FUNGI. 415 
and plums, producing very rapid decay. These 
patches are caused by Ozdium fructigenum, which, 
when it has once obtained possession of a tree, 
spreads with fatal rapidity, destroying the fruit 
while still hanging on the branches. The d/anc 
de roster or rose-blight, which gives a melancholy 
leprous appearance to the leaves and calyces of 
roses, used to be called Odium leucoconium ; 
but this stage was only an incomplete or coni- 
diferous condition of Spherotheca pannosa. An 
allied species constitutes the hop-mildew, which 
has often proved so disastrous in the hop-gardens 
of Kent, and raged as an epidemic in 1854. 
All the mildews and blights hitherto described 
are light-coloured; but there is another class of 
fungi, equally destructive, called black mildews. 
They are caused principally by species of Anten- 
naria and allied genera, which form thick, black, 
felt-like patches on leaves, disfiguring trees, and 
injuring them fatally, by closing up their pores, 
and preventing the free admission of the air; and 
also by depriving them of the full, direct light of 
the sun. They are principally developed on those 
leaves which had previously been covered with 
the honey-dew of aphides or plant-lice. Whole 
plantations are often literally covered with sack- 
cloth and ashes. In the Azores the orange-groves 
of St. Michael have suffered dreadfully from this 
