Apr. 21,! J933 
Gummosis of Citrus 
225 
In Prunus and other plants, however, mechanical injuries in them- 
selv^ have been considered as sufficient to induce gum formation. But- 
{^3) was successful in inducing gum formation on peach, cherry, and 
plum by bruising the bark with a mallet. No mention is made of similar 
experiments on Citrus. 
The injuries on Citrus made by a number of insects are frequently 
followed by gumming, usually slight in amount. Small drops of gum 
may form on fruit at points of injury produced by the orange tortrix 
{Tarim ci^ana)y and on small tree trunks and limbs by grasshoppers, 
katydids, and other insects. To what extent this gumming may be due 
to secretions of the insects and-to what extent to the entrance of micro¬ 
organisms at the time of injury is uncertain. Our negative results from 
meehamcal injuries on Citrus kept sterile and free from chemical stimuli 
would indicate that this gumming was probably not due tO; the injury or 
wound in itself. 
BURNING 
14 tbe aiitlipr’s expenehce, burning was not in itself ^y more effective 
ill producing gum formatfoh iti Citrus. The 
fl^e oj^ ah alcoho^ was held against the trunk of yoiihg Citrus 
trees uhtil .the was severely injured, but no gumrhing resulted. 
Exam’inhtipn of many Citrus trees that have been accidentally injured by 
fife has shoWh jthat bark may be killed on one side of ihdgs' ^ branches 
\yithout r^^ in gum formation. Severe injuries from SUnbuming 
on Citni^' nave also been observed to be free from giim foimation, pro- 
yid^ they ath followed by invasion of parasitic 6r'wbod-rotthig 
organisms. ' (jj), however, reports the production of on 
ypiuig shoots of Prunus by burning with a hot iron. ‘ ^ 
V rRBBZING ^ . i 
Freezing has also been considered a frequent cause of gum formation. 
Observations of hundreds of Citrus trees in California in all stages of 
injury from frost have not indicated that freezing in itself is an important 
factor in initiating guih formation. Frost injury, however, may fre- 
qu^tly be followed by invasion of organisms such as Botrytis cinereay 
or other fungi, which after becoming established in 
the injured tis^e may advance rapidly and induce gumming in tissue 
apparently sound. 
DJ^ICCATION 
Drying or partial desiccation of cells in plants has been suggested as 
ah impoartant factor in gum formation. As the result of a number of 
controlled experiments with species of Prunus, drying of the tissue was 
considered by Higgins (40) as an important factor in the acceleration of 
gum formation, i Sorauer (59, />. yo 8 ) cites Martin as mentioning the 
action of dry desert winds of autumn and winter as having a relation to 
gum formation in Acacia Senegal, It has been pointed out by Mac- 
Dougal, Richards, and Spoehr (47) that when Opuntia plants, are sub¬ 
jected to long periods of drought, resulting in partial desiccation, the 
sugars, which have a low water-holding capacity, are converted into the 
pentosans or mucilages, which have a high imbibition capacity. 
That this factor of partial desiccation operating alone can^ not account 
for excessive gum formation in Citrus seems to be indicated by the fact 
that such gum formation does not necessarily follow injuries from frost 
