676 THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 



sort of cortex around the central spore which germinates as in Tilletia. Urocystis 

 Violce is common on the leaf -stalks and blades of Violets. 

 About 100 species of Tilletiacete have been distinguished. 



Sub-class III. — Mycomtcbtes. 



Mycelium many-celled. Reproduction asexual, either by spores of limited num- 

 ber in asci, or by conidia of limited number on basidia. 



Alliance XVIII. — Ascomycetes. 



Parasitic (or saprophytic) Fungi, producing spores in special tubular sporangia, 

 the asci. These spores, termed ascospores, do not exceed 8 in number. In addition 

 to the asci there are subordinate conidial fructifications. 



Families: ExoascaceoB, Perispariacece, Pyrenomycetes, Biscomycetes. 



As stated, this alliance is characterized by the possession of sporangial fructifi- 

 cations, consisting of tubular asci containing as a rule 8 ascospores. A number of 

 such asci are shown in fig. 388 - with sterile supporting hyphse, the paraphyses, 

 between them. In addition to these ordinary and typical ascus-bearing fructifi- 

 cations, secondary fructifications producing conidia or chlamydospores are largely 

 met with; consequently many of these Fungi appear under several forms in addition 

 to the ascus stage. The Ascomycetes are divided into families according to the 

 characters of the ascus-fruit. In tlie Exoascacece the asci are borne freely and 

 exposed on the mycelium; in the other three families in special receptacles. In the 

 Perisporiaceoe the group of asci is contained in a nut-like or tuber-like body; in 

 the Pyrenoviycetes the asci are produced in special pear-shaped excavations in a 

 solid tissue which open by a pore to the exterior; in the DiscoTtiycetes the receptacle 

 forms an open plate or cup, or sometimes an irregular body covered with the layer 

 of asci. 



Exoascacece. — This family comprises the parasitic genera Exoascus and Taph- 

 rina, the gall-like deformations caused by which were so fully described on pp. 524 

 and 527. The tissues of the host-plants are penetrated by the mycelia of these 

 forms, and the asci are produced over the surface of the parts attacked, generally 

 bursting thi-ough the cuticle of the epidermis. Each ascus contains 8 spores, but in 

 many species many more than this number are often found; this is due to the fact 

 that the 8 original ascospores begin to bud whilst still within the ascus, producing 

 a large number of secondary spores (conidia). Exoascus has a perennial mj-celium, 

 and to its species are due a large number of the " witches'-brooms " and other 

 hypertrophies. E. Pruni produces the " pocket-plum " (c/. p. 524); E. Alni-incance 

 the curiously altered Alder catkins represented in fig. 358 ' (p. 523); E. Carpini the 

 birds'-nest-like witches'-brooms of the Hornbeam; E. defoi-mans the "curl" of 

 Peach-leaves. Tajyhrina is largely a leaf-parasite, and its mycelium is not peren- 

 nial. T. carnea causes blisters on the leaves of the Birch. 



