Dec. 15, 1920 Effect of Temperature and Humidity on Citrus-Canker 469 



The plants which served as controls all made a rapid growth. At 

 1 5 C. the plants were all inhibited in their growth, there being practi- 

 cally no change during the interval the plants were held at this tem- 

 perature. The leaves of the large grapefruit plant grew slowly and 

 began to mature. 



Immediately on being transferred back to the 30 C. case, all but one 

 plant proceeded to grow rapidly at the normal rate for this temperature. 

 Thus, a temperature of 15 has a very decided inhibiting effect on the 

 growth of Citrus plants, much more so than in experiment 3, where the 

 plants were subjected to a temperature of 30 during the day and 15 

 and lower at night. 



EXPERIMENT 5 



In the preceding experiments, it has been clearly demonstrated that 

 the most growth of all Citrus plants tested occurs at 30 C. Likewise, 

 the best development of the organism in culture occurred at this same 

 temperature. Above this temperature, growth of the organism was more 

 or less inhibited. Thus, to determine what effect temperature higher 

 than 30 would have on the growth of the plants, the following experi- 

 ment was carried out. Plants in various stages of growth, as shown in 

 Table X, were divided into four sets and placed in a saturated atmosphere 

 under bell jars at a temperature of approximately 35 . The results show 

 very decidedly that grapefruit and the other plants of this same type 

 were distinctly inhibited by this temperature, even though actively 

 growing plants were used. However, after they were transferred to the 

 30 case, the young growth started out at the normal rate for that tem- 

 perature. 



On the other hand, the trifoliate orange and limequat 1 plants made 

 a good growth at 35 C. It is interesting to note that this is just the 

 opposite of the result obtained at lower temperatures. Grapefruit was 

 able to make a slow growth at 15 , while the trifoliate orange and 

 calamondin plants were unable to develop at all. 



1 A hybrid between Citrus aurantifolia, West Indian lime, X Fortunclla japonica, round kumquat. 



