38 MENDELISM chap, iv 



Therefore it must have come from the rose, thus 

 confirming our view that the rose is in reaHty a 

 single comb which contains in addition a dominant 

 modifying factor (R) whose presence turns it into 

 a rose. We shall take it, therefore, that there is 

 good experimental evidence for the Presence and 

 Absence theory. Of recent years, however, it has 

 come in for a good deal of criticism in connection 

 with a group of facts which will be dealt with in a 

 later chapter. Whether the conceptions it involves 

 are strictly true or not, it nevertheless provides w 

 with a simple and convenient system of notation for 

 our factors, and we shall express in terms of it the 

 various cases which come up for discussion in 

 succeeding chapters. 



