232 
Journal of Agricultural Research 
Vol. XXIV, No 3 
bErk is at first soft, later dries out into long shreds, and usually con¬ 
tains flat sclerotia within it. 
(21) Inoculations with pure cultures have shown that this fungus 
may also kill the bark rapidly and bring about the results just men¬ 
tioned on healthy lemon tree trunks. 
(22) Inoculation experiments with a large number of other organisms 
showed that some of them were capable of inducing gum formation, but 
this effect was usually slight as compared to that of Pythiacystis, 
Botrytis, and Sclerotinia. Those which produced some gum exudation 
in cuts were Penicillium roseum, Fusarium sp., Diplodia sp., Coryneum 
herynkii, Coprinus atramintarius, Alternaria sp., and Hypholoma sp. 
The effect in killing of bark was insignificant, and no definite diseases 
resulted.^ Several other organisms produced no effect whatsoever either 
in inducing gum exudation or killing tissue. 
(23) In Parts I and II of this paper the relation of certain fungi to 
definite types of diseases in which gum is a conspicuous feature has been 
discussed. 
(24) Gum in Citrus is similar to gum arabic and cherry gum and 
appears to originate mainly in the xylem tissue by hydrolysis of the 
cellulose walls. 
25) Attempts to induce gum formation in lemon trees by various 
mechanical injuries, by obstructions placed in the conducting tissue, 
and by pressure on the bark, failed when the tissues experimented upon 
were free from parasitic organisms or unusual chemical stimuli. 
^ (26) Injuries from certain insects have been observed to result in 
slight gum formation, which is probably due to secretions by the insects 
or to contaminating organisms. 
(27) Experiments and observations indicate that burning and freez¬ 
ing are not important factors in inducing gum formation in Citrus but 
merely serve to open up the way for parasitic and wood-rotting fungi, 
which afterwards induce gumming. 
. (28) Partial desiccation appears to be merely a factor in the accelera¬ 
tion of the process of gum formation in Citrus and not a necessary con¬ 
dition to its initation. 
(29) Certain chemical substances are capable of inducing gum for¬ 
mation when injected into Citrus bark. It has not been possible, how¬ 
ever, to reproduce all the typical symptoms of any of the gum diseases 
by chemical injections. The invasion of certain parasitic organisms 
appears to be the chief factor in initating gum formation under natural 
conditions. These organisms may bring about, as do certain chemical 
substances, gum formation over considerable areas of bark surrounding 
the portions killed by either the organism or the chemical substance. 
(30) Comparative experiments with boiled and unboiled filtrates 
from diseased and healthy tissue show that the diseased bark contains 
a substance capable of passing through a fine clay filter and of inducing 
gum formation when unboiled. When boiled, however, this capacity 
to stimulate gum is destroyed. This indicates the presence of a heat- 
sensitive enzym. 
LITERATURE CITED 
(1) Anonymous. 
1882. ORANGE tree cultivation. In Trop. Agr., v. 2, p. 505-506. 
(2) Aderhold, Rudolf, and Ruhland, W. 
1907. DER bakteriEnbrand der kirschbaume. In Arb. K. Biol. Anst. Land, 
u. Eorstw., Bd. 5, p. 293-340, 12 fig., pi. 9. Literatnrverzeichnis, p. 
339-340. 
