132 
The Philippine Journal of Science 
1921 
of temperatures (Table 2) is also taken from the reports of the 
Weather Bureau of the Philippine Government, and represents 
Manila temperatures. 
The temperatures at Manila may be taken as an index of the 
temperatures at both Los Banos and Lamao. The temperatures 
at Lamao and at Los Banos, therefore, are probably favorable at 
all times for the dissemination and the development of citrus 
canker. 
The humidity remains fairly high throughout the months of 
the dry season as is shown by Table 3. 
Table 3 . — Relative humidity at Manila, compiled from the annual reports 
of the Philippine Weather Bureau. 
* 
Month. 
1914 
1915 
1917 
Mean. 
Maxi- 
mum. 
Mini- 
mum. 
Mean. 
Maxi- 
mum. 
Mini- 
mum. 
Mean. 
Maxi - 
mum. 
Mini- 
mum. 
Per ct. 
Per ct. 
Per ct. 
Per ct. 
Per ct. 
Per ct. 
Per ct. 
Per ct. 
Per ct. 
January.- . ... 
76.2 
98.0 
48.5 
78.6 
99.0 
60.5 
77.9 
97.0 
44.0 
February 
73.8 
95.0 
42.0 
69.5 
96.0 
35.5 
78.1 
99.0 
47.0 
March. __ 
68.6 
94.0 
32.0 
70.9 
97.0 
37.0 
73.4 
97.0 
39.0 
April 
70.8 
97.0 
34.0 
66.0 
96.0 
32.0 
75.0 
98.0 
47.0 
May . . 
72.6 
100.0 
38.0 
75.1 
99.0 
39.0 
77.8 
97.0 
45.0 
June . 
81.7 
99.0 
54.0 
75.5 
100.0 
36.0 
83.5 
99.0 
50.0 
July 
85.4 
99.0 
60.0 
83.5 
99.0 
51.0 
85.0 
99.0 
59.0 
August 
83.0 
99.0 
50.0 
87.3 
100.0 
60.0 
84.0 
100.0 
57.5 
September 
87.3 
98.0 
58.0 
86.4 
99.0 
69.0 
88.4 
99.0 
61.0 
October 
79.7 
99.0 
42.0 
85.9 
99.0 
56.5 
87.6 
99.0 
56.0 
November . _. ... 
78.4 
99.0 
44.0 
85.3 
98.0 
52.0 
83.9 
99.0 
47.0 
December 
82.0 
99.0 
48.0 
83.5 
98.0 
51. 5^ 
84.3 
99.0 
48.0 
Although the humidity and the temperature are favorable 
throughout the dry months, it is apparent that canker develop- 
ment is inactive and passive during these months. The explana- 
tion for this inactivity, corroborated by close field observation, 
is that citrus canker apparently is dependent for its dissemina- 
tion upon free moisture on the leaves, in the form of either 
rain or dew. The dry season from December to May, there- 
fore, is a limiting factor in the development of citrus canker in 
the Philippines. The long days of steady, direct sunlight during 
the dry season are also apparently a limiting factor to the spread 
of the canker organism. 
The dry season is correlated more or less with a steady north- 
east monsoon, while the wet season is correlated _ with a south- 
west monsoon. The velocity of these winds can be judged from 
Table 4, also compiled from the reports of the Philippine 
Weather Bureau. 
