24 Colour and other Characters in the Potato 



In the two families containing 119 tuber-bearing individuals, 29 

 are "round," that is 1 in 3, as would be expected in an F^ family 

 from a heterozygous parent in which "roundness" was recessive. 



It remains now to consider the evidence bearing on the existence 

 and nature of the dominant shape in its pure form. So far, it has 

 been shown that length of tuber is dominant and that the degree 

 of dominance is variable, i.e. the hybrid form is not constant, the 

 heterozygous tubers varying from a long kidney to an ovoid. On 

 Plates XXII and XXIII, amongst the long tubers are undoubtedly 

 pure dominants, but which exactly they are, and how to distinguish 

 them from the impure dominants with certainty nothing but breeding 

 experiments could determine. 



It is, however, significant that by selecting those individuals whose 

 tubers were the most uniformly long, it was found that out of the 119 

 members of the L family already described there were 34, or a little 

 more than one-quarter, that could be picked out as being probably 

 pure in respect to length. 



Fortunately better evidence is to hand in respect to individuals 

 homozygous in the character of length. 



A potato, called "Sole's Kidney," yielded abundant seed in 1906, 

 in 1907 several hundred seedlings were planted^ and they all came 

 true to type, viz. a long attenuated kidney, see Plate XXVI. One of 

 these seeded and 50 seedlings were raised in 1909, and every one 

 of these were long kidney form, see Plate XXVI. It would seem, 

 therefore, that this potato G, " Sole's Kidney," is a pure dominant as 

 regards length. 



Another kidney, "Bohemian Pearl," was sown in 1907 and a very 

 large number of seedlings (family B) raised ; these were not examined 

 very critically in respect to size and shape, but were noted as being 

 uniformly long and pyriform : one selfed naturally, and of the five 

 seedlings raised three bore long tubers, and two bore oval tubers, 

 Plate XXV. These ovals are distinctly flattened and are not " rounds." 

 They have been grown in 1909 and have retained their shape. Had 

 there been any appreciable number of oval or "round" tubers in the 

 first batch of 300 seedlings raised in 1907 it would undoubtedly have 

 been noted ; on the contrary, my own and my gardener's impression is 

 that nothing but "longs" occurred. There is in my mind but very 

 little doubt that the stock B is pure to length. Efforts are being made 

 to self the oval tubered plants this season. 



1 I was presented with several hundred of the seed of both these stocks by the Manager 

 of the Cambridge University Farm. 



