PEAR DISEASES 343 
by brown depressed scars. In the late spring dark-brown, 
wedge-shaped horns, which later become yellowish, are devel- 
oped. 
Cause. 
The eastern pear rust is caused by the fungus Gymnospo- 
rangium globosum. Like other rust fungi it has two distinct 
host plants, the 
pear and the red 
cedar. If the spots 
of an affected pear 
leaf be examined, 
the upper surface 
will show small 
black fruiting 
bodies known as 
pyenia. These do 
not function in the 
life-history of the 
pathogene so far as 
is known, but are 
mentioned for their 
diagnostic value. 
They are found in 
the early summer. 
Shortly after their Fie. 94. — Eastern rust on pear-fruits. 
appearance another 
type of fruiting body develops on the lower surface opposite 
the pyenia. These structures are known as ecia. Occasion- 
ally they are found on the upper side of a leaf and even on the 
petioles. Ordinarily they are grouped irregularly over the 
affected area, although sometimes they are arranged in two 
rows, one on either side of the midrib. cia may also develop 
on the apple, hawthorn and mountain-ash. These bodies are 
deep cup-shaped, with their walls split part way to the base, 
