CHAPTER I 

 THE STRUCTURE AND CLASSIFICATION OF THE FUNGI 



The molds, yeasts, and actinomycetes are Fungi, a subdivision of 

 the Thallophyta, one of the four divisions of the plant kingdom. A 

 division in botany corresponds to a phylum in zoology. The Thal- 

 lophytes are characterized by their growth in irregular plant masses 

 not differentiated into roots, stems, and leaves like higher plants. 

 Such a mass of plant tissue is called a thallus. The Thallophytes 

 comprise the Algae and the Fungi. The former, being provided with 

 chlorophyll, are capable of synthesizing their food from inorganic 

 compounds by the energy of sunlight; the latter, being devoid of 

 chlorophyll, must depend for their food upon organic matter syn- 

 thesized by other organisms, growing as either saprophytes or para- 

 sites. The lichens (Lichenes) have been considered a third subdivi- 

 sion of the Thallophytes, because they are peculiar plants composed 

 of algae and fungi growing together in symbiosis. Most modern 

 authors classify them with the Fungi. 



The fungi are subdivided into the true fungi or Eumycetes, the 

 bacteria or Schizomycetes, and the slime-molds or Myxomycetes. 

 The relationships of the last group are not clearly understood; in 

 fact some biologists believe that they should be classified with the 

 protozoa in the animal kingdom. The relationships of the bacteria 

 are also in some doubt, but the actinomycetes seem clearly to repre- 

 sent a transition between them and the molds. The molds and yeasts 

 belong to the Eumycetes. In this work where the word "fungi" is 

 used without qualification, it will refer only to the Eumycetes. 



The fungi may be unicellular or multicellular. In some, as the 

 true yeasts, the organism is ordinarily one-celled, though a few cells 

 may be temporarily attached in irregular clusters when actively 

 growing. Other fungi, however, may grow as one-celled organisms 

 for a time, or in a particular environment, and become multicellular 

 later or under changed conditions. Many of the fungi parasitic for 

 man and animals show this dimorphism, growing in one form in the 

 body, in another form on artificial culture media. 



Mycelium. The multicellular fungi are composed of cells arranged 

 end-to-end to form filaments or hyphae. These filaments branch 



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