82 
Research Bulletin No. 2 
INHERITANCE OF INTERNODE LENGTH. 
From the data given for height of stalks and number of nodes 
of the crosses of Tom Thumb pop with Missouri dent and of the 
latter with California pop, the average internode length per plant 
was determined. Tables 33 and 34 contain these calculated data. 
While in 1909 the height and number of nodes were determined 
for each individual plant, only the frequencies of the various 
height and node-number classes were recorded. It is impossible, 
therefore, to show even the range of internode length for the lots 
grown that year. From the mean heights and the mean number 
of nodes of these lots, however, an approximation of the mean 
internode length can be obtained. These approximate means are 
indicated by crosses in Table 33. The feature of these entries 
is that the mean internode length of the F x generation is much 
greater than that of even the Missouri dent parent. It is evident 
that the increased vigor of F x plants is manifested almost wholly 
by increased internode length, since, as was shown in Table 31. 
number of nodes is distinctly intermediate. 
In 1910, very moist conditions in early summer, when Tom 
Thumb pop was making its rapid growth, and very dry condi- 
tions when the later Missouri dent and F x plants were growing 
most rapidly, tended to equalize the internode lengths of the 
several families. Notwithstanding this the F t internode length 
was considerably in excess of that of Missouri dent. The mean 
internode length of the F 2 generation was somewhat less than 
that of F x — doubtless because of the decreased vigor accompany- 
ing partial homozygosis of various characters — but was still in 
excess of the internode length of Missouri dent. The range of 
variation in F £ , No. 510, was somewhat remarkable when con- 
sidered in connection with the ranges of the parents. The 
greatest internode length in F 2 was thirty millimeters greater 
and the shortest thirty millimeters less than the respective ex- 
tremes found among the parents. This increased range may 
doubtless be accounted for in part, tho certainly not entirely, 
by the fact that more individuals were included in F 2 than in 
all the other lots together. It seems scarcely possible that the 
very weather conditions that tended to increase the internode 
length of the early Tom Thumb pop and to decrease that of the 
late Missouri dent, and thereby to restrict the combined range 
of variation of the parents, could have had the opposite effect 
on the F 2 range. There was, as a matter of fact, in this par- 
ticular F 2 family, No. 510, a correlation between earliness and 
internode length of about .21. In other words, there was some 
tendency at least for the early plants to have long internodes 
and the late plants short internodes. This correlation is prob 
