14 BACTERIA AND SOIL FERTILITY 



Bryophytes, and thallus plants or Thallophytes. The thallus 

 plants have neither stems nor leaves, and comprise bacteria, algae, 

 and fungi. Fungi are simple plants devoid of chlorophyll. 

 Yeasts, molds, mildevi^s, smuts, and rusts also fall in this class. 



Nor is it an easy task to differentiate nicely between bacteria, 

 yeast, and molds. They may roughly be distinguished from each 

 other as follows: Bacteria are single-celled plants containing 

 nuclear material which is intimately diffused throughout the cell. 

 They multiply by transverse fission — a pinching in two at the cen- 

 ter of the organism. Sometimes they are united into long chains 

 which are easily separated into their separate links. Each link is 

 a complete organism. 



Yeasts are usually larger than bacteria. They are single-celled 

 organisms and have a definitely organized nucleus. This sets 

 them off from bacteria. They multiply by budding. Buds are 

 small protuberances which appear on the side of organisms which 

 enlarge forming two daughter cells. Molds consist of numerous 

 cells. These are a mass of interwoven threads, each thread being 

 composed of a number of cells which function as a unit. 



Where Do Bacteria Occur? — Bacteria are widely distributed, 

 occurring nearly everywhere. They are found in all soils, the 

 number varying with the kind of soil, quantity of plant and ani- 

 mal debris present, moisture, and treatment. They decrease in 

 number with depth, but many soils of Western America contain 

 numerous organisms even at a depth of ten feet. Although they 

 occur in air, it is not their normal home as under ordinary condi- 

 tions they cannot grow and multiply in it. The number and 

 variety found in air vary with a number of factors — location, 

 moisture, dust, movement of the atmosphere, and the presence 

 or absence of injurious gases. The atmosphere of some high 

 mountains is practically free from bacteria; city and country air 

 also differ from each other in the number and kind of bacteria 

 which they contain. There is a great variation in the air of build- 

 ings. They are especially numerous where dust is plentiful. 



Most natural waters contain great numbers of bacteria. In 

 sewage and polluted water they are especially numerous. They 



