98 



suiting Ironi [hv tiilargcnicnl oT cells causes the rupture 

 of the epidermis and the exposure to desiccation of the 

 cankerous cells. Such cells are only lightly attached to 

 each other as shown in fig. 5, and will separate intact in 

 a drop of water on a slide when spongy cankers, plate 

 2, fig. 2, are examined. The hacteria are normally 

 found to occur hetween the cells and not within them, 

 as stated by Hasse. 



Several causes operate in bringing about the enlarge- 

 ment and separation of cankerous cells. Among them 

 are (1) the presence of the bacteria between the cells 

 with the consequent passage of materials which are 

 used in the growth of the bacteria, through the host 

 cell walls, (2) the bacteria dissolve the middle lamellae; 

 (3) they dissolve starch and otherwise affect the cell 

 contents so that diseased cells have a greater afTmity 

 for water. 



Death of diseased cells results in part from drying 

 after the rupture of the epidermis and the cell walls 

 gradually become suberized. 



I-"ig. ."). Spongy canker in outline on rind of 

 grapefruit sliowing enlargement of cells 

 and indicating the ease with which they 

 may be separated. 



A chemical analysis of diseased and of healthy 

 grapefruit leaves by the employment of a refined meth- 

 od of analysis shows that there have been in cankerous 

 tissues ])roround changes, especially in the carbohy- 

 drate and nitrogenous substances. It was also found 

 that there is a decrease in acid content in diseased 

 tissues. An attempt was made to correlate the differ- 

 ence in acidity of grapefruit leaves and Satsuma leaves 

 with the diffei-ence in suscei)libility of these two species 

 to canker. Satsuma leaves are consistently higher in 

 acid content than grapefruit leaves, but the difTcrence 



