Dec. i S , 1920 Effect of Temperature and Humidity on Citrus-Canker 505 



control it when it is parasitically active in the host plant. Likewise, 

 the conditions necessary for initial infection of the plant differ. 



(6) The period of initial infection must be clearly distinguished from 

 the period of incubation and subsequent development of the disease. 



(7) The conditions which bring about the most active growth of the 

 host plant are also responsible for the most rapid development of the 

 disease. 



(8) The difference between host plants in their temperature and 

 humidity relations, in both the greenhouse and field, is further brought 

 out in their behavior toward infection and the development of the 

 disease. 



(9) The organism is active in the tissues so long as the host cells are 

 active, and when the plant is forced into dormancy the organism becomes 

 inactive and the disease is then quiescent. 



(10) Environmental conditions play an exceedingly important role in 

 the susceptibility and resistance of Citrus plants to canker. 



(11) The results indicate that it will be necessary to study the behavior 

 of the host plant in its environment and its relation to the causal organism 

 before any scientific selection or breeding for disease resistance can be 

 made. 



LITERATURE CITED 



(1) DoidgE, Ethel M. 



1916. THE ORIGIN AND CAUSE OP CITRUS-CANKER IN SOUTH AFRICA. Sci. Bui. 



Union So. Afr. Dept. Agr. no. 8, 20 p., illus., 10 pi. Literature cited, 

 p. 18-19. 



(2) HassE, Clara H. 



191 5. PSEUDOMONAS CITRI, THE CAUSE OP CITRUS-CANKER. A PRELIMINARY 



report. In Jour. Agr. Research, v. 4, no. 1, p. 97-100, pi. 9-10. 



(3) Harding, H. A., Stewart, F. C, and Prucha, M. J. 



1904. VITALITY OF THE CABBAGE BLACK ROT GERM ON CABBAGE SEED. 



N. Y. State Agr. Exp. Sta. Bui. 251, p. 175-194, 1 pi. 



(4) JEHLE, R. A. 



1916. means OF identifying citrus-canker. In Quart. Bui. State Plant 



Bd. Fla., v. 1, no. 1, p. 2-10, 12 pi. (partly col.) 



(5)- 



191 7. CHARACTERISTICS OF CITRUS-CANKER AND OF THE CAUSAL ORGANISM. 



In Quart. Bui. State Plant Bd. Fla., v. 1, no. 2, p. 24-27, illus. 



(6) MackiE, D. B. 



1918. some observations ON citr us-cankER. In Cal. Citrograph, v. 3, 



no. 10, p. 231, 244-245. 



(7) Peltier, G. L. 



1918. susceptibility and resistance to citrus-canker of the wild 

 relatives, citrus fruits, and hybrids of the genus citrus, 

 preliminary paper. In Jour. Agr. Research, v. 14, no. 9, p. 337-357. 

 pi. 50-53. Literature cited, p. 356-357. 



