THE OLIVE tubercle: TRANSMISSION 411 



ill California showed that under the action of rain the tubercles 

 ooze bacteria freely to their surface from whence they are washed 

 to other parts of the tree. They conclude that: ''The infected 

 trees must be covered during the rainy weather of winter with 

 an almost continuous coating of the specific bacteria." Prob- 

 ably birds and insects also help to spread the disease, but exact 

 experiments, so far as I know, are wanting. Petri in Italy has 

 shown, however, if not absolutely at least with a fair degree of 

 conclusiveness, that the olive fly, Dacus oleae, carries this organ- 

 ism along with the yellow bacillus {Ascobacterium luteum Babes) 

 in its salivary gland and intestinal diverticula as a regular 

 (symbiotic) occupant (vide Centralh. f. Bakt. 2 Abt., XXVI 

 Bd., p. 357, and more especially ''Ricerche sopra i batteri intes- 

 tinali della Mosca olearia," Memorie d. r. staz. di patologia vege- 

 tale, Roma, 1909, from which also I have taken various accredited 

 citations under Cultural Characters, etc.). The second organ- 

 ism mentioned is the yellow saprophyte so often found in the 

 olive tubercle. Also as in pear blight, it is likely that the dis- 

 ease is sometimes spread by pruning instruments, and certainly 

 it must be brought into the orchard frequently from the nursery. 

 In California during the dry summer season no new infections 

 occur but with the coming on of winter rains and of spring rains 

 infections are numerous. Home and his colleagues believe that 

 infections take place without insect wounds, by growth of the 

 bacteria in bark crevices from which they penetrate the deeper 

 tissues especially over places subject to tension from rapid 

 internal growth, and that varieties with a smooth bark and an 

 open habit of growth like the Mission olive are, for these reasons, 

 freer from the disease than those having a rough bark and a more 

 compact habit of growth. 



LITERATURE 



Read: (1) Smith, Erwin F., ''The OUve Tubercle," Science, 

 N.S., Vol. XIX, p. 416, March 11, 1904; (2) Do. " Some Observa- 

 tions on the Biology of the Olive-Tubercle Organism," Ce7i- 

 tralblatt fiir Bakteriologie, etc., 2 Abt., XV Bd., 1905, p. 198; 

 (3) Do. "Recent Studies of the Olive-Tubercle Organism," 

 Bull. 131, pt. IV, Bureau of Plant Industry, U. S. Dept. Agri- 



