236 



light colour; another reason why the fibres show up clearly 

 in disease is the fact that the intervening tissue soon 

 sinks in somewhat (flg. 1 at a). In the dead bark this 

 sinking in has become much more marked, so that the 

 fibres stand out still more; this phenomenon, however, 

 also takes place in branches which hâve died from other 

 causes, and one may therefore not assume, in examining 

 the dead branches, that they hâve died of the die-back 

 disease. 



The discoloration of the bark may be best observed by 

 cutting off a pièce of it longitudinally. Not only the bark, 

 but the wood also undergoes a change of colour, which 

 is especially clear in transverse section ; the diseased por- 

 tion of the wood, while still alive, acquires a pale brown 

 colour which after death changes to dark grey. If only a 

 portion of the branch is attacked — a common case, 

 wliich has already been described above — ■ it becomes 

 évident on transverse section of the branch, after the 

 death of the diseased portion, that the change in co- 

 lour extends to the centre of the wood along a definite 

 sector. In Fig. 2 the dark sector represents the dead por- 

 tion of the branch. 



On the dead branches in the field there ase sometimes 

 found the grey fruit-bodies of a Diplodia or of a Chaeto- 

 diplodia; if the branches are kept in a room, whether or 

 not under a glass bell-jar, such fructifications are always 

 observed after a few days. 



There also occurs in the cacao-fruits a disease, which 

 must be considered hère, for, as will be seen later, its 

 cause is the same as that of the die-back disease of the 

 trees. On eut pods, and pcrhaps also on fruits which 

 still hang on the tree — but this point is still doubtful — 

 a brown spot sometimes arises, which very much re- 



