678 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 



able to remain dormant over long periods. Aspergillus i.s sometimes paraf?itic, 

 and is stated to promote a diseased condition of animal tissues known as mycosis. 

 A. fumigat.us is found growing spontaneously in the air-passages of birds and in 

 the human lungs. 



Tiiheraceoi. — These are subterranean saprophytes whose mycelia grow in humus. 

 Their fructifications are solid, tuber-like bodies of various sizes. The Truffles 

 {Tuber rufum, T. inelanosporum,, T. cestivtmi, &c.) ai-e well-known, and several of 

 the species are esteemed as delicacies. In section the Truffle-fruit shows a curious 

 mottled appearance due to its irregular chambered character. The chambei's are 

 filled with hyphse which produce numerous oval asci, each containing 4 spores 

 (c/. fig. 387 \ which represents an enlarged chamber); the spores are covered with 

 delicate spines. The wall of the fructification consists of a hard parenchyma-like 

 layer, and possesses a rough and warted exterior. As the fructification ripens the 

 mycelium disappears, the Truffles being found detached in the soil. The spores are 

 ultimately liberated by the decay of the fruit. Elaphomyces produces fruits about 

 the size of a nut. The mycelium of species of this genus is concerned in the for- 

 mation of the fungal investment or mantle of the roots of Pine-trees known as 

 mycorhiza (c/. vol. i. pp. 249, 250); in the Amentacese, &c., neither the species nor 

 group to which the Fungi forming this mantle belong has been ascertained. 



Pyrenomycetes. — An extremely large and varied group, including both parasitic 

 and saprophytic forms. The essential character of the family is the presence of 

 flask-shaped chambers with a pore at the apex in which the asci are produced. 

 The chambers, the perithecia, may be either solitary upon the mycelium in the 

 simpler forms or embedded in receptacles of most varied form (the stromata) in the 

 more complex. Sections of perithecia are shown in figs. 385 * and 386 °. A great 

 many Pyrenomycetes possess conidial as well as ascus - fructifications. The conidia 

 may arise in tufts from the surface of the mycelium or in urn-shaped cavities — not 

 unlike perithecia — which have been termed pycnidia. As a rule, the conidial pre- 

 cedes the afäcal stage. This variety in fruiting has led to the recognition of several 

 forms, which are only stages in the life-history of one Fungus. Consequently, as 

 knowledge extends, many of these supposed species have to be suppressed. 



Among the simpler forms may be mentioned Podospora, which produces solitary 

 sessile perithecia upon its mycelium. Polystigma rubrum, which occurs on the 

 leaves of species of Cherry and Plum, produces a brilliant red spotting on the leaves. 

 The mycelium permeates the internal tissues, and during the summer the conidial 

 i-eceptacles or pycnidia are formed. Later, usually in the following spring, in the 

 fallen leaves, the perithecia arise, and the ascospores now liberated infect the young 

 foliage in the vicinity. Nectria cinnabarina, another fairly simple form, occurs as 

 little red cushions on the branches of Horse-Chestnut, Elm, Sycamore, &c.; these 

 cushions burst through the bark budding oft' conidia (this is the bright red stage), 

 whilst later, as tiny lobes, the perithecia arise upon them, each lobe containing a 

 single perithecium (this is the dull crimson stage). The number of simple parasitic 

 Pyrenomycetes is almost endless. 



