Plant Diseases 335 
piac.e even when we have cut an infected branch well 
back. 
During: the autumn little white cushions are formed 
at the points where the mycelium or disease plant seems 
to be strongest, eating away the tissue of the tree. These 
little cushions pro- 
duce very tiny spores 
on their surface, 
which, when they are 
matured, germinate 
at once, extending 
the disease; or they 
may be carried by 
the wind some dis- 
tance — being very 
small and light — or 
by insects, or on the 
feet of birds, &c. 
Wherever a spore 
alights on a wounded 
part of the tree it 
at once germinates, 
forming a small 
hypha which gradually develops into the mycelium or 
disease plant. Then, in the spring, if those parts where 
the disease has broken through the bark are examined 
carefully, little red points will be seen here and there. If 
one of these is taken off, together with a piece of the bark, 
placed between two pieces of pith, and sliced with a razor, 
and the extremely thin slices examined under first the low, 
and afterwards the high, power of the microscope, they 
Apple-tree Canker. Branches of an apple tree showing 
the bark destroyed by the fungus 
