410 BACTERIAL DISEASES OF PLANTS 



fuchsin. This stain gives sharp pictures of the bacteria but is 

 apt to overstain portions of the sections. Try amyl Gram, 

 which is very good. Can you devise a better single stain, or a 

 good double stain? 



Watch young leaves situated immediately above developing 

 stem tumors and if internal secondary growths occur along the 

 midrib, cut cross-sections of the petiole and of the stem below 

 it for presence of the channel of infection leading from the pri- 

 mary tumor. If you find it well-developed (as in Fig. 304), i.e., 

 as a tiny brown spot, cut also longitudinal sections involving 

 its path and make permanent stained preparations. Draw 

 some of the bacteria seen in it, together with the surrounding 

 parts. 



Is the tubercle corked over? Is there commonly a second- 

 ary fungous infestation? What other bacteria have you been 

 able to cultivate from natural tubercles? Can you isolate Schiff- 

 Georgini's spore-bearing bacillus (Consult Centralb. f. Bakt. 2 

 Abt., XV Bd., 1905, p. 198, and U. S. Dept. of Agric, B. P. 

 Ind. Bull. 131, Ft. IV, p. 38)? Berlese's yellow species? 



Variability. — All choice cultivated varieties of olives are 

 i-ubject to this disease, and the securing of a profitable resistant 

 sort is a work for the future. In Italy the Maremmano and Lec- 

 cino are rather resistant (Ferraris, 1915). In California Neva- 

 dillo bianco and Manzanillo are more subject to this disease 

 than the Mission olive. The greatest variability thus far ob- 

 served in this country has been that due to varying degrees of 

 cultivation and water-supply. As in pear blight, those infected 

 orchards that are well tilled and abundantly irrigated or liable 

 to heavy rainfall are most subject to this disease. Frequent 

 light rains are also favorable to the spread of the disease, per 

 contra dry situations and bright sunshine are unfavorable to it. 



Transmission. — It is generally believed in Italy that wounds 

 due to hail-stones favor the entrance of this organism, and also 

 those made at harvest-time by the peasants, who thresh the tall 

 straggling trees with poles to dislodge the olives. Observation 

 shows that the tubercles often originate in scars where leaves or 

 branches have been torn off. The reason for these various 

 wound-infections was unknown until Home, Parker and Daines 



