REPORT OF THE SOCIETY 119 



The above discribed pathological histology differs from that given by Van 

 Hall (10) in two main points; — First, he states that the starch grains are not 

 destroyed by the invasion of the bacteria, and second that the bacteria are una- 

 ble to enter the cells, that is, they are entirely intercellular. In egard to the 

 first point, in all the diseased sections that were examined by the writer, in not 

 a single case were the starch grains found to be intact. With regard to the 

 second difference, the writer was able to obtain photomicrograph which defini- 

 tely showed the bacteria in the cells. Whether the bacteria penetrated the wall 

 and thus entered the lumen of the cell, or whether they entered after the wall 

 was ruptured, the writer is not able to state. The bacteria may not enter the 

 cell till after the wall is ruptured, but in any case it is the toxine (Van Hall (10) 

 produced by the invading pathogen that causes the breaking down of the wall; 

 and even if the organisms do not enter the lumen till the wall has been ruptured, 

 the fact remains that they do enter the cell, and are, therefore not strictly inter- 

 cellular. 



Summary. 



1. Bacterial rhizome rot of Iris is increasing in importance in this part of 



the country. 



2. The organisms causing soft rots are parasitic on a wide range of plants. 



3. The complete geographical distribution of bacterial soft rot of Iris is not 



known, but the disease is probably wide spread. 



4. This disease is economically important on account of its destructiveness to 



large numbers of valuable Iris plants. 



5. The disease is a typical soft rot destroying the rhizome parts attacked as 



well as the foliage. 



6. Thirty-six organisms were isolated from various sources and different inocu- 



lation tests carried out which resulted in the obtaining of typically 

 diseased plants by inoculation with two of the organisms used. 



7. The two pathogens finally "proved up" by the writer react on various 



media in a similar manner to B. Carotovorus and are believed to be forms 

 of thdt species. 



8. Smith (9) states that B. Oleraceae, B. omnivorus and B. Apivorus are appa- 



rently identical with5. Carotovorus. The writers' work shows that the 

 disease in Quebec is caused by a form of B. Carotovorus. If the view 

 of Smith is correct, it appears that the disease in Quebec and in Europe 

 is caused by similar organisms. 



9. The pathogen destroys the host by a dissolution of the middle lamellae 



of the cells, a gradual destruction of the cell contents, and finally a 

 total disintegration of the diseased tissues. 



This article is an abridgment of a thesis taken under Dr. B. T. Dickson in 

 the Department of Botany, Macdonald College, and submitted to the Gra- 

 duate School of McGill University in partial fulfilment of the requirements for 

 the degree of M, Sc. 



The writer wishes to acknowledge his appreciation to Dr. Dickson for help- 

 ful suggestions and constructive criticism, to Dr. Hood of Macdonald College 

 and Dr. L.-R. Jones of Wisconsin for cultures which they supplied and to Mr. 

 J. P. Spittall for his translation of German references. 



Contribution No. 20 Dept. of Botany, Macdonald College, Que. 



