R. N. Salaman 23 



if both the kidney and the pebble-shaped parent are heterozygous 

 as regards shape, i.e. " length," and amougst the dominants some are 

 excellent kidneys, others pebbles. No. 3 is interesting because it 

 shows on one and the same root a cylindrical fiotato and a pebble, a 

 form which has just been shown to be heterozygous. 



The arguments and the evidence in support of them, as to the 

 heredity of the tuber shapes have, so far, all turned on the fact that 

 there exists a variety of " round " potato which is recessive and breeds 

 true ; at the same time all examples that have been so far brought 

 forward contain directly " Flomball " blood. It might therefore be 

 supposed that the whole structure of my contentions rest on this 

 keystone — this " Flourball " derivative — and that if this latter be 

 removed the argument and deductions would fall to the ground. 

 It becomes necessary, therefore, at this stage to describe an experi- 

 ment entirely free from such an objection, at least as far as I am 

 aware. A cross was made in 1906 between "Red Fir Apple" and 

 " Reading Russet." " Reading Russet " is a pebble-shaped potato 

 and "Red Fir Apple" a long cylindrical. F^ was not examined 

 critically for shape; the note as to the 117 young seedlings raised 

 in 1907 is that about one-quarter bore "round" tubers, of these only 

 nine survived, and only five of them were reared in 1909. Four indi- 

 viduals are shown in Plate XXI, and the fifth one, which was omitted, 

 was a long-shaped tuber. On the whole the evidence is rather in 

 favour of F^ being a mixture of "longs" and "rounds" in the propor- 

 tion of 3 : 1, but of the F^ "rounds" we have no examples. The F^ 

 generation, however, is represented by 120 individuals contained in 

 the two families Z''^' and Z>'^', both derived from the selfing of a 

 kidney-shaped F'- plant. 



The first family, Z''^', consists of 60 individuals; of these 52 are 

 represented in Plate XXII, and of the eight missing, five were long and 

 three "round." When the plate is examined, and still more the actual 

 individuals, the "rounds," such as we have already become accustomed 

 to, are to be found at once, and the following typical examples are 

 seen, Nos. 1, 2, 22, 35, 37, 46, 47, 49, 61, 63 and 64, which in addi- 

 tion to the three not figured, makes the total of 14 out of 60 or 

 nearly 1 : 3. 



The second family, X"", Plate XXIII, afifords some very striking 

 examples of typical "rounds" such as Nos. 6, 47, 52. The family 

 contains 59 tuber-bearing individuals, and of these Nos. 6, 10, 17, 

 19, 22, 24, 29, 30, 33, 40, 47, 52, 54, 61 are typical "rounds," i.e. 

 14 out of 59 or 1 : 3. 



