Dec. io, 1917 
Flaxwilt 
575 
naturally arisen the question as to the nature of individual variation 
and the cause of disease resistance. Although there has been consider¬ 
able theorizing concerning the possible cause, or nature of resistance, 
very little intensive research has been directed toward a positive solu¬ 
tion of the problem. Biffen’s (2, 3) hybridization experiments with 
wheat were the first to throw light on disease resistance as being due 
to inheritable factors which behave according to the laws of Mendel. It 
hardly seems possible, however, to explain the inheritance of such a char¬ 
acter as resistance on so simple a basis as that stated by Biffen. 
Having in mind these questions concerning the-nature and inheri¬ 
tance of wilt resistance in flax, the writer undertook the present investi¬ 
gations with the Departments of Plant Pathology and Experimental 
Breeding at the University of Wisconsin in February, 1915, his objects 
being (1) to study the mode of penetration of flax plants by F. Uni , (2) to 
make comparative studies on the penetration of cabbage seedlings by 
F. conglutinans (3) to determine whether or not FJini enters the resistant 
flax plant, (4) to study the relation of the fungus to the tissues of suscepti¬ 
ble and resistant flax plants, and (5) to study the inheritance of wilt resist¬ 
ance through hybridization. Flax was found to be a most suitable 
plant for the hybridization work for a number of reasons—namely, it 
has a short growing season, can be grown to maturity in the greenhouse, 
is easily cross-pollinated, and highly resistant and susceptible strains 
are available. Even with these advantages it was not expected that 
more than a clue as to the nature of the inheritance of wilt resistance 
might be obtained in the time allotted for the work, since breeding is a 
slow process and it was necessary to develop methods as the work pro¬ 
gressed. 
NATURE OF WILT RESISTANCE 
MODE OF PENETRATION 
Before making a detailed study of the relation of the fungus to the 
various host tissues it was considered of fundamental importance to 
know how it enters the host, and to know whether or not it penetrates 
the resistant plant. There seems to be very little definite information 
as to the exact mode of entrance of the parasitic soil fungi into their 
hosts. It was hoped that by using pure-culture methods penetrations 
of flax and cabbage seedlings by species of Fusarium might be obtained 
so that they could be detected by aid of the microscope. Bolley (4) states 
that F. Uni penetrates the young flax plants at any point, through the 
seed, leaves, stem, or roots. His illustration shows very clearly that 
the fungus is able to penetrate the cell walls at any point, but he does 
not show conclusively the initial points of entrance. However, he was 
dealing with the subject mainly from a practical rather than from a 
standpoint of detailed microscopical study. 
