118 PEOTECTION OF PLANTS — 1922-23 



gular, loose, granular mass within the cell wall. Later the cell wall disinte- 

 grates until the entire tissue becomes a broken down mass, which will scarcely 

 hold together. 



The absence of bacteria in the primary stages of the disease leads the writer 

 to believe that there is a toxine or enzyme produced by the invading bacteria 

 which is able to cause the disintegrative effet on the host at some distance 

 from the cells occupied by the bacteria themselves. 



In many cases, while examining slides of diseased lissues, the writer 

 observed vascular bundles which were more or less filled with a golden brown, 

 very finely granular material. Whether or not this was due to the effect of the 

 invading organism the writer is unable to state definitely, because all vascular 

 bundles of diseased parts did not contain these deposits. The fact remains, 

 however, that in no case were there any such deposits observed in the healthy 

 rhizome tissues. 



Pathological Histology of Leaves. 



A definite outline of the cells and a uniformity of the structure and arrange- 

 ment is typical of the healthy tissues. 



The first noticeable effect of the pathogen on the leaves is a dissolution of 

 the middle lamellae of the cells, thus allowing them to separate from one another. 

 As the disease progresses, the cell contents become broken down. This disinte- 

 gration continues fairly rapidly until the entire leaf becomes broken down and is 

 held together only by fragments of the vascular bundles. 



When the leaf tissues become watersoaked, the epidermis loosens from the 

 remainder of the leaf tissue and can easily be removed. 



The rotting is not confined to the leaf parenchyma, for the vascular system 

 is also attacked to a considerable extent. Even although the vascular tissue is 

 subject to the destructive influence of the pathogen, it is not so totally suscep- 

 tible and does not become entirely disintegrated even in the final stages of the 

 disease. 



As was the case with the rhizome tissues, most of the damage or at least 

 a large part of it appears to be caused by a toxic substance produced by the 

 invading bacteria, and not by the actual presence of the pathogenic organism. 

 As the writer's time was necessaril}^ limited, no experiments could be carried 

 out to prove this point. Van Hall (10, however, investigated it rather thorough- 

 ly. He took liquid cultures of the pathogen he had isolated, namely B. omni- 

 vorus, and filtered it so as to remove all the bacteria. The filtrate thus obtained 

 which contained no living organisms, was used for inoculating certain Iris plants 

 which later developed light symptoms of the disease. 



