i88 
Walter Stiles and Ingvar Jorgensen. 
general activities of the plant. Flower and fruit formation, or even 
final yield of vegetative material, do not necessarily follow the total 
increase in growth after an arbitrary time. Such statical methods 
have caused the drawing of wrong conclusions in other branches of 
plant physiology. 
On the other hand the measurement of dry weight is much to 
he preferred to the measurement of fresh weight, which is subjected 
to all the drawbacks of the measurement of dry weight and to this 
as well, that the fresh weight will vary during the day according to 
the rate of transpiration. 
7. The accuracy of the results obtained in the Water Culture 
Method. The differences which may result on account of hereditary 
factors and on account of unsuspected differences in environmental 
factors during germination and later stages of the life of the plant, 
make it necessary to determine the degree of accuracy of the 
results obtained. The vast majority of the results obtained by the 
water culture method are absolutely valueless as no probable errors 
of experiment are calculated, and the results are given in such a 
form that it is impossible to calculate them. Often differences 
regarded by the investigators themselves as significant are obviously 
not so. 
We would emphasize again, as formerly, the necessity of 
calculating the probable error of experiment when water cultures 
are used, as only in this way can the significance of obtained 
differences be appreciated. 
The Present Experiments. 
The question with which we deal particularly in this paper is 
that of aeration of the culture solution, a question which has received 
some attention in recent years. Thus Hall, Brenchley and 
Underwood (5) record greatly increased growth as measured by dry 
weight as a result of continuous aeration of the solution. 
Their conclusions were obtained with Barley and Lupin grown in 
sets of four. Their results are shown in the accompanying table. 
% 
Aerated 
Aerated 
Not aerated. 
continuously. 
once a day. 
Barley 
Lupin 
. 
2-122 
1-53 
0-72 
1-314 
0'83 
The increase is striking and greater than differences due to 
experimental error, as can be calculated from the data of the 
weights of individual plants recorded in the paper. 
