Journal of Agricultural Research 
Vol. XXIV, No. 3 
224 
kept clean and reasonably free from contamination with microorganisms 
or unusual chemical substances. 
A number of experiments were carried out to test (a) the influence ©f 
various kinds of grounds, (b) the influence of obstructions in the sap 
current by insertion of substances such as glass or wooden plugs, and 
finally (c) the influence of continued pressure upon the bark. Most of 
these experiments were performed with and without contamination with 
spores from pure cultures of Botrytis cinerea and are shown in Table XVII. 
• Tabi«E -■-‘Experiments with injuries with and without contamination, started in 
July, 1^121 on sound trunks of i8-year-old lemon trees at Santa Paula 
Treatmeat of tree. 
slice of outer bark cut off and microscopic slide 
I piitty-. .. • ... . ....... 
olmace’di bark iightly scraped and covered as above.......... 
‘Bdrk^di injuted but covered as above. . .... 
' liotig slits m^e through bark and covered with grafting wax_ 
. ^e^ of barkabout 8 by 4 cm. cut away and covered with cold 
,liquid grafting w^.......... 
nark dn truhk injured with heel of heavy boot, as if climbing tree. 
Bark mjiired by throwing wire coal basket against trunk......... 
Bark injured by blow from blacksmith’s hammer and covered 
__V ... • ... .. 
f.^ug^^r holes.i.3 to 2 cm. deep and i to 1.5 cm. in diameter filled 
With jgl^ tubes and sealed in with wax. 
exerted a^iUst wooden blocks, on opposite sides of tree, 
;j 1 by.^^nieaiis of fscrews in an iron collar.... 
Number of experiments. 
Not inocu¬ 
lated. 
Inoculated. 
. ; ,^ne of injuries shown in Table XVII, kept uninoculated, was 
exudation or development of the disease. All such 
iujuries he^ed in lAe usual way. With all the experiments in which 
spores qJ were used as a contamination, however, except 
iWher^e the.hark was not injured and one of those with glass tube used ^ 
i^^ plug^ rgum exuded anil in most cases typical Botrytis gummosis lesipns 
f[developed around the place of injury. 
The results of these experiments appeared to show that injuries in 
^cmselves were not sufficient to induce gum formation. When the 
; injuries were contaminated with pure cultures of Botrytis cinerea, however, 
uuder i the [Same conditions, gum formation and death of the tissue 
readily toph: place. Other injuries of various kinds also failed to induce 
gummiUg in most cases even when no means were provided to keep the 
? wounds free from chance contaminations from the air or from water 
; during rains. These same wounds, however, when purposely infected 
with Botrytis cinerea or other injurious organisms resulted in gum forma¬ 
tion. Mechanical pressure and obstructions placed in the conducting 
system likewise failed to induce gum in these lemon trees. In previous 
experiments conducted by Fawcett {22), clean injuries made by cutting 
through the bark of Prunus persica, Prunus umbellata, Prunus serotina. 
iMurocerasus caroliniana, Xanthoxylum americanum, and Rhus glabra in 
Florida failed to induce gum, but when similiar injuries in all these 
species were inoculated with Diplodia natalensis, gum formation resulted. 
