14 



place near or beneath the ground, the ibliage is affected, and becomes 

 yellow and sickly from the insufficient supply of nourishment from 



the roots. 



The exudation of gum at the collar, the decay of the bark there 

 in patches, and the consequent disagreeable odour, the unhealthy 

 appearance of the foliage, and the death of the small shoots, are all 

 symptoms of this disease. 



Generally the first visible intimation of the disease is the fruit 

 setting abnormally thick, and the foliage turning a sickly yellow 

 colour. This fruit-setting is an evident effort of the tree to provide 

 successors before it finally perishes. 



Effects. — When trees are attacked, they may produce an extra 

 large crop of fruit the first season, but this is usually the expiring 

 effort, and little or none is produced afterwards. In a few months 

 the "ring-barking' 1 of the stem may be almost completed, and. as 

 the disease spreads from tree to tree, in the course of a few years 

 entire orchards may be devastated. The progress of the disease will 

 be rapid or slow according as the conditions favour it or otherwise. 



The healthy root action is interfered with, and there is a defi- 

 ciency of nourishment ; the foliage is affected and is unable to 

 assimilate properly : the girding of the stem prevents that free com- 

 munication between root and leaf which is essential to plant growth : 

 and finally, with the destruction of the cambium layer — the centre of 

 vital activity— the tree is doomed. 



Conditions favouring Disease. — The conditions which favour the 

 disease are often confounded with the cause ; but Ave must distinguish 

 between them. They are what may be called predisposing causes — 

 conditions which affect the plant injuriously and render it liable to 

 the attack of the fungus parasite. They may be guilty of aiding and 

 abetting and preparing the way for the fungus, but of themselves do 

 not induce the special disease known as "collar rot." As far as 

 known, it is necessary that this particular fungus invaded the 

 weakened tissue in order to produce; the characteristic symptoms 

 which we speak of as the disease : and whatever is antagonistic to 

 these conditions, or destructive of this fungus, will tend in the direc- 

 tion of preventing or remedying the disease. Unsuitable soil is said 

 by some to produce the disease, because it always occurs towards the 

 base of the stem, near to or beneath the surface of the soil: but 

 transplanting the trees to similar soil may lead to their recovery. 

 Sudden changes in the temperature of the soil surrounding the stem 

 are also supposed to induce it. the sudden and extreme variations 

 affecting the regular flow of the sap and producing contraction and 

 expansion of the bark. 



The want of proper drainage is likewise a contribut ing condition, 

 because it will prevent the perfect aeration of the roots, and the water 

 may be allowed to lodge around the stems. 



Close and deep planting, producing an excess of shade and a 

 deficiency of feeding roots : rxecssire Irrigation, keeping the soil 

 soaked with water : excessive cultivation, which may tend to injure and 

 disturb the roots : and the continuous use <;/' organic fertilizers, are 

 all said to encourage the disease. 



