- 
17,4 Lee: Fungicides and the Citrus-canker Organism 335 
stronger dilutions for the longer periods of exposure. It seems 
probable, in the light of later tests, that killing was due, not to 
the copper compounds, but to a slight excess of lime resulting 
from an imperfect manufacture of “neutral’’ Bordeaux mixture. 
In any event the tests show that neutral Bordeaux mixture had 
little or no toxic action against the citrus-canker bacteria, in con- 
trast to a more pronounced action exhibited by Bordeaux 4—4—50 
mixture. Following out the suggestion from this, Bordeaux 
4—6-50 mixture was tested. The results are presented in 
Table 10. 
TABLE 10.—Results of exposures with 3-day-old culture of Pseudomonas 
citri in dilutions of Bordeaux 4-6-50 mixture. 
[Date of test, July 24, 1920; date of observation, July 29, 1920.] 
Dilution expressed in percentage. 
Exposure. 
10. | 20. | 30. | 40./| 50. | 60. | 70. | 80. | 90. | 100. 
Min. sec. 
2 30] a+ os _ os _ _ _ — — | be 
5 00; — _ — — _ _ — _ uo | ee 
7 30); — — rans as ~ _ — ~ - - 
10 00; — _ “ea — se od aa ee a Sa 
12 80; — — =_ ~ _ = — _ - _ 
15 00; — a oe = — = —_ gr — es 
® Tested on potato, July 26; positive, July 29. 
> Bouillon tested by inoculation with P. citri, July 26; positive, July 29. This shows that 
the medium was not toxic to the organism. 
This test was made four times with closely agreeing results. 
The evidence in regard to Bordeaux mixtures, then, showed that 
neutral Bordeaux mixture was valueless as a toxic agent against 
Pseudomonas citri; that Bordeaux mixture 4—4—50 was of slightly 
stronger bactericidal action; and that Bordeaux: 4-6—-50 was 
much the strongest of the three preparations. It was believed at 
first that this was because of a different copper compound, 
formed in the presence of an excess of lime, from that formed 
by the use of lime sufficient to make only neutral Bordeaux 
mixture. Tables 11 and 12 yield evidence upon this hypo- 
thesis. 
The results were entirely unexpected, but have been corrobor- 
ated by frequent tests. Comparing the results with those ob- 
tained from copper sulphate it is apparent that of the two 
constituents of Bordeaux mixture, quicklime when freshly 
slaked has at least as great a bactericidal value as copper sul- 
phate, if not a greater. According to these tests a 0.1 per cent 
