180 THE THEORIES OF EVOLUTION 



Briimi where they remained buried until the botanists 

 Correns, De Vries and Tschermak unearthed them in 

 1900. 



By cross-breeding in different ways twenty-two 

 varieties or sub-species of pea (Pisum sativum) , Men- 

 del observed certain characters such as the shape and 

 colour of seed and pod, the size of the plant, etc., 

 through successive generations, studying each time one 

 single character to the exclusion of the others. 



In order to study, for instance, the color of the seed, 

 he crossed yellow seed peas with green seed peas ; the 

 offspring showed the character of one of the parents 

 only, as yellow seed peas only resulted from the cross. 

 Mendel designated as dominant the character which 

 appeared in this first generation and as recessive the 

 character which did not seem to be transmitted. 

 Thus he came upon his first law, the law of domi- 

 nance. 



Mendel then made a cross between those hybrids 

 which all resembled one of the parents (having yellow 

 seed) and noticed that in the second generation of 

 hybrids some peas gave yellow seed and some green 

 seed in the proportion of three dominant hybrids to 

 one recessive. The disappearance of the green seed 

 character in the first generation of hybrids was only 

 apparent, since this character reappeared in the sec- 

 ond, to which each of the original varieties seemed to 

 have transmitted separately its heritage. Mendel 



