204 NATURE OF FUNGI 



and also by the fact that they bear tetraspores. The formation 

 of the tetraspores, however, is attended with a reduction of the 

 chromosomes by one-half, and these spores produce plants charac- 

 terized by the reduced number of chromosomes and also by the 

 fact that they bear the sexual organs. So in the Red Algae we 

 have very clearly brought before us the two generations in the 

 life of the plant, the sexual generation, characterized by the re- 

 duced number of chromosomes and the production of the sexual 

 organs, and the asexual generation, characterized by the double 

 number of chromosomes which appear in two spore-bearing 

 plants, i. e., the minute plant in the cystocarp and the tetraspore- 

 bearing plant. The distinction between the sexual and asexual 

 generation is emphasized at this point because we see in the algae 

 how it gradually became more and more conspicuous, and in the 

 mosses and succeeding groups it will be noticed that the relation 

 of these two generations is intimately associated with the evolu- 

 tion of the higher types of plant life. 



Subdivision 5. Eumycetes or True Fungi 



76. The Nature of Fungi. — The Fungi are the largest group 

 of the Thallophyta and include such familiar forms as moulds, 

 mildews, toadstools and mushrooms. The absence of chloro- 

 phyll is the most striking feature of these plants. They are 

 unable therefore to form sugar, starch and other foods from the 

 elements of the soil and air and must obtain them already manu- 

 factured. Consequently, they are either saprophytes living upon 

 decaying organic matter, or parasites preying upon living organ- 

 isms. The majority of fungi procure their food from decaying 

 plant and animal matter, and in this relation many of them are 

 of the same economic importance as the saprophytic bacteria. 

 Other forms exist as parasites upon living plants and animals. 

 In this relation fungi cause almost incalculable loss annually to 

 the country and frequently crops over large areas are ruined by 

 their depredations. The parasitic forms gain access to the host 

 through a wound, stoma or the delicate tissues of seedlings or 

 young parts of the plant, and in other cases the fungus forms a 



