212 Gates. 



Avhich Mendelians assume? A fallacy frequently indulged in by Men- 

 delian writers is the notion that because various types occur in the 

 offspring of an individual, therefore these were represented in that 

 individual by separate and independent units or factors derived from 

 its parents. The relation of this fallacy to the facts regarding the 

 origin of mutants and the nature of their variability will be apparent 

 later in this paper. 



So far as I am aware, no thoroughgoing Mendelian has ever assumed 

 that the supposed "factors" are ever capable of being distintegrated 

 or modified under any circumstances. 



Finally, by comparing the origin of a new unit character in Oeno- 

 thera with its subsequent hereditary behaviour, we shall have thrown 

 into clear relief the difference between a germinal change and the 

 behaviour of the new character after it has appeared. 



II. Description. 



0. grandiflora X 0. mut. (i) rubricalyx(^) and its reciprocal. 



In igio I made the cross grandiflora x ruhricalyx, the reciprocal 

 cross, rubricalyx x grandiflora, having been made in the previous 

 year. The Fj from both these crosses was grown in 191 1 at the Missouri 

 Botanical Garden, to whose former Director, Prof. Wm. Trelease I am 

 indebted for facilities. In 1912 the F2 of both crosses was grown at the 

 John Innes Horticultural Institution, Merton, Surrey, to whose Director, 

 Prof. Wm. Bateson, F. R. S., I am much indebted for the care with 

 which the plants were handled at every stage so as to prevent the 

 possibility of any mistake. 



A. Methods. 



As is well known, the Oenotheras, which are normally biennial, 

 can be made to develope in one year by starting them in the green- 

 house. My practice has been to sow the seeds in seed pans in January, 

 have the seedlings transplanted into flats after about ten weeks, and 

 plant them out-of-doors about the middle of May. With this treatment, 

 in the English climate practically all of the plants A'ill pass out of the 



(1) In adding the abbreviation mut. I am following the usage suggested by me 

 in a previous paper (Gates, 1913 a, p. 10). In the body of this paper, however, I 

 shall for convenience drop all designations except the one distinctive name of the 

 form, whether species, variety or mutant. 



(2) In all crosses the seed parent is written first and the pollen parent last. 



