178 DISEASES OF CROP-PLANTS 



The disease has not been found in other palms with the 

 exception of a case in an unidentified species of Cocos. 



External Symptoms. 



The failure of the tree is marked by a progressive yellowing 

 and browning of the leaves in order of age, commencing at the tip 

 of each leaf reached in the process. Commonly the lowest living 

 leaves are the jfirst affected, but occasionally one or several 

 of these may remain green while the discoloration, commencing 

 above them, successively involves the younger leaves. In the 

 early stages the process is indistinguishable by external appear- 

 ances from the natural dying off of the old leaves, especially 

 where this is accelerated by drought, water-logging, or poor 

 conditions of growth in general. The difference becomes apparent 

 however from the steady march of the discoloration, which 

 soon begins to involve leaves in full vigour, and continues to 

 those in which the leaflets are not even fully expanded. A tree 

 at this stage is exceedingly conspicuous from its rich colouring 

 of brown, orange, and yellow, involving all but the central 

 tuft of young leaves. This condition may be reached in three 

 or four weeks from the time of appearance of the first symptoms. 



The shedding of green nuts in all stages of immaturity may 

 take place concurrently with or slightly in advance of the dis- 

 coloration of the leaves and is thus in some cases the first 

 external sign of trouble, though it must be remembered that 

 shedding of small nuts often occurs from healthy trees. 



Secondary infestation of the failing leaves with Diplodia sp. 

 results in the development of patches of brown or black rot, 

 wet but firm, in situations on the leaf-stalks, especially towards 

 the base. This appears to be the chief reason for the tendency 

 of the leaves to break across and hang down. Such infestations 

 are common in healthy trees on leaves approaching senility, 

 but have much more scope when the leaves are failing in rapid 

 succession from disease. 



In the final stage of the disease there ensues a bacterial 

 soft rot of the tender tissues forming the apex of the stem, as 

 also of the similar tissues at the base of the young inflorescences. 

 There is no connection between this and infectious bud-rot 

 disease : death of the coconut palm from widely differing causes 

 is regularly followed by bacterial putrefaction of the enclosed 

 soft tissues of the bud. 



Internal Symptoms. 



The following description applies to trees during the process 

 of failure of the leaves before the secondary rotting of the bud 

 begins. A cross section towards the base of the stem shows a 

 well-marked zone, usually i-i^ inches wide and beginning 1-2 

 inches from the periphery, in which the ground tissue is dull red 



