FUNGI AND FUNGOUS DISEASES OF PLANTS 261 



CLASS III. FUNGI 



SUB-CLASS I. PHYCOMYCETES (the algae-fungi). Leading genera 

 used as illustrations Rhizopus (bread mold), Plaxmopara 

 (grape downy mildew), Phytophlhora (potato blight) 



SUB-CLASS II. ASCOMYCETKS (the sac fungi). Leading genera 

 used as illustrations Sclerotinia (brown rot), Mincrwtphaera 

 (lilac mildew), Morchella (morel), Penicillium (blue mold), 

 Saccharomyces (yeast) 



SUB-CLASS III. LICHENS. Leading genera used as illustrations 

 Parmelia, Usnea (bearded moss), Cladonia 



SUB-CLASS IV. BASIDIOMYCETES (the basidium fungi). Leading 

 genera used as illustrations Ustilayo (smut), Puccinia (rust), 

 Coprinus and Polyporus (mushrooms), Lycoperdon (puffball) 



PROBLEMS 



1. Why does bread " mold " ? How can it be prevented from doing so? 



2. Why is it that a plant disease newly introduced into a country 

 seems to spread more rapidly and to prove more destructive than 

 diseases that have long been in that country? 



3. Can you account for the fact that lilac bushes seem to be fairly 

 thrifty even though they are infested with lilac mildew? 



4. Why are lichens sometimes called "the advance guard of vege- 

 tation " ? 



5. If you can secure the data from published reports, or can perform 

 an experiment for the purpose, determine the difference in yield that 

 may be made by selecting or treating seed oats or corn so as to remove 

 the smut disease. What percentage of gain on the crop may be made 

 in this way? 



6. Under what circumstances may fungi that are parasitic upon 

 plants or animals be of service to the farmer or gardener? 



7. Why are railroad ties and other timbers often treated with poison- 

 ous solutions before they are used ? 



8. Discover from first-hand study or from publications the life history 

 of some of the worst fungous parasites of your locality. 



