108 
Research Bulletin Xo. 2 
genetic or physiological, between duration of growth and inter- 
node length. There is also little or no physiological correlation 
between duration of growth and number of nodes, but appar 
ently a distinct genetic correlation between these two characters. 
In 1 Oil. families of corn, which from previous selling were ap- 
proaching a condition of homozygosis of factors for size and 
duration of growth, showed a slight negative correlation between 
number of nodes and duration of growth, while F 2 families, 
heterozygous for both number of nodes and for duration of 
growth, showed a marked positive correlation between these 
characters. If height of stalk alone had been considered instead 
of number of nodes and internode length, it might have been 
thought, in case of these F 2 families, that the unfavorable 
weather of early summer, by checking the growth of the early 
plants, and the favorable weather of late summer, by in- 
creasing the growth of the late plants, had brought about an 
apparent rather than a real correlation. But since the number 
of nodes is determined before the plant has made much growth, 
this character could not have been influenced by the differences 
between the weather of early and that of late summer. It is not 
that one set of conditions made the early plants have few nodes 
and another set made the late plants have many nodes, but 
rather that some of the genetic factors that caused the plants to 
have a large number of nodes were associated with the factors 
(or were themselves the factors'! that caused prolonged growth. 
It is expected that the detailed evidence upon which this con- 
clusion is based will be prepared for publication in the near 
future. 
The interrelations of such characters as number of rows per 
ear, circumference of ear, and breadth of seeds are obvious. An 
ear, of course, could not have many rows and a small circumfer- 
ence without having very narrow seeds. But this and similar 
relations are in the main mere mechanical adjustments rather 
than physiological — to say nothing of genetic — correlations. 
It is often impossible to tell in a particular case whether 
distinct factors are coupled in inheritance or whether a single 
factor plays a part in the development of what are regarded as 
distinct characters. In the latter case the problem is funda- 
mentally one of the physiology of development rather than of 
genetics. 
Certain quantitative relations in maize illustrate the influ- 
ence of a single factor in the development of two or more char- 
acters ;is well :is the influence of several factors in the develop- 
ment of a single character. It is obvious that any factor that 
affects say internode length will also have an influence upon 
