CHAPTER III. 

 LEAF SPOTS. 



SPOT or THE LARKSPUR. 

 Bacillus delphini Erw. Smith. 



So far as is known, this disease occurs only on the larkspurs of Massa- 

 chusetts. Infection takes place through the stomata, resulting in numer- 

 ous black spots on the leaves and stems. 



CAUSAL ORGANISM. Smith* describes the organism as a motile, gray-white, non- 

 liquefying, nitrate reducing bacillus. Agar colony has characteristic wrinkled structure. 

 Grows in Uschinsky's solution. No growth at 37; thermal death-point 48 to 49. i. 



BACTERIAL SPOT or PLUM AND PEACH. 



Pseudomonas pruni Erw. Smith. 



The first occurrence of the bacterial spot was reported on the Japanese 

 plum in Michigan. { Later, what appeared to be the same disease was 

 observed on the peach in Georgia | and Connecticut, and more recently 

 it has been found throughout the South and Middle West. 



SYMPTOMS. On the plum, the leaves and green fruit exhibit nu- 

 merous small, water-soaked spots; later the diseased tissue of the leaves 

 falls out, giving a shot-hole appearance, and the plums show black, 

 sunken areas and deep cracks. The spots may reach a diameter of 

 one-fourth to one-half inch. 



On the peach leaves, angular, purplish-brown spots one-eighth 

 to one-fourth inch in diameter are formed, which drop out giving the 

 shot-hole effect. The organism also attacks the young twigs and fruit. 

 It destroys the bark of the former, producing black, sunken areas, while 

 on the latter it causes small purplish spots over which the skin cracks. 



In both the plum and the peach, infection is believed to take place 



* Smith, Erw. P., Science, N. S. Vol. XIX, No. 480, p. 418, 1904. 

 t Smith, Erw., Science, N. S., Vol. XVIII, 429, p. 456, 1903. 

 J Rorer, J. B., Science, N. S., Vol. XXIX, 753, p. 914, 1909. 



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