114 PROTECTION OF PLANTS — 1922-23 



were placed under bell jars and kept at 600 70oF. The inoculations were made 

 on April 4th., and at the end of one week all three plants showed definite disease 

 symptoms. 



Since good results had been obtained by using sterile plants for inoculation 

 purposes, it was decided to complete Koch's rules of proof with organisms 7al 

 a^d 191 in this manner. On April 20th., the organisms were re-isolated from, 

 the diseased plants. 



The limited time available made it impossible for the writer to carry on 

 extensive experiments to determine the natural atrium of infection under field 

 conditions. HoAvever, in the many cases of inoculation that were tried by 

 apph'ing the inoculum to the base of the stem without wounding the tissues, no 

 positive instances occurred. Smith (9) states that the most common means 

 of infection is through wounds made in the host tissue by some mechanical 

 means, such as insect punctures. Infections may also occur through lenticels, 

 stoma,ta, etc., but those through mechanical injuries are the most prevalent. 

 The actual atriuni of infection for the soft rot organism is not given, but it seems 

 logical thjat the mechanical injuries at the bases of the shoots are thje chief point 

 for admitting the pathogen to the host. 



Cultural Studies of the Organism. 



The following account of the organism causing the soft rot o^ Iris is by no 

 means exhaustive, but in the time available the writer has attempted to carry on 

 sufficient experimental work to determine the identity of the pathogen. 



The original collection of organisms was obtained from various sources 

 during the summer of 1921 and kept growing on artificial media until used for 

 inoculation experiments 



As has already been described, these organisms were inoculated into slices 

 of raw carrots and also slices of healthy Iris rhozomes. The organisms which 

 proved pathogenic were then used for the plant inoculations and 7al and 19b 

 were the only ones with which the writer was able to produce definite character- 

 istic disease symptoms. 7al was isolated from an infected rhizome slice after 

 inoculation with 7a, which had been previously isolated from a diseased Iris 

 plant at the College. 19b was a pure culture of Bacillus carotovorus obtained 

 from Michigan Agriculltural College. 



Cultures of the pathogen were re-isolated from infected plants and then 

 checked according to the chart compiled by the Society of American Bact- 

 eriologists. 



In order to eliminate any error, Koch's rules of proof were carried put with 

 plants grown under absolutely sterile conditions. From the infected plants 



