28 Sttidies in Bacteinosis 



tissue and the nature of the cell contents are identical in the raised and 

 depressed areas; and, as will be described later, an organism has been 

 isolated from the dead tissue of one type of spot which on inoculation 

 into a healthy leaf has given rise to a spot of the other type; there is 

 therefore no doubt that both types of spot have a common origin. It is 

 not known whether the one changes into the other, or whether they are 

 the result of difference in age of the leaf at the time infection took place. 

 Spots of both types occur on one and the same leaf and may be recog- 

 nised in the photograph (Fig. 1 A) ; the sunken type with bright red 

 colour (Fig. 1 B) is, however, the only one which has resulted from 

 artificial infection of young seedling plants (Fig. 2). For these figures 

 see Plate II. 



Pathological Anatomy. 



Microscopical examination of a section through one of the spots shows 

 the cells completely disorganised, the normal contents having given place 

 to a yellow or brown gum-Hke mass. In fresh material the mass com- 

 pletely fills the cavity of the cell, but in fixed material it is found to have 

 contracted slightly from the walls of the cells (Figs. 4 and 5). The group 

 of affected cells is frequently cut oft" from the surrounding tissue by a 

 zone of three or four layers of cork cells. No fungal mycelium is present 

 in the diseased tissue, and no bacteria can be found in the intercellular 

 spaces. In many spots clear evidence of the parasitic origin of the 

 disease is lacking, but in others one or two cells, usually epidermal cells, 

 are found filled with granules which have all the appearance of micrococci 

 and which take the bacterial stains strongly (Fig. 3). In these cells the 

 gum-like substance is either absent altogether or is present in such small 

 quantity that only a very faint yellow colour is observable. In the 

 7Tiajority of the diseased cells, however, this substance is present, and 

 exhibits a variety of differences in its minute structure and staining 

 capacity which are thought to have considerable significance. An attempt 

 to reproduce these differences by shading has been made in Figs. 4 and 5 ; 

 the drawings are from a hand section through a "blister-spot," and the 

 section was stained with carbol fuchsin and partially decolourised with 

 50 per cent, alcohol^. 



The substance in some cells retains the fuchsin strongly and includes 

 a mass of closely compacted granules which stain still more strongly with 

 fiiclisiii and other bacterial stains. Fig. 5 shows several such masses. 



' The similarity in actinic value of the red and oianire rays makes it imj)ossil)l<' to 

 demonstrate these ditTeroncos of colour and structure ijy a photographic process. 



