96 



Life History. 



So far as is known Pseiulonionas citri passes its 

 entire life cycle under natural conditions within the 

 host tissues. New infections appear in spring shortly 

 after the new growth has begun. The first appearance 

 in Alabama was on May 11th in 1914 and on May 27th 

 in 1915. Old cankers on leaves and twigs are undoubt- 

 edly the source of infection in spring since new leaves 

 formed near such old cankers are especially liable to 

 first become diseased. Infections occur not only on new 

 growth but on old leaves and twigs. Old diseased 

 areas may enlarge b}-^ the renewed growth of the or- 

 ganism at the margin of the old cankers. New infec- 

 tions may appear at any time throughout the growing 

 season and have been observed to occur as late as in 

 the month of November. It is not known how long 

 the organism can remain viable under natural condi- 

 tions on fallen leaves, but it is believed that it can sur- 

 vive the winter. It appears to have perished in the 

 laboratory in packets of leaves kept from Septemljcr 

 until May in one case, and from March until October in 

 another. 



Stevens (1) found tlial Ihe canker organism was not 

 only alive but also actively growing in inoculated test 

 tubes of soil kept in the laboratory for six months. 

 That it remains alive in the soil is indicated by the 

 appearance of diseased sprouts from the roots of dis- 

 eased trees which are burned. 



Infections occur through natural openings, breathing 

 pores on the leaves and twigs, and through wounds. 

 It was observed in the inoculation experiments that 

 infection appears first on the lower leaf surface, upon 

 which side the slomata occur. From this it was in- 

 ferred that the bacteria enter the leaf through the 

 stomata. That such is the case was established by a 

 study of leaf sections which were fixed 72 hours after 

 inoculation, infiltrated with paraffin, cut and properly 

 stained. This obser\alion is contrary to lliat of Stevens 

 (3) in which he states without giving evidence that the 

 organisms are capable of ])enetrating either surface 

 of the leaf. Infections through natural oi)enings are 

 possible only in Ihe presence of a film of moisture on 

 the host i)arls. Wounds inflicted on leaves and branches 

 by thorn scratches have been observed lo have af- 

 forded entrance to the canker organism, plate 1, fig. 3. 



