96 
Research Bulletin A o. 2 
INHERITANCE OP DURATION OF GROWTH. 
While the time required for a corn plant to reach a definite 
stage in its development, such as blossoming or ripening, is not 
strictly a size character, it has nevertheless a marked influence 
upon the size of plants or plant parts. It has been pointed ou' 
earlier in this paper how earliness and lateness may affect the 
height of plants if the season is more favorable at one time than 
at another. Besides this effect it is reasonable to expect a physi 
ological correlation between size and duration of growth. 
Obviously an extremely early plant cannot in its few weeks of 
growth attain a height equal to that ultimately reached by an- 
other plant whose period of growth extends thruout the entire 
summer. It does not follow from this, however, that there is 
any genetic correlation between duration of growth and ultimate 
size. Later in this paper we shall consider this point further. 
The general average difference between times of flowering in 
various F 3 families of Tom Thumb X Black Mexican was very 
marked. Family (60-3x54) 1-2AS was two weeks earlier than 
(60-8x54)8-808." 
The cross of Tom Thumb pop with Missouri dent furnished 
favorable material for a study of the inheritance of length of 
growing period. Missouri dent is so late that it barely ripens at 
Lincoln. Nebraska, while Tom Thumb pop is one of the earliest 
varieties known. In 1910 both varieties were planted together 
on the same day and ripe ears of Tom Thumb pop were harvested 
the same day that some of the Missouri dent plants were 
pollinated. 
The two dates that perhaps best measure the duration of the 
growing period are the date of planting and the date of ripening 
of the ears. It is difficult, however, to tell exactly when an ear is 
ripe. Hardness of kernels and dryness of the outer husks were 
taken to indicate ripeness, but it can never be said that the 
husks were green yesterday and are dry today. The date of 
blossoming can be fixed much more definitely than the date of 
ripening, but growth has not ceased at this time. The ears, in 
fact, make their principal growth after blossoming. The growth 
in height of stalks, however, is practically complete at blossoming 
time, so that this date and the planting date can be used to de- 
termine roughly the period of height growth. Moreover, there is 
a more or less definite relation between the time required by a 
corn plant to reach the blossoming stage and the time required 
by it to reach full maturity. The former is usually not far from 
sixty per cent of the latter. In case of a large-eared variety, the 
period of blossoming to maturity is likely to be relatively longer 
than in case of a small-eared sort. For instance, the large-eared 
