ENDOTHIA CANKER oF CHESTNUT 563 
only occasionally have anything like oil globules or vacuoles been seen. 
Each cell of a spore contains two to four nuclei. Like the conidia, the 
ascospores have a sticky coating on the outside. 
Mycelium 
The individual hyphe are branched, septate threads, the branching 
being always monopodial, and usually not more than one branch is 
-produced from a single cell. The hyphz are not of uniform diameter, 
but vary from 1.5 to 12 wu, and the cells vary from 20 to 50 uw in length. 
Each cell contains several small nuclei. On most culture media the 
mycelium becomes yellow after a few days, due to the production of a 
pigment. The pigment is soluble in alcohol and alkalies, and insoluble 
in acids. In alkaline solutions the pigment becomes purple. It is a 
chemical compound belonging to the group known as aurines. 
A character of this species which distinguishes it from all other related 
fungi is the presence in the diseased bark and in the cambium of 
fan-like mats of mycelium (Plate XXXIX). Each mat consists of a 
number of bundles of parallel hyphe diverging from a single point like 
the rays of a fan. They are flat because they have to squeeze between 
the bast-fiber zones. The edges of the fans are fairly regular and are 
surrounded by a darker gelatinous band of disintegrating host cells. The 
fans vary in length from a millimeter to two or three centimeters. The 
young ones on the advancing edge are pure white, but the older ones become 
light yellow or buff. The hyphz composing each ray branch only sparsely, 
and are more uniform in diameter than those in agar culture. They do 
not anastomose in any way. 
Pathogenicity 
On Castanea dentata 
Murrill (1906 a) proved that Endothia parasitica is pathogenic on the 
American chestnut. This fact is so easy of demonstration that it has 
never been questioned since that time. Constant association of the fungus 
with the canker is readily noticed by all investigators. The fungus has 
been isolated and grown in pure cultures by a number of pathologists. 
Inoculations from pure cultures and the production of typical cankers are 
reported first by Murrill and later by various others. The writers of this 
bulletin have separately carried out Koch’s four rules of proof many times, 
in New York and Pennsylvania. 
On other spectes of Castanea 
Metcalf (1908 a), after having failed to produce the disease by inocula- 
tions on Japanese chestnuts in the field, states that this variety is immune. 
