THE CITRUS WHITE FLY: INJURY. 19 
with an average of about 11 live larvae and pupa cases 1 per leaf, were 
slightly blackened. In general, heavy coats of sooty mold on leaves 
are common in Florida by the 1st of June in groves heavily infested 
by the citrus white fly. 
Effect of sooty mold on leaf functions. — Dr. Webber has discussed 
the effect of sooty mold on leaf functions in the report already referred 
to, and as there is nothing to add at this time, the following paragraph 
(pp. 10-11) is quoted: 
When it is remembered that various investigations have shown that the process of 
phytosyntax 2 is almost entirely checked in a plant placed in the back part of a living 
room, opposite a window, where the light is fairly bright, but diffused, it can readily 
be judged that the effect of the dark, compact mycelial membrane of the sooty mold 
covering the leaves would be to almost wholly check the process of phytosyntax in the 
orange tree. Quite bright or direct sunlight is necessary for the best results. The 
injurious effects of sooty mold on the phytosyntax was clearly demonstrated by Busgen. 
He removed the fungus membrane from a small portion of a leaf and exposed the leaf 
to the sun. In the evening, after a sunny day, the leaf was plucked and the chlorophyll 
extracted with alcohol. After this leaf was treated with iodine, the parts from which 
the membrane had been removed in every case stained a dense blue, indicating the 
formation of an abundance of starch, while the surrounding portions of the leaf, which 
were protected from the sun by the fungus membrane, remained entirely uncolored, 
showing that no starch was formed. The stoma ta, or breathing pores, are also to some 
extent closed by the sooty mold, and in this way the passage of gas is more or less 
hindered. In the orange leaf, however, the stoma ta are confined to the lower surface, 
where generally there is but little sooty mold. In plants where the stoma ta are on the 
upper surface of the leaf also, the damage resulting from the obstruction of the passage 
of gases would probably be considerably greater. 
Extent of Injury. 
In the following discussion the statements concerning injury and 
the estimates of the extent of this injury by the citrus white fly refer 
to groves in which the fly has become well established and in which 
no remedial measures have been practiced. 
INJURY TO FRUIT. 
Unless otherwise stated, oranges and tangerines are referred to. 
These constitute more than 88 per cent of the citrus fruit crop of 
Florida. The total injury to grapefruit by the citrus white fly is 
rarely over 15 per cent and is frequently inappreciable. 
Ripening retarded. — Ripening of fruit on heavily infested citrus trees 
is greatly retarded, and in case of the formation of a very heavy coat- 
ing of sooty mold on the upper half of the orange the rind underneath 
it may remain green indefinitely while the lower half of the fruit is 
1 Some of the first generation had matured, but are properly included with the 
insects responsible for the sooty mold present. 
2 ' ' Phytosyntax ' ' refers to the process of the formation of complex carbon compounds 
out of simple ones under the influence of light; ' 'photosynthesis" is a more common 
term for this process of assimilation. 
