52 



able odor. In summer or winter when the effusion of gum decreases or 

 stops, the greater part of the bark around the point of infection dies and 

 becomes detached from the wood. When dry it springs away from the 

 wood and becomes hard and brittle. The surface of the wood under- 

 neath the bark is also affected to some little distance in all directions 

 from the point of infection. The most vital part of the trunk, the cam- 

 bium layer, which lies between the bark and the wood, is destroyed, 

 and each year this destruction extends until it has made the round of 

 the trunk girdling the tree completely, thus cutting off alLcornmunica- 

 tion of the vital fluids between the roots and the top, which is-certaiu 

 death to the tree. 



When the disease attacks the roots the death of the tree follows more 

 rapidly — sometimes in less than a year. The sudden changing of the 

 leaves to a sickly yellow color is the first visible symptom of the disease 

 when the roots are attacked. It must be kept in mind, however, that 

 the leaf-yellowing may be due to other causes. Such is the diagnosis 

 of the disease as it appears in Europe, and according to the reports of 

 correspondents it is evidently the same as that which prevails in 

 Florida. l 



III. Conclusions as to the Cause of Gum Disease. 



So far the cause of the disease is not certainly known, but this does 

 not appear to be due to a lack of interest; for many scientists have in- 

 vestigated the matter and large rewards have been offered to stimulate 

 these researches. 2 According to Sorauer 3 the gum when carried to 

 healthy parts of the tree by the action of rain or other agents induces 

 disease; but all attempts made here to convey the malady to healthy 

 orange trees by inoculations have failed. A microscopic examination 

 of the diseased tissues and gum reveals the presence of a vast number 

 of bacteria and filamentous threads of some fungus or fungi, but what 

 connection these may have with the disease has not yet been ascertained. 

 It appears from BriosrV researches, that the disease in Italy is always 

 accompanied by a fungus to which has been given the name Fusarium 



' Dr. Curtis, in the Bulletin already referred to, describes the disease as follows: 

 The prominent symptoms are exudation of a gummy or sappy fluid from near the base 

 of the trunk, and decay of the bark in that region and of the roots below. . The flow 

 of gum and attendant decay extend upwards and in a lateral direction until the tree 

 is girdled, also penetrating successive layers of wood. In some cases gum exudes 

 from cracks in various parts of the trunk, or even on the branches, and in others the 

 decay progresses without emission of gum. Attendant or premonitory symptoms are 

 excessive and rather late blooming, the flowers being small and mostly unfruitful, 

 and arrested and unnatural development of the foliage, which becomes yellow and 

 drops. The disease manifests itself in the top on the same side aa at the base, and 

 makes like progress above and below. 



-The Italian minister of agriculture has offered a reward of 25,000 lire ($5,000) 

 for an effectual remedy. 



3 Pflanzenkrankheiten, 18S6 ; page 679. 



4 I1 male di gomma uegli Agrumi. 



