22 Colour and other Characters in the Potato 



will be given proving that there is a tuber shape true to length, but 

 before bringing this evidence forward it will be necessary to discuss a 

 little further the nature of the kidney and the shapes which are 

 heterozygous. 



Plate X shows a family derived from the cross of H^, a kidney 

 whose origin will be described later, and the typical "round" A. The 

 " rounds " can be picked out most readily. 



The typical " rounds " are : 



Nos. 4, 6, 7, 16, 17, 19, 22, 25, 26, 27, 29, 30, 34, 35, 36, 

 38, 39, 40, 42, 45, 49, 



i.e. 21 out of 44, practically half. 



A kidney potato of so typical a shape as H^ is therefore heterozygous 

 in shape, and length, and must clearly be dominant to " roundness." 

 Excellent specimens of kidneys occur in the family, and they must also 

 be heterozygous. 



It is interesting to note that No. 46 is more or less cylindrical, 

 and that it is heterozygous and probably a merely variant form of 

 kidney. 



The hybrid nature, in regard to shape, of the kidney may be regarded 

 as settled, that of the pebble follows as a necessity, but we have in 

 support two sets of crosses. 



A pebble-tubered plant iT" was crossed by the same " round " A 

 as has been used before (see Plate XI). H^'^ is a typical pebble tuber 

 and another of the same root-crop can be seen on Plate IX. The family, 

 consisting of 47 individuals, is seen at once to break up into two types, 

 the " round " and the ovals of different degrees. 



The " rounds " : 



Nos. 1, 2, 3, 4, 10, 11, 13, 13a, 15, 17, 18, 19, 26a, 29, 

 31, 32, 33, 34, 40, 46, 48, 49. 



22 out of 47 are all typical. 



Emerging from this union of pebble and "round" occur really 

 good kidney tubers such as 26, 38 and 41, as good or better than 

 those produced in the family H^ x A, where the parent was a typical 

 kidney. 



The next cross, and perhaps the most convincing, is represented 

 in Plate IX. It was made between a kidney potato, " Record " on the 

 one hand, and the pebble-shaped " Flourball " on the other. The 

 ofTspring number 32, of which Nos. 12, 13, 18, 21, 24, 25, 26, 30 are 

 all typical "rounds"; i.e. 8 out of 32, or 1 : 4, the expected proportion 



