310 The Philippine Journal of Science 1922 
have further been shown to cause the leaves of grapefruit to’ be 
more permeable to water than are those of the more canker- 
resistant mandarin orange.’ It was also demonstrated in an- 
other paper that water could be forced through the uninjured 
stomata of grapefruit by the application of comparatively little 
pressure. 
The above-mentioned studies strongly suggested that the 
differences in structure of the stomata and permeability of the 
leaves of mandarin and grapefruit are responsible for the resist- 
ance to canker of the former and the susceptibility of the latter. 
At this stage of the investigations it seemed desirable to at- 
tempt by some means to introduce the canker bacteria within 
the leaf tissue of the resistant mandarin orange variety with- 
out mechanical injury; if canker resulted it would be apparent 
that the tissues were not dependent on injury to render them 
susceptible. Moreover, the development of canker lesions on 
this host, after withdrawing the air from the stomata, would 
substantiate the theory that it is the peculiar structure of 
the stomata in the leaves of the mandarin orange that con- 
tributes to resistance. 
In the study here reported, a method has been devised for 
drawing water into intact leaves on the tree in the orchard, by 
the use of known and easily measurable pressure. Canker has 
been produced in young leaves of the mandarin orange, grape- 
fruit, and pummelo by substituting an infusion of Pseudomonas 
citri Hasse for the water. The experiments are described in the 
following paragraphs. 
APPARATUS AND PROCEDURE 
The device used to force water and canker organisms into the 
citrus leaves was an adaptation of the porometer.* It consisted 
of a suction tube with a rubber lip for pressing against the leaf, 
a mercury pressure gauge connected with it to indicate the 
reduced pressure in the suction tube, and a simple aspirator, 
also connected with the suction system, the rate of withdrawal 
*McLean, Forman T., The permeability of Citrus leaves to water, 
Philip. Journ, Sci, 19 (1921) 115-123. 
‘Darwin, F., and Pertz, D. F. M., A new method of estimating the 
aperture of stomata, Proc. Roy. Soc. London, Ser. B, No. B569 (1911) 
136-154; Trelease, Sam F., and Livingston, B. E., The daily march of 
transpiring power as indicated by the porometer and by standardized hy- 
grometric paper, Journ. Ecol. No. 1 4 (March 1916) 1, abs. in Science New 
Ser. 43 (1916) 363, 
