194 
Journal of Agricultural Research 
Vol. XXIV, No. 3 
Comes {14) produced gumming in Italy by inoculations with a bac¬ 
terium which he called Bacterium gummis Comes. B, gummis is also 
mentioned by Avema-Sacca (5) in connection with gummosis of Citrus 
in Brazil and by Gandara (jj) in connection with gummosis in Mexico. 
A number of other investigators, among whom were Swingle and Web¬ 
ber (6^), considered the severe gum diseases as probably infectious and 
due to some organism invading the bark, but little work of an experi¬ 
mental nature with Citrus appears to have been done until recent years. 
Fawcett {22 and 2J) showed that a gumming of branches of Citrus in 
Florida was due to the presence of a fungus similar to Diplodia natalensis 
Evans. The same fungus was found by Burger {28) to be the causal 
agent in a twig disease of the peach. 
Not alone in Citrus but in a number of other plants, especially Prunus, 
definite diseases accompanied by large gum exudations have been shown 
in recent years to be due to specific organisms. Among these may be 
mentioned forms of gummosis on cherries reported by Aderhold and 
Ruhland (2), Griffin (57), and Barss {8)\ on apricot and other deciduous 
fruits reported by Barrett (6); and on plum reported by Higgins (jp). 
There have been other investigators who concluded that the severe 
gum diseases in Citrus were due, not to the invasion of organisms, but 
to certain stimuli operating upon the affected parts. Savastano (5/) 
mad^ a comparative study of gummosis in both Prunus and Citrus and 
concluded, because the histology was the same in both genera, that gum¬ 
mosis in Citrus arose largely from wounds or traumatisms. This con¬ 
clusion was in agreement with the views of many previous investigators 
aa to gummosis in Prunus. Among these were Sorauer {58) in Germany, 
Prillieux (50) in France, and others. Savastano, in a number of papers 
in iiccent years on gummosis in Citrus, has modified this earlier view. 
He has distinguished clearly between mere gum formation as a general 
phenomenon and gummosis in connection with definite diseases. In 
one of these later publications {52) he accepts Comes’s (14) conclusions 
as to the bacterial origin of the definite disease type and concludes that 
the aggravating conditions or causes influencing the occurrence of gum¬ 
mosis are lack of light, clayey, water-holding soils, level ground as com¬ 
pared to hillsides, excessive moisture about the roots, wounds from 
grafting or from digging about the roots and so forth. Most of these 
<jontributing conditions are those favorable for gummosis due to Pythia- 
€fstis citrophihora in California, or mal di gomma due to Phytophthora 
/erm/r-ia in Florida. In this connection it is of interest to note that R. 
E. Smith (57) found lemon fruits affected by typical brownrot like that 
Axxt to PyMacystis citrophthora, in a low-lying, poorly drained grove in 
Sicily, Where footrot was very prevalent a^ mentioned by Fawcett (^5). 
Still oth^^ investigators have concluded that organisms are not at all 
involved in the initiation of gummosis but that certain conditions within 
or without the host are solely responsible for the diseases. Bertoni (p) 
in Paraguay appears to have considered Psorosis and a Pythiacystis-like 
form as phases of the same disease and concludes that poor condition of 
nourishment is the primary contributing cause. Later (10) he believed 
that shade, was a corrective for gummosis. Grossenbacher (38) con¬ 
cluded that untimeliness of bark growth in connection with drought and 
low temperatures was related in some unknown way to gummosis of the 
mal di gomma type in Florida. 
