246 
Journal of Agricultural Research voi. xxviii, no. 3 
classed as late, the season of 1918 as extremely early, while the remainder were 
more or less normal. 
When the temperature is correlated with the appearance of new growth in 
Alabama, grapefruit plants are forced into new growth at any time after the first 
of the year when a weekly mean temperature of 59° F. or above prevails. For 
the trifoliate orange and Satsuma, a weekly mean temperature of above 65° F. 
is necessary. 
Not all plants of the same variety start growth at the same time in the spring. 
Thus, we not only have various species starting at different times, but even 
plants of the same variety. It is also a well-known fact that, the first spring 
growth is usually smaller than that produced during the succeeding growth 
periods. The leaves formed are also smaller and mature more rapidly. Thus 
the amount of spring growth formed and the rapidity with which it matures are 
also dependent on the prevailing weather conditions. 
Table I.— Weekly mean temperatures from January 1 through June 10, for 7 
years at Mobile, Ala. 
Month 
1914 
1915 
1916 
1917 
1918 
1919 
1920 
Jan. 1- 7_ __ 
o p 
44.0 
° F. 
51.0 
o p 
63.0 
o p 
61.0 
o p 
44.0 
o p 
40.0 
° F. 
49.0 
8-14__ 
51.0 
48.0 
54.0 
53.0 
41.0 
47.0 
53.0 
15-21. 
60.0 
53.0 
49.0 
53.0 
43.0 
53.0 
61.0 
22-28____ 
58.0 
44.0 
61.0 
57.0 
50.0 
57.0 
54.0 
20-Feb. 4. 
56.0 
53.0 
57.0 
50.0 
50.0 
55.0 
56.0 
Feb. 6-11______ 
53.0 
51.0 
60.0 
45.0 
58.0 
49.0 
57.0 
12-18.. 
52.0 
56.0 
52.0 
56.0 
62.0 
53.0 
48.0 
19-25....... 
51.0 
54.0 
54.0 
58.0 
60.0 
59.0 
59.0 
26-Mar. 4.... 
48.0 
51.0 
54.0 
68.0 
68.0 
56.0 
44.0 
Mar. 5-11...... 
53.0 
52.0 
56.0 
56.0 
68.0 
58.0 
44.0 
12-18.... 
54.0 
54.0 
54.0 
67.0 
65.0 
65.0 
62.0 
19-25.... 
50.0 
48.0 
68.0 
63.0 
65.0 
65.0 
62.0 
26-Apr.l_____ 
68.0 
58.0 
62.0 
65.0 
64.0 
59.0 
67.0 
Apr. 2- 8..... 
67.0 
54.0 
64.0 
62.0 
69.0 
63.0 
64.0 
9-15...... 
60.0 
67.0 
59.0 
61.0 
55.0 
69.0 
61.0 
16-22... 
68.0 
72.0 
69.0 
69.0 
69.0 
64.0 
72.0 
23-29_____ 
74.0 
73.0 
67.0 
73.0 
69.0 
70.0 
68.0 
30-May 6.. 
76.0 
75.0 
68.0 
69.0 
69.0 
72.0 
73.0 
May 7-13______ 
73.0 
71.0 
78.0 
63.0 
75.0 
73.0 
72.0 
14-20. . . 
72.0 
78.0 
77.0 
69.0 
75.0 
73.0 
72.0 
21-27..... 
75.0 
80.0 
77.0 
77.0 
79.0 
68.0 
80.0 
28-June 3...... 
80.0 
77.0 
82.0 
79.0 
79.0 
75.0 
77.0 
June 3-10. 
83.0 
82.0 
sa 0 
80.0 
sa 0 
81.0 
77.0 
ON THE DISEASE 
Judging from the results obtained under controlled conditions, we would 
expect initial infection to occur in the field on young growth during periods 
when free moisture was present on the surface of the leaves between tempera¬ 
tures of 59 and 74.3° F. Initial infection would be most abundant under these 
conditions when a temperature of about 68 to 70° F. prevailed. 
Observations point to the fact that the spores of the pathogene overwinter on 
the leaves in the old scab spots formed during the preceding season. At least 
these old scab spots serve as the chief source for the early spring infections. 
Judging from the many observations made in the field, it appears that the spores 
of the fungus may also lodge in the scales of the dormant buds and then when 
these begin to grow in the spring the spores are at hand to produce infection on 
the young unfolding leaves. 
The presence of free moisture on the surface of the leaves is necessary for a 
rather long interval for the successful germination of the spores to take place 
and for the germ tube to enter the tissues of the leaf. Even after the hyphae 
