222 
GENETICS: PEARL AND SURFACE 
cal properties of the follicle membrane that might readily occur under 
ordinary conditions. These questions will be discussed in the full ac- 
count of the work to be published in the Archiv fur Zellforschung. 
GROWTH AND VARIATION IN MAIZE 
By Raymond Pearl and Frank M. Surface 
BIOLOGICAL LABORATORY, MAINE AGRICULTURAL EXPERIMENT STATION 
Presented to the Academy, February 23, 1915 
The Problem. The investigation reported in this paper is an attempt 
to analyze the normal variation of an organism in a particular case, 
from the standpoint of Entwicklungsmechanik. It was suggested in the 
first instance by the study of variation and differentiation in Cerato- 
phyllum made by Pearl some years ago. We have here attempted to 
approach the problem of m/e/'-individual variation from the same point 
of view and with similar methods to those applied to the problem of 
iw/m-in dividual variation in the case of Ceratophyllum. 
The problem and the point of view may be most clearly defined by 
considering briefly certain well-known, indeed obvious, facts about vari- 
ation. If one brings together a homogeneous group of individual plants 
or animals and measures the same character in each individual, there 
may be formed from the resulting data a characteristic variation curve 
for that group and character. The precise form of this curve, as well 
as the location in it of any particular individual, are functions of two 
basic variables. Of these one is the hereditary or germinal constitution 
of the individual. The other is the complex of environmental stresses 
and strains, which, each acting on the individual during its ontogeny 
have influenced the end result of the activity of the hereditary deter- 
miners or genes. 
Now it is altogether usual in discussions of variation and heredity to 
take the two end terms of the ontogenetic series, the gene on the one 
hand and the adult soma on the other hand, as things given. What 
comes between the two is neglected. But clearly what goes between is 
a part of the very essence of heredity itself. 
In any group of adult individuals each one will show some particular 
variation, in the sense of a deviation from the typical condition of the 
group. We take it to be one of the final objects of investigations in 
genetics to find out why (in the sense of locating the essential causal 
factors involved) a particular individual A exhibits a particular varia- 
tion a, and not some other variation out of the indefinitely large number 
