272 DISEASES OF CROP-PLANTS 



Nature and Effects. 



The first stage of the disease exhibits a small rounded water- 

 soaked green spot on the surface of the boll. This extends at its 

 margin, while the tissues at the centre dry up and turn brown or 

 black. If the development of the lesion continues the carpel 

 is penetrated and the lint becomes thoroughly infested with 

 bacteria, including species which themselves are unable to attack 

 the boll, very commonly accompanied by one or other of the fungi 

 which readily occupy the original spot. A good deal of lint may 

 in this way be stained bright yellow, as in the internal boll disease, 

 or in severer cases completely blackened and rotted. Infections 

 at the base of the boll often involve the central column, while 

 those near the tip cause premature separation of the points of 

 the carpels and prevent complete separation when it is naturally 

 due. In both base and point infections more than one carpel 

 maj'' be affected, whereas spots on the face of the bolls usually 

 only affect the lock on which they occur. 



The development of the lesion may become arrested at any 

 stage, and under some circumstances this occurs before the lint 

 is reached ; the damage due to the disease is thus very variable 

 in amount. The appearance of the developed spots on the green 

 boll similarly varies. If they are infested with the pink anthrac- 

 nose fungus or the common similarly coloured Fusarium it is 

 identical with that familiar in figures and descriptions of anthrac- 

 nose injury ; if not so infected a somewhat sunken, dry, rough, 

 dark spot or patch, often with a water-soaked green margin, is 

 produced. 



In addition to the obvious injuries on developed boUs heavy 

 losses also occur from the shedding of flower buds and young 

 bolls infected at the base. 



Causation. 



From the very earliest appearances of the water-soaked spots 

 bacteria are present in the tissue in great numbers, and often 

 form a pale yellow transparent film on the surface of the spot. 

 The organism {Bacterium malvacearum E. F. Sm.) is identical 

 with that which gives rise to angular spot on the leaves. 



Mode of Infection. 



The spots are most often located either at the apex of the boll, 

 extending for a short distance down one side, or at the base near 

 to or under the calyx. They occur quite commonly however on 

 other parts of the surface, both between and on the suture lines. 

 Attempts to correlate the spots with bug punctures have revealed 

 no evidence of connection. 



The organism is commonly present on the plants in great 

 amount in connection with angular spot of the leaves and bracts. 

 When a plant so infected is thoroughly wetted by rain the bacteria 



