THALLOPHYTES— FUNGI 



283 



species are destniotive parasites and are of the very greatest 

 importance in agriculture. 



The Basidiowiycetes 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-hasidiomycetes with a four- 

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

 basidiocycetes with a one-celled basidium bearing four spores. 



Fig. 133. — Wheat rust; (a) cross-section showing the secial stage on the .barberry; (6) 

 urediniospore ; (c) teliospore: (d), germinating ' tehospore showing sporidia; (e) pycnidia. 



The Profo-hasidiomycetes is divided into the Usitila-ginales 

 or smuts and the Uredinales or rusts. 



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

 characterized by the com smut, TJstila-go maydis. The mycelium 

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

 growths, which may ap'pear 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 gi-ain 

 every year. 



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



