292 



BACTERIAL DISEASES OF PLANTS 



streaks; growth on gelatin; in Lo filer's solidified blood serum, 

 in Dunham's solution (see fig. 92.4). Does it cloud Dunham's 

 solution? Study behavior on potato. Hold the potatoes for 

 6 weeks and then test the substratum for destruction of starch, 

 mashing the cylinders in an abundance of distilled water (50 

 cc.) to which should then be added 2 cc. of alcohol iodine. Com- 

 pare with a mashed check cylinder of the steamed potato and 



FIG. 226. Cavities in a bean pod (outer part) due to introducing Bacterium 

 phaseoli by needle-pricks. Inoculated by the writer in 1897. 



with cultures of Nos. II and III. Has the potato lost its firm- 

 ness? Why? The progressive enzymic destruction of potato 

 starch (change from translucent, lustrous, bluish white to a dead 

 opaque white) may be watched from day to day if streaks are 

 made in test tubes on slant starch jelly. (For its preparation see 

 "Bacteria in Relation to Plant Diseases," Vol. I, pp. 50, 196.) 

 Determine action on milk and litmus milk. After some weeks' 



