R. N. Salaman 25 



In 1908 a cross was effected between a pebble-shaped tuber (71/°, 

 Plate XXIV) and a seedling of the family B carried on by tuber from 

 1907'. The issue of this union forms a striking example of the effect 

 of crossing a heterozygous by a dominant long. The whole family of 

 39 individuals is without exception long or oval, and includes the most 

 elegant kidney and one or two cylindricals, see Plate XXIV. 



In three experiments cylindrical potatoes were employed as the 

 female parent. In the first " Red Fir Apple," a cylindrical, was crossed 

 by " Reading Russet." There is good reason to believe that the i^' 

 family really consisted of three " longs " and one " round," though the 

 small number of survivors, viz. 11 in the first season, does not assist 

 one to any definite conclusion. Those of the F^ family which survived 

 1909 are shown on Plate XXI. " Red Fir Apple," though long and 

 cylindrical, is therefore in all probability heterozygous as regards 

 length. It is of interest that, since it has been cultivated in my 

 garden, it has become shorter and broader and less cylindrical ; on 

 the other hand " Congo," which was used in the second and third 

 experiment, maintains its truly cylindrical shape. Plates XII and 

 XXV. 



In the second experiment "Congo" was crossed by a " Flourball " 

 seedling of 1906. The "Congo" tubers are typically cylindrical, 

 the seedling "Flourball" was not especially described^ but the F^ 

 series, see Plate XXIX, consisting of 29 individuals, all of which 

 bore kidney-shaped tubers, is evidence that the " Flourball " seedling's 

 parent must have been "round" and that "Congo" must be a pure 

 dominant ; for if neither of these suppositions are true, then we should 

 have expected pure " rounds," which are conspicuously absent, or if 

 the " Flourball " seedlings were pebble or heterozygous in shape, then 

 half of the K seedling family should be pure " longs," which they are 

 not. F^ families were raised from K*^ and K^, both elongated and 

 more or less kidney-shaped. The following proportion of "rounds" 

 and " longs " occurred : 



Eounds Longs 



Family 7C6 65 210 



FamHy A'3 13 69 



78 279 



' The B line planted in 1908 from the pollen of which this cross was made, was 

 grown from long tubers arising both from the plant which gave the seed ball in 1908 

 and from its sister plants, sown indiscriminately. 



^ The absence of a description of shape implies that it was "round" or "pebble" 

 shaped and not markedly distinct from the parent " Flourball." 



