DISEASES OF CITRUS TREES ] 57 



a microbe, Bacterium gummis, Comes. When attacking 

 the trunk or branches the disease is usually accompanied 

 by an exudation of gum The disease usually has a latent 

 beginning. The bark on a certain spot in the trunk or 

 branches becomes darker and shining, as if covered with 

 a thin layer of varnish. In a vveek or two a small crack- 

 is formed in the bark, and a semi-liquid gum of a reddish 

 brown hue oozes out in variable quantity, and is more 

 abundant after irrigation. In a few days more the gum 

 becomes more liquid, clearer, and of a lighter colour, 

 sometimes perfectly colourless. The dark shining spot 

 increases in size till at last a large part of the perimeter 

 of the trunk is infected. The bark around the fissure 

 dies soon after the gum begins to ooze, and is easily 

 separated from the wood, which is found to be dead all 

 around the fissure. New points of infection develop above 

 and below the first, and when the tree is approaching its 

 end, the gum again oozes out in a semi-solid state, torpid 

 and brown. By this time several of the large branches 

 will have died and the tree reduced to little more than a 

 stump. 



When the disease appears on a large branch some- 

 times no gum is formed, but the bark dies, cracks, arid 

 separates, leaving a long patch of dead ashy coloured 

 wood, usually upon the upper surface of the branch. 

 When the disease attacks the roots or the base of the 

 trunk gum is rarely formed, but ashy spots are developed 

 on the bark of the roots or trunk, and underneath them 

 the wood is dead, ashy-grey, and often in a half-rotten 

 state. The dead roots are commonly covered all over 

 by the silvery root-like mycelium of a saprophytic 

 mushroom, of Agaricus Citri or of Armillaria mellea. 

 The growth of these mushrooms near the base of the 

 trunk of a Citrus tree should be looked upon with 

 suspicion, it is a hint that some roots may have been 

 destroyed by gummosis or by root-rot. 



Gummosis generally takes from three to eight years 



