CHAPTER THIRTY-NINE 



FUNGI 



Or the plants without chlorophyll the most conspicuous are 

 the fungi. They form an exceedingly large and diversified group, 

 ranging in size from microscopic one-celled forms almost as small 

 as the larger bacteria to the large, fleshy mushrooms and to the 

 massive bracket fungi found on tree trunks and logs, which 

 may weigh 20 or 30 pounds. Among the most important fungi 

 are the yeasts, molds, mildews, smuts, rusts, and mushrooms. 



All the fungi derive their food either from living plants, 

 from animals, or from dead plant and animal tissues and their 

 products. The yeasts, molds, and most of the mushrooms are 

 saprophytes. These and their bacterial associates are the chief 

 agents of fermentation and decay. The smuts, rusts, and some 

 of the mildews are parasites on the seed plants. They produce 

 injurious effects (diseases) on the host plant, which result in 

 serious losses to the farmer and gardener and in reducing the 

 supply of plant products for every one. 



Some of the mushrooms are edible and furnish small quantities 

 of pleasantly flavored food for man and animals ; some of the 

 fungi found on roots undoubtedly aid in the nutrition of the plant 

 on which they grow ; and others produce diseases among annoy- 

 ing insects and help to destroy or keep them in check. 



The vegetative body of a fungus. The vegetative bodies of 

 most fungi are composed of branching filaments called hyphce 

 (singular, hypha). In the molds and mildews these fine threads 

 are readily visible with a magnifier, and under favorable condi- 

 tions for growth form a soft, cottony layer in or on the substrate 

 where the fungus is growing. The whole mass of hyphae which 

 make up the vegetative body of a fungus is called a mycelium. 

 Sometimes the hyphae, as in the yeasts, are very short ; they are 

 composed of cells that separate readily, and the filaments are 

 rarely composed of more than a few cells. In the fleshy fungi 



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