232 Experimental Transformation of Species 



some are wrinkled, and so on. A tall plant may have white 

 flowers or purple flowers. Wrinkled seeds may be yellow 

 or they may be green. Mendel noted in all seven pairs of 

 contrasting characteristics which were apparently constant 

 in the different stocks: 



1. Ripe seeds smooth or wrinkled; 



2. The color of the seed cotyledons yellow or green; 



3. Stem tall {6-j feet) or dwarf (1-2 feet) ; 



4. The pods stiff and inflated or soft and constricted between 

 the seeds; 



5. The unripe pods yellow or green; 



6. Position of the flowers axial or terminal; 



7. Seed coats white or gray to brown. 



Dominant and Recessive 



Mendel's experiments consisted of crossing plants that 

 differed from each other with respect to a given character, 

 disregarding entirely the other characters, although recog- 



Results of Crossing Garden Peas with Contrasting Pairs of 



Characters 



nizing of course that a plant is made up of dozens of traits. 

 In the course of these experiments Mendel discovered that 

 when a cross is made between two individuals of pure strains 

 that differ from each other with respect to a given char- 

 acter, all the offspring have the character of one of the par- 

 ents. When he crossed a tall and a dwarf, the offspring were all 



