Jan., 1922] PULLING — BIOPHYSICS IN PLANT PHYSIOLOGY 
43 
the distribution of characters is so ordered that by plotting numbers of 
individuals with a like magnitude of activity-intensity under a given set of 
conditions as ordinates and the corresponding magnitudes as abscissas, 
a curve of distribution will be obtained, a curve which has a form charac- 
teristic of the kind of activity considered and which will be unchanged by 
incorporating data derived from other individuals, if a sufficiently large 
number were considered in the first place. If, instead of the magnitude of 
an activity, the magnitude of the constant were thus to be plotted, there is 
every assurance that a curve of characteristic form would similarly be 
produced and, moreover, the value of the constant for the average individual 
could thus be determined. Naturally a sufficiently large number of in- 
dividuals must be investigated, but the difficulties would be less than they 
now are for statistical investigation of the effect of environment upon plants, 
for the experiments need not be performed upon all the plants at the same 
time. As a matter of fact, they need not be performed under precisely the 
same experimental conditions, for, within limits of course, the constant 
characterizes the plant under all external conditions without change. 
In this lies a further great advantage that will accrue to physiology. 
Many experiments of fundamental importance to the science are not begun 
because of the virtual impossibility of performing difficult or tedious opera- 
tions upon a sufficiently large number of plants. In other experiments the 
mere collection of the required data destroys the plant. If the proper 
relations of the kind we are discussing were known for the physiological 
processes under consideration by an experimenter, many of the difficulties 
that hamper him would vanish. A few plants operated upon in the de- 
sired fashion would yield data that in conjunction with our plant constant 
would permit the extension of the conclusions to the average plant or to 
any individual whose constant was known. Plants need not be destroyed 
to ascertain the progress of some process not accessible to direct observation 
in the living plant, for successive measurements of a change in the externally 
manifested variables would permit the calculation of the corresponding 
changes in the internal activity. 
It will be promptly objected that one of the outstanding characteristics 
of plants is their ability to alter their habit of living, to become really dif- 
ferent systems, and hence to change their constants. This is actually an 
argument for undertaking the determination of these constants, because, 
whether the constant turns out to be useful or not in practical experimenta- 
tion, this question of the degree of stability of inherited characteristics is 
fundamental to a unified science. At present plant physiology is much in 
the condition of chemistry before the discovery of combining weights: no 
theoretically valuable, quantitative experimentation was possible. Without 
question the greatest handicap under which plant physiology — and all 
biology — labors is the inability of the experimenter to evaluate the organism 
with which he works. 
