Dec. io, 1917 
Flaxwilt 
581 
growth of the fungus and which increases the transpiration of the plant. 
This seems reasonable, so far as it goes, but does not seem sufficient for 
a complete explanation. If it were a case of the water supply being 
cut off by the clogging of the vessels, we should not expect so much of 
the one-sided wilting of plants which is so common with flax. The 
leaves on one side of the stem may become yellow, while those on the 
other side remain perfectly normal. Stems of plants which are wilted 
on one side only become characteristically twisted or curved, owing per¬ 
haps to unequal growth and shrinkage of tissues. If this wilting were 
due to the mere cutting off of the water supply at some point, it would 
be reasonable to except that when a normal plant has its stem cut half- 
through it would turn yellow and wilt on the cut side. Five flax plants 
were cut in this way, but none of them showed any yellowing or wilt¬ 
ing from the wound. It is certain that by the time the foliage of the 
plant begins to wilt the root system has been invaded rather severely 
Fig. 6 .—longitudinal section of the woody tissue of the susceptible flax plant showing the invading 
hyphse of Fusarium Uni. Notice the microspores of the fungus in the host cells. 
by the fungus, and the root hairs are largely destroyed. This is espe¬ 
cially true in case of the flax, and would likely account to a considerable 
extent for any lack in the water supply, and for the general weakening of 
the plant. Furthermore, there must be a protoplasmic disturbance in 
cells of the invaded tissues, which helps to produce the local symptoms. 
Phenonema of this kind might be due to toxic substances produced by the 
fungus, which interferes with the normal functions of the host proto¬ 
plasm. The fungus also consumes a part of the food, and water sup¬ 
ply of the plant. There are very likely, a number of factors which aid 
in the production of wilt symptoms due to the invasion of flax by F. Uni — 
namely (1) Partial destruction of the root system which limits the food 
and water supply of the plant; (2) use of part of the food and water 
supply of the plant by the fungus; (3) an increase in transpiration and 
an increase in the growth of the fungus due to a rise in temperatures; 
and (4) the possible production of toxic substances by the fungus, which 
interferes with the normal functions of the host protoplasm. 
