The progress of Genetics since the rediscovery of Mendel's papers. 391 



results shows how peculiar and specific are the properties of the 

 different strains. 



1. Cream glabrous X white g-labrous gave purple hoary 



2. „ „ X purple „ ,, 



3. „ „ X red „ „ red 



4. White „ X purple „ „ purple „ 

 ö \-^ red 



but 6. any red „ \ /any red „ „ fred or\ ^^^^,^^^ 



or purple ,, ) lor purple „ „ (purple J 



The reds and purples have of course coloured cell sap. The 

 cream has no sap-colour, but its plastids are yellow. In the White, 

 both sap and plastids are colourless. The various matings gave F., 

 as follows. 



(1) Cream glabrous X white glabrous. 

 F^ sap-coloured hoary. 



Fg 9 sap-coloured, hoary : 7 non-sap-coloured, glabrous. 

 (2), (3), (4), (5) Non-sap-coloured, glabrous X sap-coloured gla- 

 brous. 



Fl sap-coloured, hoary. 



Fo 9 sap-coloured, hoary : 3 sap-coloured, glabrous, 



4 non sap-coloured, glabrous. 

 (6) Gives only sap- coloured glabrous in F^ and F«. 



A critical examination of these facts shows that there is only 

 one way of bringing them into harmony. The cream and the white 

 glabrous each contain the factor for hoariness, but each has only 

 one of the factors for sap-colour. When they are crossed the two 

 colour-factors ''let each other off", and thus enable the factor for 

 hoariness to produce that effect. Similarly, the sap-coloured forms 

 carry both the colour-factors but are without the hoariness factor. 

 (See E.E.C. III p. 38.)^) 



Finally it can be proved that it is the white which carries the 

 B, or blue, factor; for red X white gives purple F^ while red X cream 

 gives red F^. 



It is evident that the future development of genetics will be 

 largely concerned with such analyses of the interrelation of factors. 

 We are certainly only at the beginning of this part of the inquiry. 



^) By an unfortunate mistake it is stated in Report III that tu-o seimrate 

 factors are concerned in producing hoariness besides those which produce colour. 

 This error arose through a misinterpretation made in earlier stages of the analysis, 

 which was carelessly retained after each of the results on which it was based had 

 been otherwise elucidated. The diagrams and tables there given are correct other- 

 wise, and show clearly that one hoariness-factor is required in addition to the two 

 colour-factors. We are indebted to Mr. Don cas ter for this important correction. 



