60 Nebraska Agricultural Exp. Station, Research Bui. 7. 
influencing the extent of pigmentation in the hooded pattern 
but unable to influence the Irish pattern is not so clear. The 
behavior of crosses between a hooded strain with extended pig- 
mentation and one with restricted pigmentation affords support 
to the idea of such additional factors as do also the results of 
crosses between Irish rats and rats with extended hoods whereby 
the hoods of F2 segregates are restricted rather than further ex- 
tended. In short, it seems possible that restricted hood may differ 
from extended hood by one to several genetic factors, just as tall 
bush beans seem to differ from short bush beans, and that Irish 
pattern may sometimes possess and sometimes lack factors for 
extension of the hooded pattern, just as tall pole beans seem to 
possess and short pole beans to lack some factor or factors for 
internode length or internode number — factors which, it appears, 
can be inherited independently of habit of growth and thereby 
be transferred from pole to bush or from bush to pole beans. 
I will admit that at flrst it seems unlikely that a genetic 
factor could be present in the Irish pattern of rats together with 
the factor that differentiates the Irish from the hooded pattern, 
without interfering with the simple 3-1 segregation resulting from 
a cross between Irish and hooded rats. The existence of factors 
for internode length independent of factors for habit of growth 
in beans presents no such difficulty. Apparently the only rela- 
tion that habit of growth bears to internode length exists merely 
by virtue of the circumstance that determinate habit arrests 
growth when the period of acceleration in growth-rate has barely 
begun, so that internode length of bush beans is ordinarily much 
less than that of pole beans. But to conceive the possible nature 
of factors for number of internodes independent of a factor for 
habit of growth in beans presents as great a difficulty as to 
conceive the possible nature of pigment-extension factors in- 
dependent of pattern factors in rats. 
The principal effect upon plant height of indeterminate growth 
is to extend the number of internodes almost indefinitely while 
that of determinate growth is to limit the development of inter- 
nodes to a small and rather definite number. If there are, in 
addition to a single factor for habit of growth, other special factors 
for internode number, how can there result a simple segregation 
giving three plants with many internodes (indeterminate) to one 
plant with few internodes (determinate)? 
Let us see whether the multiple-factor hypothesis — ^assumed 
thruout this paper to interpret the results as regards number of 
internodes in crosses between distinct bush beans and also in 
crosses between distinct pole beans — can be combined with the 
single-factor hypothesis — also used consistently to interpret the 
