Plant Diseases 
O A ^ 
o4o 
precautions should be taken to guard against it getting 
a hold of the bushes. 
The leaves and young shoots become covered with a 
delicate white mycelium, the hyphae of which penetrate 
into the tissue of the leaves or shoots, and live on the 
contents of the cells. If it is a bad attack, the leaves 
and shoots become covered with a felty substance, the 
hyphae being inter- 
woven into practic- 
ally a solid mass. On 
this mycelium great 
numbers of conidia 
are formed, which 
may be scattered by 
the wind, &c., and 
wherever one alights 
under favourable con- 
ditions it will crermi- 
O 
nate, produce a short 
hypha, and, later, a 
close felty mass of 
mycelium and conidia 
again. 
Most people who 
grow Roses are familiar with this disease, how the leaves 
curl up and drop prematurely, when practically all the 
nourishment of the cells has been devoured and the tissue 
destroyed. 
As the season advances, another kind of fruit is pro- 
duced in perithecia, which are sunk in the mass of my- 
celium. In these perithecia, asci containing ascospores 
i, Summer form of fruit on rose leaf (nat. size). 2, 
Chains of spores (magnified 250). 3, Single spore 
germinating (magnified). 
