CITEUS DISEASES. 7] 



fnngi becomes soft and crumbly, so that eventually cavities are pro- 

 duced, which increase slowly in size as the rot works into the tree. 

 Decay of this sort should be, and in most cases is, readily apparent 

 to the grower, so that steps may be taken to check its spread, or 

 eliminate it entirely. 



However, there is another type, one that is more prevalent and 

 much more dangerous, because not so easily located. This is a rot 

 of the heart or center of the trunk or branch. An entrance is gained 

 through a wound and from this point the rot spreads slowly up and 

 down the trunk, and eventually into the larger limbs. Once an 

 entrance is effected, decay progresses slowly (often over a period 

 of many years) though none the less certainly, until the tree is 

 destroyed. Lateral progress is not as rapid as that along the main 

 axis of the tree. Rot of this type is generally dark colored and not 

 less firm than normal wood until an advanced stage, when it becomes 

 soft and friable. Rotted wood is, however, always much weaker 

 than normal or healthy wood, which permits breakage by heavy 

 M'inds, and other destructive agencies. 



In the former type (sap rot or rot of the outer wood layers and 

 bark) there is. of course, direct harm to the tree in that the water- 

 and food-conducting tissues are destroyed, and the normal life pro- 

 cesses of the tree interfered with, to an extent depending upon the 

 size of the diseased areas. This would vary from a slight weakening 

 to death, where the tree was girdled. In the case of heart rot, while 

 possibly no direct injury results since heart wood is composed of 

 dead tissues and takes no part in the transport of food or raw mate- 

 rial for the use of the tree, the way is paved, through its slow but 

 persistent action, for a premature death of the tree by helping to 

 bring about a general weakening, in which condition other harmful 

 agencies can complete the work of destruction. 



Wood I'ot of all kinds is produced not by the action of the weather 

 or by exposure to moisture or the air (although these are important 

 contributing factors), but l)y the work of certain fungi. Several 

 at least are concerned, it being possil/le to distinguish the work of 

 one from that of another. Certain ones rot the sap wood only, others 

 the heart ; some produce a light-colored rot, and others a dark 

 colored type. However, since the treatment or prevention of all 

 types is practically the same, there is no need of going into further 

 details on this point. 



Without exception the fungi under consideration gain entrance 

 only when some other agency has made an opening — or that is to 



