Plant Diseases 
337 
Not only do Apple trees suffer from this disease, but 
the Beech, Oak, Hazel, Ash, Hornbeam, Maple, and 
Bird-cherry are all said to be subject to its ravages. 
Therefore it is most difficult to keep trees free from the 
disease, unless care is taken to prevent them being 
wounded in any way. 
APPLE SCAB 
This is another dreaded disease of the Apple, which 
does considerable damage both to fruit and tree alike. 
The mycelium of the disease creates most of its damage 
in the superficial tissue of the leaves and fruit, forming 
dark-brown or black spots where the tissue is destroyed. 
When matured, the cuticle of the leaf or fruit is ruptured, 
and great numbers of very minute branches grow out 
into the atmosphere, each one producing a spore or 
conidium at its apex. When these conidia are matured 
they drop off and germinate, producing a little hypha, 
which makes its way into the tissue of the leaf or fruit, 
there to develop into the disease again. 
The minute conidia (or spores) may be blown about by 
the wind, or they may be carried by insects or on the feet 
of birds, &c. The disease is perpetuated during the winter 
by the resting mycelium, which springs into active growth 
when the warm weather returns in spring and the young 
leaves burst out of the bud. 
When badly infected, the trees themselves suffer as well 
as the fruit, as the leaves are partially destroyed, and it is 
by the leaves that the food of the whole tree is manu- 
factured. The diseased leaves and fruit should be carefully 
( C 525 ) 23 
