118 The Philippine Journal of Science 1921 
of the leaf uppermost and the shaved thin portion in the center 
of the aperture. A glass ring was then fastened over the leaf 
with paraffin, and the small reservoir formed by the leaf and 
the glass ring was filled with tap water and covered with a mi- 
croscopic cover glass. The gas chamber was then connected with 
the pressure gauge and aspirator, and the leaf surface under 
water was examined with the low power of the microscope 
(16-millimeter objective) before any air was withdrawn from 
the gas chamber. In all cases the thinned portion of the leaf 
appeared opaque, due to the presence of air in the intercellular 
spaces, expect at the spots over oil glands, which were trans- 
lucent. The stomata had their outer chambers filled with large 
air bubbles. . 
Air was then gradually withdrawn from the gas chamber un- 
der the leaf section by means of the aspirator. The partial vac- 
uum in the chamber and consequent pull on the water tending 
to draw it into the leaf tissues were indicated by the height of 
the mercury in the pressure gauge. The condition of the leaf 
was closely watched meanwhile, until the appearance of new 
translucent spots indicated that the leaf tissues were flooded, or 
until drops of water were observed by their shadows to be form- 
ing on the thinned pertion of the leaf. Then the height of the 
mercury in the pressure gauge was recorded, the water reservoir 
was removed from the leaf, and the portions where water pene- 
tration had occurred were carefully examined. Actual breaks in 
the epidermis were observed in only two cases, and both of these 
were due to rapid and excessive application of pressure to the 
leaf. These two tests were valueless and were therefore dis- 
carded. In most cases it was clear, from the slow rate of infil- 
tration and from subsequent examination of the spot where the 
water had entered, that it had entered through the intact stomata. 
An effort was made to locate the particular stoma through 
which it first penetrated, but this could not be clearly distin- 
guished because of the low magnification, and in several cases 
the penetration first occurred through the thick tissues at the 
edge of the thinned portion, where the stomata could not be 
clearly seen. While examining the flooded portions of the leaf, 
a few measurements of the width of the ridge of entrance of 
the larger stomata in this portion were made, because the width 
of the stomatal aperture is thought to be the controlling factor 
in preventing the entrance of water. 5 
It was necessary to bring the leaves from the field to the labor- 
atory for testing, and it was found that the preliminary treat- 
