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 Perisporiacci, 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 JUlvellacei, 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 Sphceriacei, 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. Each of these four orders must be 



* Leveille, J. H., "Organisation, &c., de 1'^lrysiphe," in "Ann. des Sci. 

 Nat." (18,51), xv. p. 109. 



