FUNGI. 305 
sowing their spores on rice paste or on any suit- 
able preparation. The disease of the silkworm 
and several other epizoic fungi are also readily 
propagated by inoculation; while the common 
bunt may be communicated artificially to grains 
of wheat by rubbing them with the dark powder ; 
and the rust of the garden rose may be made to 
infect healthy leaves by watering the ground 
around the bush with a decoction of diseased 
leaves. 
Fungi afford a remarkable illustration of the 
fact almost universally observed, that agencies 
which are generally beneficial sometimes prove | 
destructive. While performing their office as 
the scavengers of nature, these plants some- 
times carry their operations too far, and by their 
rapid increase, and their devastating effects on the 
fruits of the earth, cause incalculable damage. 
Some of the most destructive diseases of the 
cereal crops are caused by the ravages of micro- 
scopic fungi, which attack respectively the flower, 
the grain, the leaves, the chaff, and the straw. 
Those who have seen corn fields in July, when the 
flower is bursting through the sheath, must have 
often noticed several greyish-black heads appear- 
ing here and there among the verdant stalks. In 
some fields these are few and far between; in 
others they are more numerous, almost every 
