FUNGOUS AND PHYSIOLOGICAL DISEASES. 479 



black screen of fungal threads prevents the light from 

 reaching the leaves. Their natural functions are inter- 

 fered with and the tendency is to keep the tree in an un- 

 healthy condition. Often the yield of bearing trees is 

 greatly lessened as a direct consequence. 



Bearing on the effects of sooty-mold and white-fly 

 on citrus trees, the following remarks by H. A. Gossard, 

 in Bulletin 67, Florida Experiment Station, are of in- 

 terest : 



"The following table shows the results of a chemi- 

 cal analysis made at my request by Professors Miller 

 and Blair, of three lots of fruit picked the same day from 

 adjoining Dancy tangierine groves, both of which were 

 infested with white-fly and had been given practically 

 the same treatment as regards cultivation and fertiliz- 

 ing. Fifteen or twenty oranges were selected for each 

 of the three lots, representing as accurately as possible 

 the average condition as to size and maturity on each 

 of the three trees from which they were taken. 



"Sample No. 1 was from a tree that had been in- 

 fested for several years and had been left to take care 

 of itself. 



"Sample No. 2 was from a tree about forty feet from 

 No. 1 and was regularly and properly sprayed three or 

 four times each year, but stood in the row adjoining the 

 unsprayed grove, and the insects could not be prevented 

 from developing upon it in numbers sufficient to cause 

 more or less mold. 



"Sample No. 3 was from a tree eighty feet from No. 1 

 and was properly sprayed as was No. 2, but with better 

 results. A few larvae were present on the leaves, but, 

 practically, white-fly could be considered wholly absent. 



