74 MASSACHUSETTS HORTICULTURAL SOCIETY 



paid the salary and expenses of many scientific workers whose 

 efforts if apphed at the right time, could probably have prevented 

 the spread of such an epidemic as that which we are now consider- 

 ing. I have no hesitation in saying that if the chestnut bark 

 disease had originated in a national forest where there was a co- 

 ' operating pathologist, it would have been put out like a forest fire, 

 as a matter of routine, before it became extensive enough to be 

 dangerous. 



Cause and Symptoms. 



The chestnut bark disease is caused by a fungus parasite known 

 variously as Diaporthe ixirasitica Murrill, or Valsonectria para- 

 sitica (Murr.) Rehm. It is also considered by some investiga- 

 tors to belong to the genus Endothia. In other w^ords, there is 

 disagreement among mycologists as to the name of this fungus. 

 For convenience, waiving the question of correctness, I will in this 

 lecture use Murrill's original name, although this name has not 

 been generally accepted by mycologists. 



When any spores of this fungus gain entrance into a wound on 

 any part of the trunk or limbs of a chestnut tree they com- 

 monly give rise to a concentrically spreading lesion, which soon 

 girdles the tree. If the part attacked happens to be the trunk, 

 the whole tree in consequence is killed, sometimes in a single 

 season. If the smaller branches are attacked, only those portions 

 beyond the point of attack are killed, and the remainder of the 

 tree may survive for several years. 



Some of the symptoms are quite prominent. Limbs with smooth 

 bark attacked by the fungus soon show dead, somewhat discolored, 

 sunken areas (occasionally with a raised margin), which continue 

 to enlarge and soon become covered more or less thickly with 

 yellow, orange, or reddish-brown spots about the size of a pinhead. 

 These spots are the pustules of the fruiting fungus. Following a 

 rain, or in damp situations, masses of summer spores are commonly 

 extruded in the form of long, irregularly twisted strings or "horns," 

 which are at first bright yellow to greenish yellow, or even buff, 

 becoming darker with age. If the lesion is on the trunk or a 

 large limb with very thick bark there is no obvious change in 



