LEAF SPOTS. 507 



through the stomata. It is primarily a disease of the parenchyma, 

 but the vascular system is invaded ultimately. 



CAUSAL ORGANISM. Bacterium pruni Smith, is a small rod, motile by one to several 

 polar flagella. It grows readily upon the ordinary culture media. On agar, it resembles 

 Ps. campestris, producing a distinctly yellow pigment, but is distinguished by its feeble 

 growth on potato and by its growth in Uschinsky's solution, which is converted into a 

 viscid material like egg albumin. Gelatin liquefied slowly. Casein of milk precipitated 

 slowly and redissolved; litmus reduced but color restored later. No gas produced. 

 Thermal death-point 51. 



LEAF SPOT OF SUGAR BEET.* 



The sugar-beet leaves show dark brown, often black, irregular spots 

 on the petiole, midrib, and larger veins. The causal organism belongs 

 to the genus Pseudomonas; it has been described but not named. 



* Brown, Nellie A., Science, N. S., Vol. XXIX 753, p. 915, 1909. 



