28 MENDELISM CHAP. 



and that these somethings whatever they were could not 

 coexist in any single gamete. For these somethings 

 we shall in future use the term factor. The factor, 

 then, is what corresponds in the gamete to the unit- 

 character that appears in some shape or other in 

 the development of the zygote. Tallness in the pea 

 is a unit-character, and the gametes in which it is 



FIG. 3. 



Two double and an ordinary single primula flower. This form of double is recessive 

 to the single. 



represented are said to contain the factor for tallness. 

 Beyond their existence in the gamete and their 

 mode of transmission we make no suggestion as to 

 the nature of these factors. 



On Mendel's view there was a factor correspond- 

 ing to the dominant character and another factor 

 corresponding to the recessive character of each 

 alternative pair of unit-characters, and the characters 

 were alternative because no gamete could carry more 



