io Research Bulletin No. g 



F. trichothecioides or F. tuberivorum as representative of the 

 parenchyma-invading section (Discolor). Since it was desirable 

 that the identity of the organisms be well established, the writer 

 asked Mr. W. A. Orton, in whose laboratories Dr. Wollenweber 

 had carried out his recent work, for cultures of the organisms. It 

 was impossible to get cultures which had been authenticated by Dr. 

 Wollenweber, since he had gone to war, but through the courtesy 

 of Mr. Orton, Mr. Carpenter (Dr. Wollenweber's assistant) 

 furnished a strain of F. trichothecioides (no. 41, 1916) and a strain 

 of F. oxysporum (no. 3345A). The other strains of F. trichotheci- 

 oides used had been isolated by the writer in 191 1, and were 

 described as F. tuberivorum. Several strains of F. oxysporum 

 isolated from Nebraska potatoes were also used. 



Pure cultures of these organisms were maintained on sterilized 

 rice in plugged Erlenmeyer flasks, and these were used as a point 

 of departure for all the work recorded. 



I. Infection experiments 



(1) EXPERIMENTAL infection of tubers 

 Tubers of the Early Ohio and Red Cobbler varieties were used 

 in these experiments. Only sound tubers were selected, and these 

 were thoroughly cleansed and sterilized before infection. At first 

 they were sterilized by the formaldehyde gas method recommended 

 by Wollenweber (41). Several difficulties were encountered in 

 using this method. It was found very difficult to remove the last 

 traces of the gas without contaminating the chamber, and the tubers 

 often showed the characteristic formaldehyde vapor injuries that 

 have been discussed in bulletins of the New York Experiment 

 Station (13, 37). Consequently, the writer abandoned the first 

 method and sterilized tubers by immersing in 1 : 1000 HgCl 2 solu- 

 tion for 1.5 hours. Inoculation was carried out by removing a 

 piece of the cortex with a sterile cork borer, placing an infected 

 grain of rice into the hole, and then replacing the piece of tuber 

 tissue. The wound was then sealed with sterile grafting wax and 

 the tuber placed into sterile chambers. This proved an efficient 

 and convenient way of carrying out the great number of experi- 

 mental inoculations made. 



