34 



THE FUNGI WHICH CAUSE PLANT DISEASE 



From swellings known as olive tubercles on Califomian olive 

 branches, E. F. Smith isolated this organism*' which is in part 

 Ps. oleae-tuberculosis and which may bear relation to several other 

 olive bacteria previously described in Europe. 



The organism when inoculated by puncture into young olive 

 shoots produced the characteristic tubercle. Later it was re- 

 isolated from these artificially produced tubercles and used in a 

 second series of inoculations which gave a second crop of tubercles. 

 Controls showed no infection and healed promptly. The oleander 

 was not susceptible to infection. 



Smith's results are not in full accord with much of the European 



work on the olive tubercle. 



Ps. sesami Malk. causes disease on sesame ^. 



Ps. stewarti, E. F. Sm. A medium size rod, 0.5 - 0.9 ju x 1 - 2 fi, 



with rounded ends, and 1 polar fiagellum. Buff-yellow to chrome 



or ochre color; non-liquefying; does not separate casein in milk. 



T. D. P. 10 min., 53°. 

 Agar colonies subcir- 

 cular, becoming lobate; 

 bouillon rendered tur- 

 bid with yellow-white 

 precipitate. No gas. 



The bacterial com 

 blight of this organism 

 was first described by 

 Stewart in 1897 " and 

 attributed to bacteria. 

 The organism was de- 

 scribed by E. F. Smith 

 in 1890 «» from a cul- 

 ture furnished by Stew- 

 art. Definite proof by 

 the 

 causal relation of this 

 particular organism to the disease was adduced in 1902 by 

 sprinkling bacteria upon the leaves.ss-™ Some plants showed 

 typical constitutional symptoms during the first month, most of 

 them in two or three months when the plants were several feet 



Fig. 21. — Various forms of Ps. stewarti, grown on 



potato agar; a and b are typical forms. After inoculation of 



