108 PROTECTION OK PLANTS — 1922-23 



Symptoms of the disease. 



As far as the writer has been able to observe, the infection and rotting of 

 parts of the plants make take place at any time during the growing season when- 

 ever conditions are favourable for the growth of the parasite. Specimens of 

 newly infected shoots were collected from early spring until as late as October 

 9th. 



The disease is first noticeable in the field by the presence of leaves with 

 wilted tips. A closer examination of the shoots shows that they are slightly 

 dwarfed as compared with the healthy parts of the plant. Conditions made it 

 impossible to obtain an illustration of this fact from plants growing in the field. 

 The writer, however, transplanted both diseased and healthy shoots from the 

 same plants, and after placing them in the greenhouse under the same condi- 

 tions, watched their development. After five months the diseased plant was 

 extremely dwarfed while the healthy specimen appeared quite normal. 



After the tips of the leaves die back, the basal portions commence to show 

 watersoaked areas. This watersoaking, which is due to the breaking down of 

 the cells, progresses up the leaf until the latter becomes limp and collapses. The 

 disease sp'reads from the centre of first infected shoot, upwards, until finally, 

 after a period of frbm 7 to 10 days from when the first symptoms are noticed, 

 the entire shoot becomes wilted. After the leaves have collapsed, there is often 

 a bacterialooze of a dirty cream colour, which exudes from the base of the shoot 

 just above the ground. Once the shoot has become wilted, it is only a short 

 time till it becomes dried, turns brown, and entirely shrivels up. 



In the greenhouse, when plants are kept under bell jars and then artifi- 

 cally inoculated, the symptoms are slightly different, due to the fact that the 

 rotting takes place much more rapidly. In one case an artificially inoculated 

 plant which was growing in sterile sand became entirely wilted for days after 

 inoculation. In a case such as this, there is no apparent dwarfing or wilting of 

 the leaf tips, otherwise the appearance of the disease is similar to that in the 

 field. 



In the rhizome the first visible sign is a slight darkened area around the 

 point of infection. This gradually increases until the entire young part of the 

 rhizome has become infected. An examination of the infected part will show 

 the rhizome tissues to be soft and of a thick slimy consistency, as compared 

 with the firm turgid condition of the normal tissue. In a short time the whole 

 infected part will be reduced to a soft, slimy, dirty-gray mass, swarming with 

 the bacteria and emitting a stong unpleasant odour. As the disease progresses 

 in the rhizome, this soft rotten mass gradually loses its moist consistency, be- 



