[Vor. 1 
8 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
larly important that each experiment should be carefully ex- 
amined prior to making all readings. The water columns 
in the burettes were so gauged as to eliminate the possibility 
of forcing water into the leaves. Тһе burettes were employed 
solely in order to get accurate readings of the water loss from 
hour to hour without shifting or disturbing the plants by weigh- 
ing; also rapidly to get data, should it seem necessary, under 
changing conditions. АП of these considerations proved very 
important, as it was found that a slight shifting of the position 
of the leaf affected materially the transpiration magnitudes. 
For each leaf used it was necessary to get its rate of transpira- 
tion in terms of some standard in order that the ratios might 
be established between certain leaves prior to the addition 
of the spray to some of them and the ratio between the same 
leaves after the applieation. At one time it seemed possible 
that the revolving table method of standardizing porous сарв 
might be applicable, but on further consideration it was believed 
that the use of this method in the laboratory, and the subse- 
quent disposition of the plants in the open, would lead to errors 
of considerable magnitude. For our purpose it was not consid- 
ered desirable to conduct the whole experiment on the revolving 
table, but this method will be employed in connection with 
our further studies. It was found very important to standardize 
the leaf in a given position and then permit it to remain in 
that position, as far as possible, throughout the experiment. 
This method was necessary largely because of the fact that it 
seemed wise to conduct the experiment in the open, during a 
considerable interval, at least. Further reference to the ar- 
rangement of the plants will be made in the discussion of the 
experimental work. 
Experiments with potted plants.—For the experiments with 
potted plants tomatoes were used. The pots were dipped in 
paraffin wax and the same sealing mixture was coated over 
the surface of the soil. In all the experiments reported there 
was no leakage in any case from improper sealing. Water 
was added daily, or twice a day, to supply the loss by trans- 
piration, the addition of water being made by means of a thistle 
tube fixed in each pot. The bell of the thistle tube was covered 
with paraffined paper during the entire interval. It was also 
