Aug. 26,19x8 Susceptibility and Resistance to Citrus-Canker 
339 
At the time of the first inoculation, August 27, 1917, the plants in 
the two large cases were thoroughly sprayed with two 48-hour-old 
(100 cc.) cultures of P. citri in beef bouillon. A similar (100 cc.) culture 
was used for the smaller case. On September 12 the plants were again 
sprayed with half the amount of solution used above. The plants were 
removed on October 13 to a large screened case. The same day a second 
lot of plants were set in the cases and inoculated. These plants were 
again sprayed with 48-hour-old cultures of P. citri in beef bouillon on 
October 23 and November 1. The plants remained in the cases until 
January 13, when they were removed to the screened case where they 
are at the present time. Thus, the plants in Experiments I and II have 
been exposed to the Citrus-canker organism for a period of six months 
(February 27) and five months (February 12), respectively. 
Conditions governing inoculations. —During the course of the 
experiments a relatively high temperature has been maintained. On 
one or two nights during the cold weather the temperature dropped to 
40° F., but the night temperatures averaged 6o° and higher. During 
the day a temperature of approximately 90° and higher has prevailed 
the greater part of the time. Occasionally it dropped to 70° and at 
other times was nearer 95 0 . However, with these variations, a tem¬ 
perature has been maintained which, with other factors eliminated, 
made possible a maximum amount of infection. 
Practically a 100 per cent humidity was kept in the cases. About 
once a week the plants were given a thorough spraying with a strong 
water pressure, a measure that would assist in distributing the canker 
organism. After the plants were transferred to the screened cage, they 
were sprayed on an average of twice a week. This spraying was carried 
out early in the morning, so as to produce a condition somewhat similar 
to a heavy dew. So far as humidity was concerned, then, infection was 
possible practically all of the time. The facts that numerous spots 
developed and that leaves were defoliated by canker in the screened case 
during the winter proved that these conditions were ideal for infection. 
Another point that might be mentioned is that the plants were exposed 
to rather strong sunlight, as only a very light shade was used on the 
glass of the house. 
Early in the work it was found that, even though ideal conditions of 
temperature and humidity were supplied for infectiort, few or no canker 
spots developed if the plant was not in good growing condition. The 
largest number of spots naturally occurred on mature leaves which were 
still tender and of a light-green color. Few spots appeared on the 
young leaves, while spots developed on the old foliage of the more sus¬ 
ceptible plants only. Thus, it is a hard matter to fix any definite scale 
of susceptibility or resistance for a comparison of the different plants, 
especially when so many types are represented. However, by comparing 
