THALLOPHYTA: FUXGI 103 



and other elements, particularly potassium, sodium, or calcium, and form 

 nitrates, which may later be utilized by green plants. The root of the 

 legume responds to the presence of these parasitic bacteria by forming 

 local enlargements called tubercles or nodules. 



Nitrifying bacteria also live in the soil but form nitrates in a different 

 way. The decomposition of organic matter by bacteria of decay yields 

 ammonia (NH^). This is oxidized, first to nitrites (NO2 compounds) 

 by Nitrosomonas, and then to nitrates (NO3 compounds) by Nitrohacter. 

 An interesting fact about these bacteria is that, although lacking chloro- 

 phyll, they are able to synthesize carbohydrate food from water and 

 carbon dioxide (or carbonates). They derive their energy, not from 

 sunlight, but from the oxidations that they carry on. With respect to 

 their nutrition, these bacteria, like green plants, are autotrophic, even 

 though they do not carry on photosynthesis. The process by which 

 they make their own food is sometimes called chemosynthesis. Such 

 autotrophic bacteria may have preceded all other forms of life on the 

 earth. In addition to the nitrifying bacteria there are other kinds that 

 are autotrophic. They oxidize sulphur, hydrogen sulphide, free hydro- 

 gen, methane, or iron compounds. Beggiatoa is a colorless filamentous 

 form that oxidizes hydrogen sulphide (H2S) to form water and sulphur, 

 storing the sulphur as yellow granules inside its cells. It is found in 

 sulphur springs. Certain iron bacteria oxidize ferrous iron compounds 

 to ferric hydroxide (FeOHs), which accumulates to form a kind of iron 

 ore. These bacteria are common in bogs. 



Denitrifying bacteria live in the soil, especially where poorly drained. 

 They convert nitrogen salts into gaseous nitrogen. This escapes into 

 the air and so causes a loss of soil fertility. 



Myxobacteria. The myxobacteria are a group of peculiar organisms 

 that live as saprophytes on animal refuse. Their cells resemble those of 

 true bacteria but form remarkable complex colonies held together by 

 mucilage. Some of the myxobacteria form stalked sporangia that are 

 often brightly colored. Some exhibit slow creeping movements. In 

 these respects the group resembles the myxomycetes. 



Summary. The Schizomycetes are the simplest of all plants. All of 

 them are unicellular, the cells being either solitary or in colonies. A defi- 

 nite cell wall is present, generally composed of chitin rather than of 

 cellulose, and usually breaks down to form mucilage. The protoplast 

 shows Httle organization, a nucleus being represented only by scattered 

 granules of chromatin. Reproduction occurs by fission. Some bacteria 

 move by means of cilia, while others are nonmotile. In some species a 

 resting cell (endospore) may form inside a vegetative cell, becoming 

 invested with a new cell wall. The Schizomycetes are closely related to 

 the Cyanophyceae, differing from them chiefly in the lack of chloro- 



