76 FUNGI. 
peridium is filled with branched threads, which produce asci of a 
very evanescent character, leaving the pulverulent sporidia to 
fill the central cavity. The species are all small, and singular for 
their habit of affecting animal substances, otherwise they are 
of little importance. The Perisporiacei, on the other hand, are 
very destructive of vegetation, being produced, in the majority 
of cases, on the green parts of growing plants. To this order 
the hop mildew, rose mildew, and pea mildew belong. The 
mycelium is often very much developed, and in the case of the 
maple, pea, hop, and some others, it covers the parts attacked 
with a thick white coating, so that from a distance the leaves 
appear to have been whitewashed. Seated on the mycelium, at 
the first as little orange points, are the perithecia, which enlarge 
and become nearly black. In some species, very elegant whitish 
appendages radiate from the sides of the perithecia, the varia- 
tions in which aid in the discrimination of species. The perithecia 
contain pear-shaped asci, which spring from the base and enclose 
a definite number of sporidia.* ‘The asci themselves are soon 
dissolved. Simultaneously with the development of sporidia, 
other reproductive bodies are produced direct from the mycelium, 
and in some species as many as five different kinds of reproduc- 
tive bodies have been traced. The features to be remembered in 
Perisporiacei, as forming the basis of their classification, are, that 
the asci are saccate, springing from the base of the perithecia, 
and are soon absorbed. Also that the perithecia themselves are 
not perforated at the apex. 
The four remaining orders, though large, can be easily charac- 
terized. In Tuberacei, all the species are subterranean, and the 
hymenium is mostly sinuated. In Elvellacei, the substance is 
more or less fleshy, and the hymenium is exposed. In Phaci- 
diacei, the substance is hard or leathery, and the hymenium is 
soon exposed. And in Spheriacei, although the substance is 
variable, the hymenium is never exposed, being enclosed in 
perithecia with a distinct opening at the apex, through which 
the mature spores escape. Tach of these four orders must be 
* Léveillé, J. H., ‘Organisation, &., de YErysiphé,” in “Ann. des Sci. 
Nat.” (1851), xv. p. 109. 
