S. a. Patne AM) II. Stansfield 35 



turing the leaf, and by gently rubbing with the finger a water suspension 

 of the organism upon the upper surface of the leaf. Except in one case 

 typical disease resulted from these experiments. Control experiments 

 were made with heated bacterial slime and with a gum arabic solution 

 brought to the opacity of the slime with potato starch. The object of 

 these controls was to determine whether physiological influences, such 

 as the blocking of the stomata or the local shading from light of the 

 tissue, would produce the symptoms of disease. None of these controls 

 showed any browning effect. The brown substance however is formed 

 in response to wounding round the needle pricks in control experi- 

 ments but, as seen in Plate II, Fig. 2, there is a marked difference 

 in the extent of discolouration between the infection and the control 

 spots. 



The fact that infection could be produced by gently rubbing a suspen- 

 sion of the organism over the surface of the leaf would suggest that the 

 mode of entry of the bacteria into the leaf under natural conditions is 

 by way of the stomata. In accordance with the xerophytic habit of the 

 plant the cuticle of the leaf, which is exceedingly thick, is raised above 

 the guard cells of the stoma in the form of a spacious cup (Fig. 4) 

 eminently suited to catch water and act as a port of entry for bacteria 

 to the chamber below. The spots always appear to have developed in 

 connection with the stomata, and in a large number of cases a single 

 stoma has been found occupying the very centre of the surface of the 

 diseased area, though no sections of diseased spots have revealed the 

 presence of bacteria in either the stoma itself or in the sub-stomatal 

 chamber. 



Description op the Causal Organism. 



(i) MorpJiological Characters. 



Form and Size. The organism taken from an agar slope incubated 

 for 24 hours at 22° C. is a small oval rod 0-8-l-6^ x O-Q-O-Sfj,; pairs up 

 to 2-5/Lt X 0-8fx. In sections of diseased spots where organisms can be 

 found they appear to be of about the same diameter but almost coccoid 

 in form. 



Motiliiij. In young cultures the organism is actively motile with a 

 free swimming motion. The flagella stain quite readily by the method 

 of van Ermengen and a beautiful preparation was obtained by the 

 method of PHmmer as yet unpublished^; they are from one to three in 



1 It is hoped that the pubUcation of this method will not be long delayed. 



3—2 



