DISEASES OF CULTIVATED PLANTS 515 



substance the fungus lives. The black covering is composed of its 

 vegetative threads. A number of different kinds of reproductive 

 bodies are produced, and, through the agency of the wind, are car- 

 ried about from tree to tree. Wherever suitable food material is 

 found, there the fungus develops. 



It is when it follows the attacks of the white-fly or mealy-wing. 

 Aleyrodes eitri, that the fungus most frequently causes damage in 

 the orange groves. This insect spends a great portion of its life on 

 the under side of the leaves. The honey-dew exuded by it, falls 

 upon the upper sides of the leaves beneath, and upon the twigs and 

 fruit. Whole groves are to be seen in the State to-day, the trees in 

 which have their leaves completely covered by Meliola. The trees 

 from a distance appear as though they had been coated with a 

 liberal application of stove-black. 



Sunlight is necessary to the leaves of a tree in order that 

 they may carry out their work in the plant's economy. The black 

 screen of fungal threads prevents the light from reaching the leaves. 

 Their natural functions are interfered with and the tendency is to 

 keep the tree in an unhealthy condition. Often the yield of bearing 

 trees is greatly lessened as a direct consequence. The remedies con- 

 sist of such treatments as will destroy the white-fly; that accom- 

 plished, the sooty mold no longer having food in which to develop, 

 will disappear. (Fla. E. S. B. 63.) 



Blight. Blight is the most dreaded of all the citrus diseases in 

 Florida. The trees appear as though suffering from drought, or in a 

 manner similar to ones recently set out. The leaves wilt, and droop 

 and finally drop off. In some cases the disease works very rapidly, 

 in others its progress is decidedly slow. It often manifests itself on 

 a single branch and from that gradually spreads over the whole tree. 

 Trees affected in this way live for a considerable length of time. 

 On the other hand, it may act very rapidly; for instance, on one 

 tree the disease commenced in a definite area on one side of the top 

 and quickly spread both ways round the head, meeting on the oppo- 

 site side. The tree in this case quickly succumbed. Usually, how- 

 ever, new shoots are put out, which grow well for a time, but later 

 yield to the disease. 



Up to this time the cause of blight remains unknown. It ap- 

 pears among old bearing trees, which are well cared for in every 

 way, and which up to the time of attack are apparently in perfect 

 health ; therefore, it can not be assigned to any external cause. The 

 key to the successful treatment of any plant disorder is to know the 

 cause and nature of the ailment. This has not yet been found. 

 Furthermore, my observations have gone to confirm those of others, 

 that the disease is likely to spread from one tree to another. Treas 

 once affected rarely, if ever, survive, and the best treatment is to dig 

 out and burn the affected ones and place others in their stead. This 

 is the most economical plan as well, because affected trees never 

 repay the time and trouble taken with them. (Fla, E. S. B. 63.) 



