29 



walory, somewhat "[iimmy substance under the bark which is without 

 perce])til)le odor. The cambium hirer or inner ])ark is not destroyed, 

 and the tree is able to recuperate. Tlie disease has in no case been 

 observed to extend below the soil or on the main roots. It has been 

 observed on sweet oran^re, lemon, grape fruit, and sour orange, 

 although not often on the latter. This disease is often described as 

 being of a bacterial origin and contagious. \Miile it is no doubt 

 safest to treat it as such, the indications are that the causes are physi- 

 ological. It has been found on all classes of soil, but it is much more 

 prevalent on the heavier soils than on those which consist mainly of 

 sand. It is also frequently found in the rainy season, while in the 

 dry season the trees have been known to overcome it entirely. It 

 has been observed frequently on trees less than two years old and not 

 so often on trees over three. It appears that an oversupply of mois- 

 ture is the usual cause, and probably an oversupply of plant food 

 tends to aggravate the disease. 



Gum disease has often been confounded with the effect of an 

 attack by ants, because ants usually follow and greatly aggravate 

 the case. Several remedies have been tried, among which are tar 

 and girdle ]:)aint, the latter made according to directions given in Circu- 

 lar No. 4 of this station. Both of these are good if the diseased bark 

 is first cut away and the material painted over the open sore only. 

 Cases have been observed where these mixtures were applied without 

 removing the diseased bark, and the disease continued under the bark 

 without interruption. Also where the mixtures were applied all 

 around the trunk the effect would be the same as a tight bandage, 

 which could be detected twelve to eighteen months after the applica- 

 tion was made. A thick soap mixture containing about five parts 

 of crude carbolic acid is now being used successfidly; It covers the 

 sores and acts as an antiseptic as well as a repellant for ants. 



Leaf spot caused by a fungus (Colletotrichumglceosiwrioides) is found 

 on the grape fruit in some groves, and these trees are also occasionally 

 attacked by scab. Both of these can be checked with Bordeaux 

 mixture or ammoniacal copper carbonate, but these mixtures should 

 not be applied unless necessary, because they also kill the fimgus 

 parasites of the scale. 



THE PRESENT OUTLOOK. 



The question of growing an orange tree in Porto Rico so as to 

 obtain the maximum result at minimum expense can be expressed 

 with the one word "experience." . Groves three to four years old, 

 which have been intelligently treated, are looking very promising 

 and some are bearing considerable fruit of good qiuility. As to the 

 most desirable varieties it is impossible to state definitely at the 

 present time. Grape fi'uit is extensively planted and is very vigor- 



