338 EXPERIMENTAL STUDY OF INHERITANCE 



should be noted that these peas have the particular advantage, 

 for experimental purposes, that they are habitually self-fertilised 

 — in North Europe, at least. 



In studying the different forms of peas, Mendel found that 

 there were seven differentiating characters which could be 

 relied on : 



i. The form of the ripe seeds, whether roundish, with shallow 

 wrinkles or none, or angular and deeply wrinkled ; 



2. The colour of the reserve material in the cotyledons — pale 



yellow, bright yellow, orange, or green ; 



3. The colour of the seed-coats, whether white, as in most peas 



with white flowers, or grey, grey-brown, leather brown, 

 with or without violet spots, and so on ; 



4. The form of the ripe pods, whether simply inflated, or 



constricted, or wrinkled ; 



5. The colour of the unripe pods, whether light or dark green, 



or vividly yellow, this colour being correlated with that 

 of stalk, leaf-veins, and blossoms ; 



6. The position of the flowers, whether axial or terminal ; and 



7. The length of the stem, whether tall or dwarfish. 



Mendel's Results : The Law of Dominance. — Having defined 

 the differentiating characteristics of the varieties, Mendel pro- 

 ceeded to make crosses between these, investigating one character 

 at a time. Thus, pollen from a pea of the round-seeded variety 

 was transferred to the stigma of a pea of the angular-seeded 

 variety, the stamens of the artificially pollinated flower being, 

 of course, removed before they were ripe. The same was done 

 all along the line. 



What was the result in the hybrid or cross-bred offspring ? 

 It was found that they showed one of each pair of contrasted 

 characters, to the total, or almost total, exclusion of the other. 

 No intermediate forms appeared. 



Mendel called the character that prevailed dominant, and 

 the character that was suppressed, or apparently suppressed, 

 recessive. And the first big result was that crosses between a 

 plant with the dominant character and a plant with the recessive 



