34 Colour and other Characters in the Potato 



The numbers in the latter are not conclusive in themselves, because 

 only selections of these families were actually planted out ; but amongst 

 the young seedlings, before planting out, there were 23 red to 8 white 

 and the appearance of the harvested selections fully bear out the sug- 

 gestion of a 3:1 ratio. 



Purple Coloured Tubers. — The "Congo" potato is a cylindrical 

 potato of almost a black colour, the pigment extending within the 

 tuber somewhat irregularly. The " Congo " flower, which is white with 

 a purple tinge at the base of the petals, is completely sterile in the 

 male organs, and it was therefore only used as a mother plant. 



Two crosses were made — 



1. Congo X Reading Russet. There were eight seedlings and only 

 four survived until the late autumn of 1906, of these 



Two were black like " Congo," 

 Two bright red. 



But on July 25, 1907, there was a fifth plant with white tubers which 

 died out subsequently. 



The numbers are too small to make any deduction as to ratios, but 

 there is one factor of great importance which stands out, viz. — that out 

 of a union of a deep purple and weak red, there have segregated out 

 deep purple (black), bright red and white. 



The next cross was — 



Congo X Flourball Seedling. This cross was effected in 1906. The 

 " Flourball " seedling was a stray plant growing in one of the experi- 

 ment lines containing " Ringleader " and was used as pollen parent. 

 " Ringleader " itself did not flower that year. Except that it was 

 a red tubered variety nothing further can be told about it, as it was 

 unfortunately not preserved. Its pollen was used in the cross with 

 "Queen of the Valley" and, as has been mentioned before, it is probable, 

 for the reasons already given, that it was a red of the formula RrDD or 

 RRDd. 



The F^ generation contained 29 plants and these were 

 13 Black tubers. 

 12 Red tubers. 

 4 White tubers. 



Here again the important features are the complete segregation and the 

 appearance of the white tubers. 



Before discussing the possible constitution of " Congo," it will be 

 best to consider the F^ generation. 



