1914] 
COOLEY—SCLEROTINIA CINEREA 293 
De Bary (4), in 1886, gives us the first important contribu- 
tion to our knowledge concerning the action of parasites on host 
cells. This author, in his epoch-making research on the fungus 
now known as Sclerotinia libertiana, reports that the organism 
secretes a substance that discolors, plasmolyzes, and finally 
kills the host cells. This toxic secretion penetrates the host 
cells in advance of the fungus, killing them before they are 
actually pierced by the fungous filaments. De Bary was able 
to isolate this toxic substance, which he considered as probably 
an enzyme, and found that it would cause an injury to the 
host tissue similar to that produced by an attack of the fungus 
itself. He holds that the fungus will not grow on living tissues, 
for it attacks only through a wound and kills the cells in ad- 
vance of itself, thus not actually growing upon the living tissue. 
The product resulting from the disintegration of the cell wall 
of the host was thought to be a sugar that served as food for 
the fungus. In this connection de Bary also mentions finding 
oxalic acid encrusting the older fungous filaments. / 
Тһе next important paper on the interaction of host and Е 
parasite was that of Marshall Ward (51) published just two years 
after de Bary's work and concerning itself with a species of pd 
Botrytis causing a lily disease. In this excellent piece of work | 
the author showed that the fungous hyphae on coming in 
contact with such solid substances as sections of a lily bulb, or 
even a cover glass, secrete from the tips drops of a substance that а: 
has a very peculiar effect on the host cell. He 
ound аба 
water extract of this secretion when applied to sections of а 
lily bulb will cause the cell walls to swell and to assume an ab- аз 
normal appearance; the middle lamella is first dissolved and 
finally the entire cell wall is disorganized. Ward does not con- 
sider that this toxic secretion is stimulated by starvation. 
Several investigators have held that the penetration of 
many fungi is due to chemotropism, i. e., that penetration of 
the fungous hyphae is due to some stimulus which the constit- 
uents diffusing slowly from within the host cells exert. Biisgen 
(16), Miyoshi (89), Behrens (6), Schmidt (44), and others have 
adhered to the view that chemotropism is important, but more 
recent work, such as that of Fulton (25), does not uphold the 
theory. 
