4 FARMERS’ BULLETIN 2068 
damage. The fungus sometimes 
grows on dead chestnut oak, red 
maple, shagbark hickory, and stag- 
horn sumac. In Europe, it has at- 
tacked three of the native oak 
species. 
THE BLIGHT FUNGUS 
The blight fungus grows mainly 
in the bark of chestnut trees, form- 
ing masses of flattened threadlike 
strands, called mycelia. Mycelial 
strands feed upon and kill the bark 
tissues. They advance through the 
bark much as plant roots advance 
Ficure 3.—Mycelial fans of the chestnut 
blight fungus, revealed by scraping 
away the outer bark from part of a 
ecankered chestnut stem. 
through the soil, and form buff-col- 
ored mats or fans in the bark and 
cambium (fig. 3). The fungus 
continues to grow around chestnut 
trunks or limbs until it encircles 
them. The affected parts then die. 
The fungus forms fruiting bod- 
ies, or blisters, in and on dying and 
dead bark. These blisters look like 
yellow, orange, or red-brown pin- 
heads dotted over the surface of the 
cankers (fig. 4). They bear micro- 
scopic spores, which correspond to 
the seeds of higher plants. Spores 
of one type, called pycnidiospores, 
are produced within some of the 
blisters in great numbers. In damp 
weather they are forced out in 
slender sticky ribbons, much as 
paste is squeezed froma tube. They 
then form tiny yellowish or orange- 
colored hairlike tendrils, called 
spore horns (fig. 5). Spores of this 
type, being sticky, adhere to insects, 
birds, and other animals and thus 
may be carried for long distances. 
Rain washes them into wormholes 
and wounds in tree stems and 
branches, where new infections may 
develop. 
Blisters producing spores of a 
second type, called ascospores, are 
made up of flask-shaped structures 
with very small openings. These 
spores do not form spore horns. 
They are borne within the flasks in 
groups of eight, each group en- 
closed in a thin, transparent. sac. 
Under favorable conditions of mois- 
ture and temperature, the sacs push 
up through the neck of the flask and 
burst, throwing the spores into the 
air. Thus freed, the spores are car- 
nied by air currents, often for great 
clistances. 
