464 A TEXTBOOK OF BOTANY [Ch. X 



basidiospores, formed on basidia, which are specialized ends 

 of hyphse arranged more or less definitely in a hymenium. 

 As noted already (page 449), the basidium is probably the 

 morphological equivalent of the ascus (an everted ascus), 

 and was formed originally after a fertilization which is now 

 lost. The Basidiomycetes include more species than the 

 Ascomycetes, — over 18,000. There is little doubt that 

 they have been evolved from the Ascomycetes, though at' a 

 very remote period. 



The Basidiomycetes include some four principal orders 

 as follows : 



Order 1. Ustilaginales: the Smuts. 



Order 2. Uredinales: the Rusts. 



OrderS. Hymenomycetes: the Toadstool Fungi. 



Order J^. Gasteromycetes : the Puffballs. 



Order 1. Ustilaginales: the Smuts. These are par- 

 asites causing destructive diseases chiefly in members of the 

 Grass family, and especially in the cultivated cereals, the 

 grains of which they fill with a powdery black mass of spores, 

 — whence their name. Some 2200 species are known. 



A common and destructive form is the Corn Smut (Fig. 

 324). When the spores reach a young Corn plant, they form 

 mycelia which penetrate limited areas of any part of the 

 plant, but develop especially in the stamens or the ovaries, 

 which become greatly swollen. Inside these parts, the 

 mycelium abstricts great numbers of thick-walled, dark 

 colored resting spores, the " brand spores,' ' which are the 

 smut. These spores are disseminated by wind, rest over 

 winter in the ground, and in spring germinate to a short 

 mycelium (pkomycelium) which lives saprophytically in 

 organic material, for which reason the presence of manure 

 greatly promotes the development of the disease. The cells 

 of this mycelium give rise by budding to spores which are 

 morphologically basidiospores despite their indefinite num- 

 ber ; and moreover they increase still more by budding, much 

 after the manner of the Yeasts. They infect Corn seed placed 



