32 THE FUNGI WHICH CAUSE PLANT DISEASE 



Ps. pruni, E. F. Sm. The organism resembles Ps. campestris 

 but is distinguished from it by its feebler growth on potato and 

 by its behavior in Uschnisky's solution which it converts into a 

 viscid fluid. It consists of small rods, motile by one to several 

 polar flagella. T. D. P. 51°. Gelatine not liquefied. Casein 

 slowly precipitated and later redissolved. No gas. 



The bacteria enter through the stomata of the Japanese plum; ^^ 

 cause small watery spots on green fruit and leaves, and finally the 



FiQ. 19. — Earliest stage of fruit spot on green plums, due to Ps. 

 pruni. The bacteria entered through the stoma. After Smith. 



death of the affected tissue. In earliest disease they are limited 

 to the substomatal space but gradually they invade more distant 

 tissue. Wounds are not necessary to infection. It seems to have 

 been seen first on the peach in 1903 by O'Gara in Georgia and in 

 the same year by Clinton in Connecticut. Rorer *' by numerous 

 cultures and cross inoculations proved this same organism re- 

 sponsible for a leaf, twig and fruit disease of peaches. In the twig 

 the bacteria were present in great numbers in the bast. 

 Ps. radicicola (Bey.) Moore.** The legume root-tubercle or- 



