180 



BOTANY 



twigs, etc., where their bright orange-yellow or amber-colored gela- 

 tinous fruit-bodies are conspicuous. 



SUBCLASS III. AUTOBASIDIOMYCETES 



The greater number of the more familiar larger Fungi belong to 

 the Autobasidiomycetes, of which the Toadstools and Puffballs are 

 the types. The lowest members of the group do not form a definite 

 fruiting-body, but in most of them this is large and of very charac- 

 teristic form. 



Order I. Exobasidiineae 



B 



FIG. 146. Exobasidium Vaccinii. A, 

 flower of Menziesia, hypertrophied 

 by Exobasidium. (Natural size.) B, 

 basidia and spores ( X 525) . (B, after 

 WORONIN.) 



Among the simplest members of the 

 Autobasidiomycetes, are the Exobasi- 

 diinese, represented by the genus Exo- 

 basidium. E. Vaccinii (Fig. 146) is 

 widespread throughout northern re- 

 gions, where it attacks Cranberry, 

 Huckleberry, and related forms. The 

 plant is strictly parasitic, growing 

 within the intercellular spaces of the 

 host, upon which it causes extraor- 

 dinary gall-like deformations of the 

 leaves and flowers. These diseased 

 parts are sometimes entirely destitute 

 of cholorophyll and present a pink or 

 white color. 



The spores are borne upon basidia of 

 typical form, which are developed from 

 the ends of the mycelial filaments which 

 break through the epidermis of the host. 



Order II. Hymenomycetineae 



The Hymenomycetinese comprise more than ten thousand species, 

 the largest order of the Fungi, and exhibit great variety in the 

 character of both the mycelium and the fruiting parts. 



Mycelium. The mycelium always consists of septate hyphse, 

 which may be loose and delicate in texture, but more commonly 

 are compacted into rootlike strands, or sometimes hard masses or 

 sclerotia. In some species growing in decaying wood, the mycelium 

 grows between the layers of wood, and develops continuous leathery 

 or papery layers of great extent. In such forms as the common 

 Mushroom, the mycelium spreads widely through the substratum, 

 which it binds together, so that large masses may be taken out, 

 which consist in large part of the mycelium. This constitutes the 

 " spawn" of the Mushroom which is used for propagation. 



