PLANTS SUBJECT TO MICROBIAL DISEASES 293 



the sterile stiff needle for control and place in a sterile 

 deep culture dish. 



5. Obtaining some of the culture of B. carotovorus on 

 the sterile needle, puncture the remaining vegetables in the 

 center of the disinfected area and place vegetables in a 

 sterile deep culture dish at 20 to 25 C. 



B. carotovorus is a wound parasite which invades the 

 intercellular spaces, dissolving the middle lamellae and 

 portions of the inner lamellae, thereby establishing a con- 

 dition which is known as soft rot. 



6. Examine in twenty-four hours for evidence of action 

 of B. carotovorus. This should be easily distinguishable 

 in three days. 



7. Isolate the causal organism and determine its mor- 

 phology and cultural characteristics. Compare with pure 

 culture and with description given in Marshall's Micro- 

 biology, p. 512. 



Is the organism newly isolated, capable of producing 

 infection? Make inoculations from one, two, three and 

 four-day old newly isolated cultures to sterile living vege- 

 table tissue to determine this. Is there any difference in 

 the infectivity of a one-day old and a three- or four-day old 

 culture? 



8. What is known of methods of control of this disease? 



9. Grow four giant colonies of B. carotovorus on ordinary 

 agar, one in each Petri dish and allow them to develop 

 until nearly 1 cm. in diameter. 



10. Under sterile conditions, remove slices of fresh 

 carrot, beet and rutabaga or turnip roots and potato and 

 place in sterile Petri dishes. (Slices should be at least 

 3 to 4 cm. in diameter.) 



11. With a sterile scalpel make a circular incision 0.5 

 cm. from the edge of the colony through the layer of agar 

 in the Petri dish. 



12. Remove this colony intact to the surface of one of 

 the slices of vegetable and replace cover of Petri dish. 



