1916] LINK—FUSARIUM 173 
Problem and method of attack 
In the spring and summer of 1914 the writer discussed the 
Fusarium situation as outlined by WOLLENWEBER with Dr. E. M. 
Witcox and Dr. Witi1Am Crocker. The former suggested that 
the whole situation ought to be gone over, and the latter that it 
would be of interest to search for the physiological basis of this 
alleged biological contrast. It is clear that, if the strict categories 
of WOLLENWEBER exist, then potato parenchyma must possess 
either an absolute or an effective immunity toward Fusarium spp. 
of the ELEGANS section, and that Fusarium spp. of the DiscoLor 
section are either absolutely or practically unable to produce vascu- 
lar mycoses or wilts. 
The purpose of this research was twofold: (1) to determine 
whether such a sharp biological contrast exists; and (2) to deter- 
mine what is the physiological basis for such a contrast. Experi- 
mental infections of potato plants and tubers were used for the 
first phase of the problem. It was clear that the second phase might 
involve a great many considerations, such as the structural, com- 
positional, and metabolic nature of both host and parasite, as well 
as the relation of environmental factors to these. The important 
réle played by the structural and compositional peculiarities of the 
potato and the influence of external factors upon these is well 
illustrated by the studies of APPEL and Kretrz (1, 3) on the efficacy 
of the cork layer in checking bacterial invasions of the tuber. 
Considerations of time and equipment limitations made it obliga- 
tory that the scope of the work be limited to a study of a few repre- 
sentative strains of the groups. 
The writer is under obligation to the Departments of Agricul- 
tural Chemistry, Horticulture, and Experimental Agronomy of the 
_ University of Nebraska Experiment Station for the use of materials 
and equipment; to Miss Ernet Beary for help in much of the 
laborious routine; to Dr. FLoreNce A. McCormick for valuable 
help in the anatomical and microtechnical phases of the problem; 
and to Mr. R. A. Dawson for help in preparing the photographs. 
The writer decided to work with F. oxysporum as represent- 
ative of the vascular parasite section (ELEGANS), and with 
