74 
Research Bulletin No. 2 
of the cross of Tom Thumb pop and Missouri dent. The differ- 
ence in behavior is undoubtedly due to the fact that in the one 
cross number of nodes was the important consideration while in 
the other it was internode length and to the further fact that F x 
plants in general have an intermediate number of internodes but 
an internode length greater than that of the tall parent. (See 
Tables 31 to 34.) That the tallness of the F x plants of the cross 
under consideration was not due to dominance of long over short 
internodes but rather to the increased vigor accompanying hetero- 
zygosis of many characters is indicated by the fact that the mean 
height of the F 2 fraternities was practically the mid-parental 
height — partial homozygosis having occurred in F 2 — and also by 
the fact that the F 2 frequency distributions were not so pro- 
nouncedly skewed as they would have been if great internode 
length were dominant. The difference between the several F 2 
families is probably due to the presence of heterozygous size 
factors in one or more of the parent plants. No one F 2 fraternity 
covers the entire range between the outer extremes of the two 
parents and no F 2 fraternity fails to bridge the gap between the 
inner extremes of the parents. The larger variation coefficients 
of the F 2 families indicate segregation of size factors in this cross 
where internode length was principally concerned just the same 
as in the other cross where number of nodes was the main 
difference and with this cross, moreover, there can be no question 
of the influence of favorable weather at one time and unfavorable 
weather at another. 
