588 
Journal of Agricultural Research 
Vol. XI, No. ii 
Finally, if we take into consideration the apparently weakened condi¬ 
tion of the fungus in resistant host cells, the change in the nature of the 
protoplasm of the invaded cells, the new cell division, and the formation 
of cork walls around the point of invasion, all of which seem to play a 
part in the prevention of further invasion by the fungus, and all of which 
are due more or less to the chemical reaction of the host protoplasm, it 
seems safe to conclude that the resistance of flax to F. Uni is essentially 
of a chemical nature. 
INHERITANCE OF WILT RESISTANCE THROUGH HYBRIDIZATION 
In undertaking a study of the inheritance of wilt resistance though 
hybridization it was very necessary that highly resistant and susceptible 
strains of flax be secured and thoroughly tested on infected soil before 
making crosses. The object of this chapter is to deal with methods of 
procedure in the work and to give such results as have been obtained 
from crosses up to date. 
METHODS OF SOIL INOCULATION 
Before the progeny from crosses could be tested it was highly impor¬ 
tant that the soil on which the plants were to be grown should be thor¬ 
oughly infected with the wilt-producing organism, F . Uni . The soil sent 
by Prof. Bolley from North Dakota was found by the preliminary tests 
to be satisfactory (PI. 44, B), but the quantity was not sufficient. An 
attempt was therefore made to inoculate soil with pure cultures of the 
organism. In order to try this out, a small flat of greenhouse soil was 
sterilized in an autoclave one half being planted to flax No. 3 (suscep¬ 
tible), and the other half to flax No. 4 (resistant). After planting, 
about half a dozen tube cultures of F, Uni , which were fruiting abund¬ 
antly, were mixed thoroughly in a small pot of water and poured over 
the flat. Wilting of the susceptible plants did not begin until they were 
of considerable size, but they were completely killed in a short time 
after the disease started (PI. 44, C). A large bench of soil was then 
inoculated. Water suspensions of the organism from pure culture were 
poured over the soil and worked into the surface. Seeds of the suscep¬ 
tible strain of flax were planted in abundance in the soil. As more 
fruiting cultures of the organism were obtained, the inoculation was 
repeated. When the plants from this seed showed considerable wilt 
they were turned under the soil and more seed planted. Only three 
or four plantings of this kind were necessary with the pure-culture inocu¬ 
lations to put the soil in suitable condition for the growth of hybrid 
plants (PI. 46, A, B). It was also found that from to 2 inches of the 
North Dakota soil spread over Madison soil was sufficient to produce 
thorough wilting of susceptible plants (PI. 46, C, b). 
