Apr. ax, 1923 
Gummosis of Citrus 
201 
Experiments were made (i) by inserting pieces of lemon fruits affected 
with the brownrot into incisions made in the bark of healthy lemon 
trees; (2) by placing similarly affected lemon fruits in contact with the 
roots or trunks of healthy lemon trees and covering them with moist 
soil; and (3) by placing affected lemons, as in experiment 2, at the root 
or trunk of orange trees budded on both the sour- and the sweet-orange 
stocks. 
In a typical experiment of the first kind, a piece of diseased lemon rind 
was inserted into a cut in the bark of a 19-year-old lemon tree 20 cm. 
above the sweet-orange stock, on February 26, 1913. A control cut not 
inoculated healed rapidly without gumming, but in 45 days the inoculated 
cut showed definite evidence of infection. The killed bark area enlarged 
from 4 by 7.5 cm. in 70 days to 28 by 82 cm. in about 13 months after 
inoculation (PI. 2, A, B, C). In about 18 months the killed area reached 
extreme dimensions of 35 by 125 cm., one-third of this length being upon 
the sweet-orange stock (PI. 2, D); the leaves were now yellow and drop¬ 
ping on the affected side. Cultures were made from the bark and Pythia- 
cystis was obtained, but only at the advancing discolored margins of the 
area where the bark was killed through to the wood. Specimens taken 
from other places in the diseased tissue, and from the live tissue just 
outside the diseased areas, either yielded other organisms or were sterile. 
Among the organisms found both inside and outside the area of recent 
invasion were species of Colletotrichum, Alternaria, and Cladosporium, 
and also species of bacteria. 
The disease having been produced by inoculation from diseased fruits 
into cuts in the bark, it now became of interest to determine whether 
infection could originate from diseased fruit placed near uninjured bark. 
On May 13, 1913, at Whittier, several lemon fruits affected with 
Pythiacystis-rot were buried in the soil near the trunk of a small lemon 
tree growing in a large earthen pot. The soil was heaped up against the 
trunk and kept moist by frequent watering. A similar tree in another 
pot received the same cultural treatment without the diseased fruit. 
During the summer of 1913 no results of infection were noted. When 
next examined, in March, 1914, the first tree was seen to be badly affected 
with typical Pythiacystis gummosis, while the control tree remained 
healthy. 
In other tests on lemon and sweet-orange trees with decayed fruits, 
infection leading to Pythiacystis gummosis frequently but not inva¬ 
riably resulted. Sour-orange trees under the same conditions whether 
injured or uninjured failed to contract the disease. 
These tests, taken in connection with numerous observations in 
orchards, show that the sour-orange tree is highly resistant to Pythiacystis 
gummosis and that sweet-orange and common-lemon trees, though easily 
infected through injuries, are not otherwise readily infected except under 
the most favorable conditions for invasion by the parasite. 
INOCULATION WITH PUR® CULTURES OP PYTHIACYSTIS CITROPHTHORA, AND 
REISOLATION 
As a result of a large number of inoculations from pure cultures of 
Pythiacystis citrophtkora, it was shown that this fungus was capable of 
invading the bark and bringing about all the characteristic effects that 
have been noted in naturally occurring cases or those produced by 
