R. N. Salaman 21 



i)^ 1908, a long pyriform tuber. 



D'^, 1909, cylindrical tubers tending to kidney shape. 



D^, 1908, oval or blunt kidney with a sister tuber nearer circular. 



^M909 



The numbers in this case are all too small to draw precise deduc- 

 tions; all that can be said is that D does not represent a fixed type, 

 that, on selfing, it gives both longs and ovals. 



In 190S this same D was crossed by A, and on Plate VIII the family 

 is shown, or rather two families, because two D plants (Z)' and -D") both 

 grown from tubers of the original D of 1907 were fertilized by pollen 

 of ^. 



A glance at the plate is enough to show that one has here two 

 types of tubers, the " round " that we have already discussed on the one 

 hand, and a series of ovals and kidneys on the other. The "rounds" 

 are: 



Nos. 3, 4, 5, 8, 13, 14, 15, 16, 18, 19. 



3, 6, 7, 8, 10, 12, 14, 18, 19, 20, 21, 22, 28. 



That is, 10 out of 19 in the first family, and 13 out of 30 in the 

 second family. Total, 23 out of 49. 



One has, in other words, "rounds" and not "rounds" in practically 

 equal numbers; and it must be remembered that one counts here only 

 those as "rounds" which come well up to the standard already given 

 for a typical " round " such as either A, G^ or G". 



The result of this cross admits of a direct Mendelian interpretation, 

 for inasmuch as A is pure to " roundness," D must be heterozj'gous in 

 that character — a fact which was already strongly indicated befoi-e. 

 And the " non-rounds " must be all heterozygous in shape. If now one 

 examines more closely the " non-rounds," one sees that they are made 

 up of good kidneys such as Nos. 1 (D' x A), and 1, 4, 11 and 26 of 

 (B^xA); of cylindricals, such as 5 and 23 (D" x J.), while the 

 remainder are ovals and pebbles difficult to place, but which include 

 among themselves abundant examples of the same shape as the 

 parent D. 



The experiment therefore as portrayed in Plate VIII is capable of 

 being interpreted as meaning, not only that an oval " pebble " such as 

 shape D is heterozygous as to " roundness," but that a true kidney and a 

 true cylindrical may also be heterozygous in the same degree. Further, 

 if "roundness" (i.e. shortness of axis) is the one allelomorph here in 

 action, then " non-roundness " or length is the other. Later evidence 



