116 The Philippine Journal of Science 1921 
surface tension than water, such as alchohol, benzol, etc., was 
employed by Molisch ? as an index of the openness of the stomata. 
He studied the rate of infiltration of these liquids without em- 
ploying pressure, and found that water was unsuitable for his 
purpose. 
The study here reported was undertaken to ascertain what 
pressures are necessary to cause infiltration of water through 
the stomata of Citrus leaves. A satisfactory method of causing 
water to enter the leaves through the stomata and of observ- 
ing the place and manner of entrance was devised and is here 
described. It was also found that penetration of water through 
the stomata can be easily induced under certain conditions, and 
that there are apparently differences in the amount of pressure 
required to cause penetration into the leaves of different varieties. 
Three varieties of Citrus were used in these tests: Washington 
navel orange, Szinkom mandarin orange, and Pernambuco grape- 
fruit. 
APPARATUS 
The equipment employed is shown in figure 1. It consists 
of a flat gas chamber g c of metal with a tube connection at 
each end. The bottom is of glass ; the metal top has a circular 
aperture in it about 1.5 centimeters in diameter, over which the 
leaf 1 is placed. The gas chamber is mounted on the stage of a 
compound microscrope m, in position to examine the leaf sur- 
face under the low power (16-millimeter objective). The right- 
hand tube of the gas chamber is connected to a mercury pressure 
gauge p, which is fitted with a scale s and mirror n to facilitate 
the rapid reading of the height of the mercury column by the ob- 
server seated at the microscope. The left-hand tube of the gas 
chamber is attached to an aspirator é, arranged to draw air 
from the gas chamber, the rate being controlled by means of the 
valve v. 
PROCEDURE 
A piece of convenient size, usually about 3 centimeters in diam- 
eter, was cut from the leaf to be tested, and the upper epider- 
mis and palisade tissues were shaved off with a sharp razor 
from a small area in the center about 2 millimeters in diameter. 
Then the cut outer edges of the leaf were coated with paraffin 
(melting point, 45° C.), and it was then sealed on to the aper- 
ture of the gas chamber with paraffin, the intact lower surface 
* Molisch, H., Opening and closure of stomata as shown by the method of 
infiltration, Zeitschr. Bot. 4 (1912) 106-122, 
