47 



no water sprouts develop from the interior of the tree top or 

 from the trunk. In Florida trees are not usually attacked 

 until they are quite old and have been bearing fruit for a 

 number of years. In other regions, however, young trees are 

 said to contract the disease. 



Psorosis. a disease (11) known in Florida as "tears" or 

 "gum disease" is often confounded with the foot-rot, but is 

 unquestionably quite distinct. In appearance, it is similar to 

 foot-rot, but with it the diseased spots occur on the limbs and 

 occasi mally on the trunk, but never on the roots so far as 

 known. Psorosis does not kill the bark entirely, but extends 

 only to the middle layer, the inner bark and carbium layer 

 remaining healthy. 



Varieties of Tiiees Attacked. — Probably all species of 

 citrus trees may contract mal-di-gomma, but some are very 

 much more subject to it than others. Sweet seedling orange 

 trees (Citrus Aurantium) are particularly susceptible, and it is 

 in old groves of these that the most damage is done. Sweet 

 orange used as a stock for budding is also liable to the disease. 

 This malady is very destructive to the lemon (C. limonum), 

 occurring quite commonly on all varieties. Grape fruit (0. 

 decumana) is frequently affected, but is much more resi stent 

 to attacks than the sweet orange or lemon. Indeed, it is 

 seldom that this fruit is seriously damaged. Tangerine and 

 mandarin oranges (C. nobilis) are occasionally affected, but 

 the damage is not usually very great. The sour orange (0. 

 bigaradia) is apparently almost wholly free from mal-di-gomma. 

 The writers carried on a careful search for the disease on this 

 species, but succeeded in finding only two unquestionable 

 cases. The sour orange used a stock for budding, remains 

 free from attacks, and in Florida its use for this purpose is 

 almost a sure preventive of the disease. It is probable that 

 the disease occurs on the lime (C. lirnetta) and citron (C. 

 medica) also, but no cases have as yet been observed in Florida. 



Cause. — Mal-di-gomma has been studied extensively by 

 many investigators, but as yet the cause of the disease is not 

 surely known. It is thought by many to result from the 

 attacks of some parasitic organism, and Professor Briosi 

 (Briosi, loc. cit., 495) describes and names a fungus (Fusis- 

 porium limoni) which he finds always accompan) ing this 

 disease. He is inclined to consider the fungus the cause of the 

 trouble, but is in doubt as to whether it is the primary cause. 

 He says, however: "I do not believe there can be any doubt 



(11) From the Greek, meaning an ulcer. 



