294 



BACTERIAL DISEASES OF PLANTS 



Foe the disease. Signs. — After needle-prick inoculations 

 on young leaves, stems and pods, how long to first appearance 

 of the disease? Rate of progress of the infection. 



On sprayed plants how long before faint pale green dots can 

 be detected on the leaves (use hand lens and transmitted light, 

 examining every day)? How many additional days are re- 

 quired for these stomatal infections to become visible to the 

 naked eye by reflected light? How long before they become 

 conspicuous, forming definite, coalescing sunken spots? Have 

 you observed retention of the leaf-green around the bacterial 



spots and discharge of it in other 

 *" • parts of the leaf? How do you 



account for this? 

 •^ * Make similar observations on 



sprayed pods as to time of first 

 ■ appearance of spots, rate of prog- 

 ress, etc. Temperature has some- 

 m^f"^ • , thing to do with this, therefore 



■r •_ keep thermometric records. 



li 'V-'-- Describe the disease minutely, 



including its effect upon the pods 

 and its general effect upon the 

 plant. Are the roots ever dis- 

 eased? Are the pods dwarfed? 



Histology. — Study the manner 

 of entrance of the bacteria into 

 the bean-pod, employing very 

 young spots. Is it always stom- 

 atal? Is it generally so? In well- 

 developed spots on the pods, determine the manner of extrusion 

 of the bacteria. Is it always stomatal or may it be through rifts 

 in the tissues? (Sometimes the damp chamber may be of assis- 

 tance in determining this.) Still using the pods, make cross- 

 sections (free-hand and on the microtome) of spots in various 

 stages of development to determine what tissues are invaded by 

 the bacteria and how this invasion takes place. Make perma- 

 nent preparations. Young pods will cut much better than old 

 ones, but tissues of all parts, and of all plants, for that matter, will 



Fig. 227.— Flagellate rods of 

 Bacterium phaseoli. Idaho isola- 

 tion. Stained by van Ermengem's 

 silver nitrate method. Photomic- 

 rograph by the writer. X 1000. 



