CHAPTER X 



Soil Algae and Their Activities 



Introductory. The microscopic chlorophyll-containing forms of the 

 great plant division Thallophyta, the Algae, are represented in the soil 

 by three large groups: the Cyanophyceae, Chlorophyceae and Bacil- 

 lariaceae. The first contain, in addition to chlorophyll, also the pig- 

 ments phycocyanin and carotin and are, therefore, blue-green to violet 

 or brown in color; the second usually contain only chlorophyll, but some- 

 times also xanthophyll, and are, therefore, grass-green or yellow-green; 

 the third contain, in addition to chlorophyll, also carotin and xantho- 

 phyll, and are golden brown in color. The chlorophyll-bearing micro- 

 scopic forms of life are also represented in the soil by the Eugleneaceae 

 and the Cryptomonadaceae (or Flagellata and Dinoflagellata), com- 

 monly classified with the Protozoa (Flagellata), and by the filamentous 

 moss protonema, which belongs to the higher group of plants, the 

 Eryophyta. 



Algae and the autotrophic groups of bacteria are the only micro- 

 organisms in the soil that can synthesize organic matter from inorganic 

 materials, the fungi and the heterotrophic bacteria depend for their 

 energy upon organic matter synthesized by other forms of life. The 

 autotrophic bacteria obtain their energy chemosynthetically, using in- 

 organic substances as a source of energy; the algae obtain their energy 

 photosynthetically, using the energy of the rays of the sun. 



Algae are universally distributed on the surface of the soil, wherever 

 moisture and light are available. It is sufficient to moisten the soil 

 with water and expose it to the light to obtain in a short time an abund- 

 ant vegetation. However, algae may also be living below the surface 

 of the soil, not exposed to the direct rays of the sun and under more 

 uniform temperature and moisture conditions. The algae, as well as 

 the other groups of soil microorganisms grow in the soil in mixture and, 

 for purposes of identification and particularly for physiological investiga- 

 tions, they have to be isolated and cultivated upon artificially prepared 

 media. 



Some of the algae are isolated readily from the soil and others only 

 with difficulty. For morphological studies and classification, it is suffi- 



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