Journal of Agricultural Research voi. xxiv. No. 3 
198 
containing lemon fruits. The Py^iacystis will enter the fruit and pro- 
due^ brownrot, leaving the associated organisms behind. It may then' 
be isolated more easily as a pure culture from bits of the infected fruit. 
After the discovery that Pythiacystis citrophthora was capable of 
inducing the disease it remained to be shown that this fungus was com¬ 
monly present in connection with this type of gummosis. Accordingly, 
a survey was made of various Citrus localities in California. During the 
investigations (1912-1916) P. citrophthora was isolated 109 times from 
the diseased bark of 68 Citrus trees, representing about 30 different 
orchards in 10 counties of California, extending from San Diego on the 
south to Butte County on the north. It was also isolated from one 
locality in Arizona (Table I). In addition, the fungus was reisolated in 
40 different cultures from 20 cases of gummosis produced by inoculation. 
Tabi.® I .—Isolation of Pythiacystis citrophthora from gummosis lesions from natural 
infections 
Variety. 
Season. 
Number of 
localities. 
Number of 
trees. 
Number of posi¬ 
tive cultures. 
f Spring. 
2 
14 
19 
20 
21 
Lemon. 
\ Summer. 
8 
32 
25 
12 
[Fall. 
6 
rSoring. 
e 
5 
A 
Sweet orange. 
< Summer. 
j 
A 
0 
[Fall... 
*T 
2 
*T 
A 
y 
A 
Pomelo. 
/Winter. 
I 
*T 
I 
‘T 
A 
1 Spring. 
*T 
I 
I 
2 
These 109 cultures were obtained from 53 lemon trees, 13 sweet-orange 
trees, and 2 pomelo trees. All of the lemon, 9 of the sweet-orange, and 
the 2 pomelo trees were affected with typical gummosis of the trunks 
with the invaded portions of bark extending some distance above the 
surface of the soil. Four of the orange trees had lesions low down, near 
or upon the main roots, as is typical of mal di gomma or footrot lesions. 
Although many isolation culture tests were made from various por¬ 
tions of ^e affected bark, including the outer gummous zone, and even 
some of the imaffected tissue, all of the successful isolation cultures 
except ope were obtained from the advancing margin or outer fringe of 
the invaded zone. Isolation tests were made every month in the year 
except during January and February, and cultures of the fungus were 
obtained during each of the 10 months. The secondary organisms most 
commonly obtained in cultural tests from the older portions of the 
invaded zone back of the margins were species of Fusarium, Alternaria, 
Cladosporium, and Colletotrichum, and a large number of bacterial 
species. 
INOCUI.ATIONS WITH DISBASBD TISSUB 
Even before the causal fungus was discovered the infectious nature 
of the disease was determined by means of a large number of inocula¬ 
tions with diseased bark, the results of which are represented by the 
following typical examples. 
On'February 27, 1912, at Chula Vista in San Diego County, the follow¬ 
ing inoculations were made on 16-year-old lemon trees in heavy soil. 
The inocula w^e inserted into vertical cuts about 2 cm. long, made 
