174 BOTANICAL GAZETTE [SEPTEMBER 
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 1911, 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, 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. 
