48 



that its presence accelerates the disorganisation of the tissues 

 and aids in extending the disease." 



The manner in which the disease spreads, appearing at 

 different dates first in one country and then in another, and 

 extending gradually from grove to grove, strongly indicates 

 that it is contagious, being caused or at least greatly aggra- 

 vated by some parasitic organism. Some investigators also 

 think that the disease is due to physiological derangements, 

 for instance, imperfect aeration of the roots. The most 

 effective treatment known is based largely on this supposition. 



Observation has shown that the disease is most common 

 where any of the following conditions exists : Improper drain- 

 age ; planting the trees so close together that the ground is 

 continually shaded and kept moist ; continuous use of organic 

 fertilisers ; excessive cultivation ; continuous excessive irriga- 

 tion, which keeps the soil water soaked ; and deep planting. 



Trees badly effected with the disease frequently recover if 

 transplanted to some other location, on apparently similar soil, 

 and given plenty of room. A remarkable instance of this was 

 seen by the writers in a case where 40 acres were planted out 

 some five years ago with large trees affected with foot-rot. 

 After three years every tree of the several thousand transplanted 

 to this grove seemed to have fully recovered. 



Treatment. — Very many attempts have been made, both in 

 Europe and in the United States, to find remedies for this 

 malady. One of the most important discoveries is that it can 

 be prevented by using immune or resistant stocks. It was 

 early noticed that the sour orange and trees of sour orange 

 stocks were almost absolutely exempt from the malady. By 

 using this stock in setting out young groves the disease can be 

 effectually prevented. On high, dry, soils, not suited to the 

 sour orange, grape fruit stock can be used, as it is also quite 

 resistant. 



Many curative treatments prove more or less beneficial, and 

 this has led to conflicting claims as to which is the best. In 

 many cases it has been found sufficient to simply dig away the 

 earth and expose the roots. This probably explains why so 

 many different applications made to the roots seem to benefit 

 the tree The very ac of opening the soil and exposing the 

 roots to the air of itself tends to effect a cure As the disease 

 is probably caused by a pirasite, it is important that no 

 wo.inds be made on healthy roots in removing the soil. It is 

 desirable to cut away all infected bark and wash the scars 

 with some anti-septic solution, such as sulphurous acid, carbolic 

 acid, or sulphur wash, Where trees are closely planted it is 



