62 

 CHAPTER XVI. 



DISEASES TO WHICH THE ORANGE TREE AND FRUIT ARE LIABLE, AND 

 THIER REMEDIES. 



Few fruit trees are less liable to disease than the orange, but the 

 fruit and trees are so valuable that no enemy should be allowed to 

 attack them unopposed. Perhaps the most formidable disease which 

 has yet made its appearance is the "die-back." Two causes producing 

 this disease have already been noticed in a preceding chapter. The 

 name "die-back" is a general term, used for want of a better and 

 more specific name or names, for at least two diseases arising from 

 three and perhaps four different causes. But as it is descriptive of the 

 symptoms of one or more diseases arising from several different causes, 

 its meaning is readily comprehended. The symptom is the dying 

 back of the new wood to the old. It is sometimes confined to a few 

 branches of the tree. When this is the case the inference is that it is 

 caused solely from the sting of an insect. If, however, the symptom is 

 general to the young branches and they come forth, feeble and yellow 

 with no marks of stings, the cause may originate near the roots. 



Deep planting will produce such symptoms. Trees do not depend 

 solely upon their leaves for the supply of carbonic acid. The roots 

 gather a very considerable part of this gas, so essential to plant life, 

 not in a pure state, as is done by the leaf, but in chemical combination 

 with other elements. This is the case especially with trees which have 

 very yellow roots. Such trees send their roots either into a very 

 porous soil easily penetrated by the air, or else send them near the sur- 

 face, where they find a greater abundance of air, which decomposes 

 manure and is essential to the formation of carbonic acid. Such is the 

 case with the orange tree and roots. If the tree is planted too deep or 

 the crust on the top of the soil has become very compact, these roots, 

 dependent upon air for health and ability to perform their functions, 

 are virtually smothered. They make an effort to grow, but as often as 

 they form rootlets and roothairs, these die and convey no nutriment 

 for the formation of the woody structure of young shoots, so the new 

 and tender cells, which are but the frame work of the plant, perish for 

 want of support. And hence the light cellular structure in the forms 



