64 
Research Bulletin Xo. 2 
INHERITANCE OF HEIGHT OP PLANTS. 
Tables 25, 26, and 27 contain the data on the heights of the 
plants in the three crosses 60-3x54, 60-5x54, and 60-8x54, — Tom 
Thumb pop crossed with Black Mexican sweet. As stated before, 
these crosses differ only in the fact that separate individuals were 
the parents. In a cross-fertilized species like maize, however, 
this might give as varied results as crosses between different 
commercial varieties. The crosses having been made originally 
for the purpose of studying other characters, the height frequen- 
cies of Xo. 60 and of the F 1 generation were not recorded. It is 
only known that the extreme individuals of No. 60 were 22 and 
40 inches and that the extreme individuals of the F t generation 
of cross 60-3x54 were 55 and 88 inches. But one is comparatively 
safe in supposing that both populations exhibited variation 
approaching that of a normal curve. Granting this assumption, 
the modal classes of No. 60 and No. 54 were 31 inches and 73 
inches, respectively. There was a difference, then, of 42 inches 
between the classes of greatest frequency of the two parents, and 
a difference of 18 inches between the plus extreme of the shorter 
parent and the minus extreme of the taller parent. If the F t 
generation was exactly intermediate between the two parents, its 
modal class would be about 52 inches. In reality, however, it 
is about 70 inches. In other words, it has been pushed up about 
six classes above the intermediate position. This phenomenon 
is not to be regarded as an expression of dominance. It is due 
to the increased vigor (largely internodal) that appears when 
manv gametic factors are in the heterozvgous condition (East. 
1909) . 
Since no coefficient of variability of the F a generation can be 
calculated, it is useless to calculate it for the F 2 and F 3 genera- 
tions. There are a number of facts germane to our thesis to be 
discovered by a simple inspection of Table 25. Three F 2 families 
were grown and in every case the extremes of these distributions 
overlap those of the parental distributions. If segregation has 
occurred, F s families from F 2 parents of different height should 
show different average heights and different amounts of varia- 
bility. Such results were obtained. The progeny of several 
short F 2 individuals were, in general, short, and the distributions 
were different in their variability. The mode of the daughters of 
(60-3x54) -5-3 was 37 inches, while the mode of the daughters of 
(60-3x54) -1-7 was 58 inches. The parental types were not re- 
covered in the F 3 generation, but there is good reason — from the 
appearance of the F 3 distributions — to believe this could be done 
by further selection. 
The F 2 distribution in cross 60-5x54 (Table 26) was much 
more variable than the F 1 distribution. Only one family from 
this cross was followed to the F 3 generation, however, so no com 
parison between progenies of large and of small plants can be 
made. 
