessive" has been chosen because tlie 

 characters thereby designated withdrew or entirely disappear in 

 the hybrids, but nevertheless reappear unchanged in their progeny, 

 as will be demonstrated later on." 



"Of the differentiating characters which were used in the 

 experiments the following are dominant : 



1. The round or roundish form of the seed with or without 

 shallow depressions. 



2. The yellow colouring of the seed albumen (cotyledons). 



3. The grey, grey-brown, or leather-brown colour of the seed- 

 coat, in association with violet-red blossoms and reddish spots in 

 the leaf exils. 



4. The simply inflated form of the pod. 



5. The green colouring of the unripe pod in association with 

 the same colour in the stems, the leaf-veins and the calyx. 



6. The distribution of the flowers along the stem. 



7. The greater length of stem. 



With regard to this last character it must be stated that the 

 longer of the two parental stems is usually exceeded by the hybrid, 

 a fact which is possible only attributable to the greater luxuriance 

 which appears in all parts of plants when stems of very different 

 length are crossed. Thus, for instance, in repeated experiments, 

 stems of 1 ft. and 6 ft. in length yielded without exception "hybrids 

 which varied in length between 6 ft. and 7j/2 ft." 



In discussing "The Generation From the Hybrids," he says. 



