CHAPTER IV 

 THALLOPHYTA: FUNGI 



Fungi are dependent (heterotrophic) thallophytes. Lacking chloro- 

 phyll, they are unable to carry on photosynthesis and hence must obtain 

 their food from an external source. Many are saprophytes, living on 

 dead organic matter; others are parasites, obtaining nourishment from 

 the bodies of living plants or animals, the organism attacked being the 

 host. At least some of the fungi may have evolved directly from the 

 algae through loss of power to carry on photosynthesis. Because of 

 their relation to the decomposition of organic matter and to disease, 

 fungi are of tremendous economic importance. The fungi comprise the 

 five classes Schizomycetes, Myxomycetes, Phycomycetes, Ascomycetes, 

 and Basidiomycetes. To these might be added the class Lichenes. 



1. SCHIZOMYCETES 



The Schizomycetes, or bacteria, are similar in many respects to the 

 Cyanophyceae, differing from them chiefly in their smaller size and lack 

 of chlorophyll. In fact the two groups are often combined into a single 

 group, the Schizophyta. The bacteria are at once the smallest and 

 simplest of all known organisms, unless the viruses are to be considered 

 as living. They are also the most widely distributed, occurring under 

 all conditions where life may exist — in fresh and salt water, in soil, in 

 the air, and in the living and dead bodies of other organisms. Like the 

 Cyanophyceae, they are a very ancient group and must have been among 

 the first forms of life to have existed on the earth. The bacteria com- 

 prise about 1,500 species. Some common genera are Streptococcus, 

 Micrococcus, Sarcina, Bacterium, Bacillus, Pseudomonas, Microspira, 

 Spirilhim, Cladothrix, and Beggiatoa. 



Structure and Reproduction. Like the blue-green algae, bacteria are 

 unicellular plants that reproduce by fission. Their cells are of three 

 general types: spherical (coccus) forms, rod-shaped {bacillus) forms, and 

 curved or spiral (spirillum) forms (Fig. 80). Some are nonmotile, while 

 others bear cilia, by means of which they move rapidly. The cilia 

 may cover the entire cell or may be restricted to one or both ends, where 

 they occur either singly or in tufts. The rod-shaped types average about 

 2.5ii in length,! while many of the spherical forms are only about 0.5^ 

 in diameter. 



' The unit of microscopic measurement is the viicron, abbreviated ju- It is one- 

 thousandth of a millimeter (0.001 mm.), approximately equivalent to 1/25,000 inch. 



100 



