70 JOURNAL or AGRICULTURE OF P. R. 



greater need for care, since a virulently parasitic fungus is present, 

 and in great quantity. All prunings and other diseased .material 

 cut out should be destroyed, and all sanitary precautions observed. 



Gumming will often occur where no specific diseas(? is present, 

 and is often due to mechanical injury, insect work, or other similar 

 causes. Citrus trees form gum freely at any wound, apparently as 

 a first step to healing, the gum being slightly antiseptic. In all such 

 instances the wound should be thoroughly cleaned out and treated 

 with a protective dressing, the cause l)eing removed or corrected if 

 present. 



WOOD ROT.^ 



Some idea of the importance of this trouble may be gained when 

 it is stated that there is not a grove on the Island which will not 

 show some cases at least, and that there are groves in which prac- 

 tically every tree is infected. Instances have been seen where the 

 disease had progressed so far that many trees were dead and the 

 bijlance of a given block or grove in advanced stages of decay. Con- 

 sequently there is no hesitancy in saying that this disease will play 

 a most important part in grove decadence in the not very distant 

 future. In fact, it is doing that at this very time, but the effects 

 when considered at all have been referred to other causes, and it 

 has been but seldom that any steps have been taken to prevent or 

 control the trouble. 



Characteristics and causes. 



Wood rot is here used as a general term to cover a rot or decay 

 of the wood of the trunk and larger branches, caused by a number 

 of different fungi; for while several different types of rot may be 

 distinguished, it is sufficient from the practical view point of control 

 or prevention to consider them as one. 



This disease has been well characterized as insidious. A tree may 

 be in an advanced stage of decay without there being any surface 

 evidences visible, unless careful search is made. The damage often 

 becomes apparent only after a storm or other agency has brol\en 

 a limb or split the trunk, exposing the rotted interior. 



Several quite distinct types of decay occur, in some instances of 



■ the sap wood or outer wood layer only. In this case the bark will 



as a general rule also be involved, resulting in large trunk or branch 



cankers. In this type the wood through the action of the attacking 



^A partial reprint of Circular 10, Insular Kxperiment Statimi. 



