THIRTY-FOURTH FRUIT-GROWERS^ CON\TENTION. 



83 



process in the tree, and occurs in the trees mentioned, often very 

 profusely, from a great variety of causes. It may be due to mechanical 

 injury, to the effects of fungi, as seen for instance in the peach blight, 

 or simply to physiological derangements in the tree. The gumming 

 disease may be likened to a form of indigestion, or in some degree to the 

 abnormal activity of the mucous membranes seen in a person suffering 

 from a cold. 



In taking up now in detail some of the more prominent diseases to 

 which citrus trees are subject in California, we would not be under- 

 stood as maintaining that they may be all easily explained as due to 

 easily seen effects or evident causes, or that they may be easily remedied 

 by simple rules of irrigation, cultiA^ation, or fertilization. We mean 

 rather to simply express a belief that these troubles are of the nature 

 described, even though complicated and obscure and difficult of treat- 

 ment in many cases. 



Under the general term of gum disease are included several troubles 

 of a more or less distinct nature. Of these may be mentioned partic- 

 ularly the gum disease of the lemon, the scaly bark of the orange, and 

 the true gummosis. or ]Mal di Goma of Europe and Florida. The last 

 mentioned disease is quite distinct from the most common forms of 

 gum disease which occur in California. It is characteristically, a disease 

 of the root rather than of the trunk, and may be described as a root rot, 

 more than a simple gumming. We have seen this trouble only in a very 

 few instances in California. It affects the tree mostly from the surface 

 of the ground downward, and shows itself, as a softening and decay 

 of the bark, finally affecting the whole root. So far as seen here, it 

 appears to be due to an excessive amount of moisture about the trunk, 

 particularly when accompanied by banking of the earth closely around 

 the tree above the normal height. 



The gum disease of the lemon manifests itself as a breaking out of 

 gum on the trunk, usually between the point of budding and the main 

 forks of the tree. This disease has been much discussed of late in the 

 horticultural press and elsewhere, and the conditions which produce it 

 are quite generally understood. It is without question entirely physio- 

 logical, and not brought about or concerned in any manner with any 

 fungi, bacteria, or other parasites. It occurs almost ahvays in heavy 

 ground, in places where moisture is too abundant, and particularly 

 where the soil has become compact about the trunk above the point 

 of budding. Instances are practically unknown of lemon trees being 

 affected, save under conditions of this sort. The lemon gum disease may 

 be avoided in no other manner than by avoiding these conditions which 

 bring it about, or when once started may be remedied in no other 

 manner than by improving said conditions. This may be done very 

 largely by cultural means, consisting -of loosening the soil thoroughly 

 about the trees, uncovering roots which are too deeply buried, avoiding 

 saturation of the soil close about the tree, and, if feasible, replacing the 

 iiea^T soil with sand or gravel in a circle about the tree. If planting 

 in soil which is manifestly liable to the disease, two things are strongly 

 advisable. First, the use of the bitter orange or so-called- Florida sour 

 s^ock for a root : the second, the practice of high budding, working the 

 tree about fifteen inches from the ground. In the case of trees already 

 affected, it is often advisable to remove the bark which has become 



