Dec. io, 1917 
Flaxwilt 
587 
the protoplasm of the resistant plant may naturally contain a substance 
or substances injurious to the fungus. We know that the resistant plant 
differs^from the susceptible plant in respect to its physiological nature. 
This difference might be due to some permanent chemical composition 
of the protoplasm as suggested above, or it might possibly be due to a 
hypersensitiveness of the protoplasm of the resistant plant which causes 
it to react much more readily than does the protoplasm of the suscepti¬ 
ble plant in producing the phenomena which cause resistance. The 
fungus seems to be less vigorous in the invaded cells of the resistant plant 
.than in the invaded cells of the susceptible plant; in other words, it is 
less abundant in the cells of the resistant plant. It seems possible, 
therefore, that some toxic or other chemical substance is produced by 
the protoplasm of the host which has a deleterious effect on the fungus. 
The coarse, granular appearance and staining reaction of the protoplasm 
of the invaded cells indicate that considerable change has taken place. 
Apparently this change is accompanied by an injury to both the host 
cells and the fungus hyphae. Perhaps some substance is produced by 
the host protoplasm during the change which has an injurious effect on 
the fungus. When the hyphae of the fungus come in contact with the 
modified or corky walls of the cells they fail to penetrate, and further 
invasion is prevented. Possibly these thickened walls would not be 
sufficient within themselves to prevent invasion, but they serve as a 
barrier to the fungus after it has been weakened by protoplasmic reaction 
on the part of the invaded host cells. These phenomena seem to indi¬ 
cate that resistance is due either directly or indirectly to the chemical 
nature of the host protoplasm. Appel (1) believes resistance in plants 
to be of a chemical nature and makes the following statement: 
Efforts must be made to find the causes of immunity, and after solving this question 
to determine without infection the disease-resistant qualities in different varieties 
and individuals in order to be able to establish the desired resistance and at the same 
time eliminate undesirable qualities. 
Such a theory might at first seem entirely feasible; but, when the* 
multiplicity of constitutional and environmental factors influencing the 
production of the resistant character is considered, it appears more im¬ 
probable that any such analysis will ever be satisfactorily made. Ward 
(25, 26) also speaks of the chemical nature of resistance. He ( 26 , p. 21) 
says: 
Infection, and resistance to infection, depend on the power of the Fungus-proto¬ 
plasm to overcome the resistance of the cells of the host by means of enzymes or toxins; 
and, reciprocally, on that of the protoplasm of the cells of the host to form anti-bodies 
which destroy such enzymes or toxins, or to excrete chemotactic substances which 
repel or attack the Fungus-protoplasm. 
This theory might be offered as a partial explanation for the resistance 
of F. Uni by flax plants. 
