iv PRESENCE AND ABSENCE THEORY 31 



ing to the dominant character or a definite something 

 corresponding to the recessive character, 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 corre- 

 sponds 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 



Fig. 3. 

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



the single. 



which it is 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. 



