274 BACTERIAL DISEASES OF PLANTS 



bouillon, milk, steamed potato, nutrient agar, etc. Inoculate 

 by needle punctures susceptible tubers (of more than one vari- 

 etjO and place one or more of each sort at the following tempera- 

 tures: 5°C., 8°C., 20°C., 30°C. Repeat if you are not satisfied. 

 What do you conclude? Is there any practical application? 

 If you have time, try also dry storage vs. damp storage at differ- 

 ent temperatures, inoculating as before. 



Select tubers of some variety whose flesh reddens or browns 

 quickly on exposure to the air, pare, grate quickly, squeeze the 

 juice at once through a cheese cloth into a narrow, tall jar, 

 divide into two equal portions, and steam one immediately 

 (to destroy the action of the oxidizing enzyme) ; allow the other 

 portion to oxidize freely in a shallow dish for 6 hours or more, 

 then steam. The two lots may now be tubed, re-sterilized and 

 comparative inoculations made, using, for each: a, one carefully 

 measured 1-mm. loop from a very young fluid culture; b, the least 

 quantity that can be withdrawn by dipping the end (if o centi- 

 meter) of a platinum needle into the culture fluid. Watch the 

 early stages of growth critically. What do you conclude? 



For the disease : (1) Signs. — What is the period of incuba- 

 tion — on stems of different ages? on tubers? Time between 

 local rot on the base of the inoculated shoots and a general ap- 

 pearance of disease? What changes occur in the foliage? How 

 soon after the above-ground signs do the tubers begin to rot? 

 This is best studied in the open field in summer and autumn. 

 Can the tops be destroyed without causing a rot of the tubers? 

 How do you account for this ? Is the brown or bllack stain ever ab- 

 sent from the stems when this organism is present? There is a 

 bacterial rot in which the brown stain is absent (Appel). To 

 what is this colorless rot due? Describe the disease. What 

 are the signs on the tomato? Try inoculating green tomato 

 fruits. Is it a common disease of the latter? Can other plants 

 be infected? Try all the plants that are rotted and not rotted 

 by Bacillus carotovorus. Study the flora of many naturally 

 rotting potatoes, especially the advancing margin of the rot, 

 for the presence of this organism. 



Histology. — Section diseased stems and tubers and make per- 

 manent mounts. Do the bacteria follow the vessels, or only 



