80 
FLORIDA STATE HORTICULTURAL SOCIETY. 
r 
Miami. He proved by experimental meth¬ 
ods that by spraying the spores of a cer¬ 
tain fungus upon the young orange and 
lemon trees in the greenhouse he could 
cause the disease known as Withertip. It 
was demonstrated in this way that the 
disease was caused directly by the fungus 
known as Colletotrichum gloeosporioides. 
It was further shown that other effects 
were due to the same cause, such as blos¬ 
som-blight, leaf-spot, tear-staining of 
fruit, lemon spot, and other troubles. Dr. 
Ernst A. Bessey, in carrying this work 
further, demonstrated that the same fun¬ 
gus which causes withertip of orange *n 
its various manifestations, also causes 
blossom-blight, leaf-spot and fruit-rot of 
mangoes and avocadoes, and leaf-spot 
and fruit-rots of various other plants. 
Withertip has so many different ap¬ 
pearances and symptoms according to 
what part of the tree is affected and at 
what stage of development it is found, 
that it is almost impossible to give a de¬ 
scription of it by which it can be identi¬ 
fied at all times. The fungus causing 
withertip appears to be an ever-present 
one, and the disease breaks out in its de¬ 
structive form as the result either of the 
action of virulent strains of the fungus, 
or from unfavorable conditions that ren¬ 
der the tree less resistant to the growth 
of the fungus into its tissues, or from both 
causes. Withertip often accompanies or 
follows other troubles. It is almost in¬ 
variably found as a secondary agent in 
trees suffering from scaly bark. It ap¬ 
pears that the scaly bark disease was pres¬ 
ent for years, and only developed in its 
present destructive form after the ad¬ 
vent of the Withertip in the State. Prof. 
B. F. Floyd has observed that it nearly 
always follows the yellow spotting of 
citrus leaves. The resistance which a 
strong healthy tree presents to this fungus 
is probably lessened materially through 
the influence of yellow spotting and the 
fungus can then enter the weakened tis¬ 
sue. There are certain effects of fertil¬ 
izers that appear to increase the liability 
to this disease. Prof. Floyd in his experi¬ 
ments with the physiological effects of 
certain kinds and amounts of fertilizers 
on young trees, found that by increasing 
the amount of nitrate of soda till a poi¬ 
soning effect on the wood tissue resulted, 
a condition was produced suitable to the 
rapid development of Withertip. In 
cases where amounts of phosphoric acid 
or potash were used sufficient to poison 
trees to the same degree, the Withertip 
was not observed to develop to the same 
extent. 
What usually puzzles the grower is 
that often there are individual trees, and 
even individual limbs of the same tree, 
that are severely attacked; while other 
trees of the grove and other limbs of the 
diseased tree remain uninjured. This 
difference in the action of the fungus to¬ 
ward different limbs of the same tree is 
probably due to a difference in the vitality 
of the individual limbs. Any cause ren¬ 
dering a branch somewhat weak, such as 
a previous heavy load of fruit, or the ad¬ 
verse conditions mentioned above, would 
most probably render that branch sus¬ 
ceptible to an attack of the fungus. The 
same would doubtless be true in regard 
to the susceptibility or immunity to the 
disease of the different trees in a grove. 
Cases occur, however, that seem to be 
accounted for only by considering trees 
as individuals, each slightly different 
