6 14 MICROBIAL DISEASES OF PLANTS 



nutrient broth moderate clouding occurs, and a membranous pellicle is formed 

 which breaks readily on shaking. On potato, the growth is slimy, shining, creamy- 

 white. Plain milk clears slowly without coagulation, becoming translucent and 

 tawny-olive with age. Lavender-colpred litmus milk is completely blued in three 

 days, and a creamy-white pellicle is formed at the surface; clearing is complete in 

 twenty days, and later the blue color bleaches out leaving the fluid a translucent 

 browui 



The organism grows in Uschinsky's, Fermi's, and Cohn's solutions producing a 

 green coloration in the first two. 



No gas is formed from the ordinary sugars; acid is produced from saccharose 

 and dextrose. Nitrates are not reduced. Hydrogen sulphid is not formed. A 

 small amount of indol is produced in 2 per cent peptone water and peptonized 

 Uschinsky's solution. Methylene blue in milk is rapidly reduced. The organism 

 is an obligate aerobe. 



Optimum temperature is 25° to 27°.; no growth at 36°. 



Method of Infection. — ^The causal organism enters the leaves 

 through the stomata, no wounds being necessary. 



Control. — Laboratory experiments upon the germicidal action of 

 copper sulphate on Ps. lachrymans suggest that Bordeaux mixture^ 

 properly applied, may be a remedy for the disease. 



Spot op the Larkspur 

 Bacillus delphini — Erw. Smith 



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

 Massachusetts. Infection takes place through the stomata, resulting 

 in numerous 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 49.1°. 



Bacterial Spot op Pltjm and Peach 



Fseudomonas pruni — Erw. Smith 



The first occurrence of the bacterial spot was reported on the Japan- 

 ese plum in Michigan, t Later, what appeared to be the same disease 

 was observed on the peach in GeorgiaJ and Connecticut, and more 

 recently it has been found throughout the South and Middle West. 



• Smith, Erw. P., Science, N. S., Vol. XIX, No. 480, p. 418, 1004. 

 t Smith, Erw., Science, N. S., Vol. XVIII, 42p, p. 456, 1903. 

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



