THALLOPHYTES FUNGI 



283 



species are destructive parasites and are of the very greatest 

 importance in agriculture. 



The Basidiomycetes include the smuts and rusts which 

 are microfungi and also the large fleshy fungi of which the mush- 

 rooms and puffballs are types. 



They are divided into the Proto-basidiomycetes with a four- 

 celled basidium, each bearing a one-celled spore, and the Auto- 

 basidiocycetes with a one-celled basidium bearing four spores. 



FIQ. 133. Wheat rust; (a) cross-section showing the secial stage on the barberry; (b) 

 urediniospore; (c) teliospore; (rf) germinating teliospore showing sporidia; (e) pycnidia. 



The Proto-basidiomycetes is divided into the Usitilaginales 

 or smuts and the Uredinales or rusts7 



The smuts (Fig. 132) attack many plants, but may be 

 characterized by the corn smut, Ustilago maydis. The mycelium 

 works within the host and fmally causes swollen, tumor-like 

 growths, which may appear on any part of the plant. When 

 mature, these masses are filled with spores which germinate the 

 following spring, producing short filaments. Each filament pro- 

 duces spores which are capable of infecting young plants. The 

 smuts are very destructive to many of our cultivated plants. 

 The grain smuts are among the most important causes of plant 

 diseases and destroy many millions of dollars' worth of grain 

 every year. 



The rusts (Fig. 133) may be illustrated by the wheat rust, 



