GROUPS OF PLANTS. 17 



or vegetable matter, when they are known as saprophytes. The 

 living plant or animal attacked by a fungus is known as the host. 



Fungi are especially characterized by the habit of arising 

 from spores and of producing thread-like cells the growing point 

 of which is at the apex. These threads are known as hyph^ 

 (singular hypha). They branch and become interwoven, forming 

 a mass or mat known as the mycelium (Fig. 13). The myce- 

 lium constitutes the plant body proper, and absorbs the food 

 material from the substratum, which it ramifies, often causing 

 decay. The mycelium is frequently not visible, and the presence 

 of the fungus is not recognized until the so-called fruit bodies are 

 developed, as sometimes seen in the case of mold}- oranges, 

 mildewed linen, and as illustrated by the common mushroom. 

 The mycelium has a cellulose wall which in some cases is modi- 

 fied to chitin, a nitrogenous substance related to animal cellulose 

 and found in crabs and other lower animals. The protoplasm 

 either occurs in a more or less delicate form lining the hyphse and 

 enclosing large vacuoles, or is comparatively dense enclosing 

 numerous small vacuoles. Many fungi contain color substances 

 which are dissolved in the cell-sap and are of a quite brilliant hue. 

 One of the most interesting classes of substances produced by 

 fungi is that of the ferments, including the oxidizing ferment 

 allied to laccase. They contain also amido-substances related to 

 lecithin ; fats ; carbohydrates, as trehalose and mannitol ; organic 

 acids, as oxalic, tartaric, malic, etc. ; and calcium oxalate may 

 be present in some cases. 



Reproduction in the Fungi is chiefly by means of asexual 

 spores, which arise in two ways. In the one case they are devel- 

 oped in a special cell or sporangium at the end of a mycelial thread 

 and are known as endospores. In the other case they arise ofi 

 special hyphse, or directly from the mycelium and are known as 

 EXOSPORES or conidia. There are also several modifications of 

 these two types of spores, which may be referred to later. 



Groups of Fungi. — There are two principal groups of Fungi, 

 namely, (i) the Phycomycetes, or Alga-fungi, so called because 

 they show a resemblance to certain of the Algae, and (2) the 

 Eumycetes, or true Fungi. The Eumycetes have two sub- 

 divisions, namely, (i) Ascomycetes and (2) Basidiomycetes. 



