Transpiration as a Factor in Crop Production. 41 
PART II. THE EXPERIMENTS. 
The investigations which follow have been conducted at the 
Agricultural Experiment Station of Nebraska, Lincoln, Nebr. 
Most of the data have been secured during the last three years 
(1912-1914) and have not been published before. In some 
instances earlier work at this Station has been continued along 
similar lines or extended, in which case the related data have 
been reproduced here, and reference given to the earlier pub- 
lications. 
PROBLEMS UNDER INVESTIGATION. 
The general project has been to study the relation of environ- 
mental factors and plant characters to the water requirements of 
crops. Under environment, climatic factors, soil fertility, and 
soil moisture have been investigated. Evaporation from a free 
water surface, as a summary expression of the various climatic 
factors, has been studied at different elevations in corn and 
small-grain fields. Concerning plant characters a number of 
measurements have been made of all plants tested, in order to 
observe any possible correlation. During one year (1914) the 
relative water requirements were determined of corn secured 
from humid and semiarid districts, of corn varieties differing in 
growth habits, and of a number of sorghum varieties and sun- 
flowers in comparison with corn. Histological studies were made 
to determine whether there may be any structural correlations. 
Ash determinations were made for studying the relation between 
transpiration and the intake of soil solutes. 
Thus, it is seen that all the investigations, with the exception 
of 1914, have been made with corn. It is believed that in this 
way general principles concerning transpiration may be established 
which will apply not only to corn, but to many other crops as well. 
In connection with the general project, possible sources of ex- 
perimental error have been investigated. 
METHODS OF COMPILING DATA. 
The data contained in the following general tables consist 
of two distinct kinds, namely, (1) exact quantitative measurements 
and (2) ratios between these exact measurements. To illustrate 
by referring to Table 4, columns 2, 3, 4, 5, 6, 7, and 13 are exact 
measurements, while columns 8, 9, 10, 11, and 12 are ratios. 
It is important to understand the manner of compiling the average 
data for the duplicate potometers. Those columns in the tables 
which contain exact quantitative measurements are averaged by 
adding the column and dividing by the number of duplicates. 
