APPENDIX A 603 



roles in discussing the colorless plants in Chap. XIII, the geological history of 

 plants in Chap. XXVI, and the biotic environment in Chap. XXXIII. We need 

 no more than briefly recall some of the points there discussed. 



The decay-causing, saprophytic bacteria destroy the dead bodies of animals 

 and plants and thus make the compounds locked up in them available for reuti- 

 lization by living things. The nitrifying and nitrogen-fixing bacteria add nitrates 

 to the soil and make possible the synthesis of proteins by plants. Symbiotic 

 bacteria in the intestines of herbivorous vertebrates and insects break down the 

 otherwise indigestible cellulose of plants and make it available to the animals 

 as a source of carbohydrate food. Man makes use of many kinds of bacteria in 

 the preparation of food, in industrial processes, in sewage disposal, and in other 

 ways. 



The Slime Molds (Myxomycetes) are among the most primitive of the thallo- 

 phytes, and, although we have included them among the fungi, they are so unlike 

 other plants that they are sometimes given rank as a distinct phylum. In their 

 vegetative state they consist of a mass of protoplasm, slimelike, usually dirty 

 white or yellowish in color, containing many nuclei but not divided into cells. This 

 multinucleate, noncellular mass of protoplasm — often as much as a cupful in a 

 single slime mold — shows active creeping movements. It can spread out in a thin 

 network and, amoebalike, move about over the surface of the material on which 

 it grows. It avoids light and seeks moisture; rotting heaps of leaves and decaying 

 logs are favorite habitats. A slime mold reproduces by transforming most of its 

 mass into spores, borne on stalks; the spore masses and stalks are of various colors 

 — brown, black, red, orange, etc. When the spores fall into water or upon moist 

 surfaces, they germinate into small ameboid or flagellated single cells. These move 

 about, feed, and grow; if they touch others of their kind, they fuse with them, and 

 by such growth and amalgamation a new multinucleate slime mold is in time 

 produced. 



The True Fungi (Eumycetes) include a host of species showing the utmost 

 diversity in form and mode of life. Among them are the yeasts, responsible for 

 various types of fermentation, and used by man for raising bread, making beer, 

 and for other purposes. The majority of the fungi are saprophytes, but many are 

 parasites of animals (Fig. 33.1) or of plants (Fig. 33.2), and these are the cause 

 of serious diseases and great economic loss. 



About the same range in structural pattern occurs in the fungi as in the algae — 

 from unicellular types, through loose cell aggregations, to types with a multi- 

 cellular thallus in which the beginnings of cell differentiation and division of 

 labor are shown. Many of the higher fungi have holdfasts and stalks comparable 

 to those of the brown and red algae, but no fungus possesses anything that corre- 

 sponds with the blades of these algae or with the leaves of higher plants. Fre- 

 quently the thallus of the higher fungi forms a mass of fine, threadlike strands 

 called mycelia (ml sel' i a) ; mushrooms, which we commonly think of when fungi 

 are mentioned, are, in fact, only the fruiting bodies of a mycelial thallus, which 

 ramifies through a mass of decaying leaves or other food source from which the 

 mushroom appears to sprout. Peculiar modifications of the thallus occur in many 

 parasitic fungi, related to special requirements of parasitic existence; thus in 

 certain groups, some of the mycelial filaments form specialized organs called 



