34 
Research Bulletin No. 2 
ing, and perhaps also because of previous selling, produced few- 
ears. The entries in the table under the designation of Tom 
Thumb pop and of Missouri dent, like those of the F t genera- 
tion, were obtained from such ears of these varieties as had been 
preserved as samples. 
Such data as are available indicate a 12-rowed type for Tom 
Thumb pop. The range of variation indicated for Missouri dent 
suggests that the stock of that variety used may have been 
heterozygous for several factors for number of rows, with a 
tendency to produce 16 to 20 rows per ear. The three F 2 families, 
510 grown in Nebraska in 1910 and 1127 and 1128 grown in 
Massachusetts in 1911. were somewhat dilferent in the mean 
number of their rows and in their ranges of variation. Such 
behavior as this was to have been expected if either or both of 
the parents were heterozygous for any of the factors concerned 
in determining number of rows per ear. The range of variation 
in the F 2 fraternities extended somewhat beyond the extreme 
ranges of the parent varieties — if indeed the records available 
can be said to show the ranges of the parents. 
The best evidence of real segregation in F 2 of the factors for 
number of rows is furnished by the F 3 families. As pointed out 
more fully later, in the discussion of inheritance of height of 
stalk, the differences between the several F 3 lots under con 
sideration here cannot be ascribed to the possible heterozygous 
condition of the parent plants used in this cross, because all The 
F 3 families are descendants of one F 2 fraternity. No. 510, which 
in turn, of course, was the progeny of a single I\ plant. What 
other F 2 progenies or other Fj plants may have been like or 
even what other sorts of gametes the parent plants may have 
produced, in addition to the two gametes whose union resulted 
finally in these F 3 families, is absolutely immaterial. Since all 
these F R families were related in this way. their differences are 
ascribable only to segregation of size factors in F 2 . Among the 
F 3 lots, there w^ere included at least one 12-rowed type, 1142, like 
Tom Thumb pop, several lots of a 16-rowed type, and tw^o or 
three of a 20-rowed type, particularly 1140 and 1141. with per- 
haps also 14-rowed and 18-rowed types. 1144, 1134, 1135, etc. 
That a type with more than 20 rows might be isolated by selec- 
tion from a family like 1140 seems probable, but the possibility 
can be tested only by further breeding. 
