478 Journal of Agricultural Research vol. xx. no. 6 



At 20 C. the spots which developed were more or less typical of 

 those produced under natural conditions. At 25 and 30 , however, 

 they were extremely soft, loose, and spongy. These differences were 

 due to the stimulating influence of the high humidity and temperature. 



EXPERIMENT 2A 



In reality, this experiment is made up of two parts: First, the influ- 

 ence of temperature on infection of the plants at 5 , io°, and 15 C, 

 with the subsequent transfer of the bell jars, together with the plants, 

 to the 30 case; and secondly, the infection of the plants at tempera- 

 tures between 20 and 30 . 



At the end of a 15-day period, the plants held at the temperatures 

 of 5 , io°, and 15 C. were transferred to the 30 case to see, first, if 

 the shock would force growth of the dormant plants, and secondly, if 

 canker would develop, for during this period no spots appeared at any 

 of these temperatures. The appearance of new spots after the transfer 

 is noted in Table VII, while the number and type of spots, with the 

 part and age of the host attacked are given in detail in Table XII. 



All the actively growing citranges became diseased soon after the 

 transfer. The two plants which remained dormant stayed clean. In 

 all cases, canker was confined to the new growth. It will be seen that 

 most of the citrange plants developed at a normal rate after the transfer 

 to the higher temperatures. The spots after breaking out were not 

 scattered over the new leaves and twigs but on definite portions of 

 the leaves, principally at the tip, along the midrib of the leaf and petiole, 

 and, in case of twig infection, along one side in regular arrangement. 



Unpublished experiments with grapefruit seedlings and plants, in 

 both the greenhouse and field, on the time required for initial infection 

 have shown that the organism was able to enter the leaves within 20 

 minutes. Apparently, when the organisms were sprayed on the plants, 

 they were able to enter the stomata and there lie quiescent. The cit- 

 range plants were either just starting growth or were dormant when 

 inoculated and remained so until transferred. When the plants were 

 shifted from the 5 , io°, and 15 C. cases to 30 , the majority of them 

 pushed out into rapid growth, and the organisms also started to develop. 

 As the leaves unfolded and the twigs grew in length the spots broke 

 out where the organism had entered the tissues, which, as is stated 

 above, occurred at definite points on the new growth. The spots 

 appeared on the plants in from 5 to 8 days after they were placed in 

 the 30 case. 



No canker developed on the calamondin plants when they were taken 

 from the 5 Cease and kept at a temperature of 30 . Only two plants 

 making a rapid growth after being placed at a temperature of 30 from 

 the io° and 15 cases became diseased. The others remained free 

 from canker. Both the plants which later became diseased were in a 



