230 PRINCIPLES OF SOIL MICROBIOLOGY 



cleaned, sterilized sand. The inoculated tubes are placed in closed glass 

 vessels and exposed to sunlight. The presence and type of growth are 

 determined at the end of a month by microscopic examination. 



Occurrence of algae in the soil. Several heterogeneous groups of 

 Thallophytes are commonly included among the algae; they all contain 

 chlorophyll, which is often accompanied by other pigments. Phylo- 

 genetically, the algae belong to different groups of organisms: the 

 Cyanophyceae (Myxophyceae) or blue-green algae are related to the 

 bacteria or Schizomycetes. F. Cohn united both of these groups into 

 the Schizophyta, characterized by lack of a nucleus. The Flagellata 

 and Dinoflagellata (forming thick-walled resting cysts) are related to 

 the protozoa and are often included with these organisms. The Bacil- 

 lariales, characterized by their shells and auxospore formation, stand 

 apart also. It is also difficult to establish the relationship of the Charo- 

 phyta, Phaeophyceae, and Rhodophyceae. 



Without going into a detailed discussion of the classification of algae, 

 it is sufficient to indicate that comparatively little work — a few isolated 

 investigations — has been done on their occurrence in the soil. To 

 indicate the very incomplete nature of the records, it is sufficient to call 

 attention merely to the representatives of each group which have been 

 demonstrated to be present in the soil (Table 15). 



Biochemical activities of algae. 42 Algae are able, in the light, to 



38 For a classification of the blue-green algae, see Tilden, J. E. Minnesota 

 algae. I. Myxophyceae. Minn. Bot. Survey. 1910; Tilden, J. E. Synopsis 

 of the blue-green algae -Myxophyceae. Trans. Amer. Microscop. Soc. 36, 1917, 

 179-266; Forti-Sylloge Myxophycearum. See also the general texts of de Toni, 

 Engler and Prantl, and West; Collins, F. S. A working key to the genera of 

 North American Algae. Tufts College Studies, 4: No. 8. 1918. 



39 For a classification of diatoms see vol. x by Schonfeldt of Pascher's series, 

 and van Heurck, Traite des Diatom<5es. 



40 For a classification of the grass-green algae see West, Pascher, De Toni and 

 Collins. 



41 Moore, G. T., and Carter, N. Further studies on the subterranean algal 

 flora of the Missouri Botanical Garden. Ann. Mo. Bot. Gard. 13: 101-140. 1926. 



42 The following contributions should also be consulted on the carbon utiliza- 

 tion of algae: Artari, A. Zur Ernahrungsphysiologie der griinen Algen. Ber. 

 deut. bot. Gesell. 19: 7. 1901; Jahrb. wiss. Bot. 52: 410-466. 1913; 53: 527-535. 

 1914; Chodat, 1913 (p. 220) ; Bokorny, Th. Zur Kenntnis der physiologischen Fa- 

 higkeiten der Algengattung Spriogyra und einiger anderen Algen. Vergleich mit 

 Pilzen. Hedwigia, 59: 340-393. 1918; Dangeard, P. A. Observation sur une 

 algue cultivee a l'obscurite depuis huit ans. Compt. Rend. Acad. Sci. 172: 254- 

 260. 1921; Grintzesco, J. Contribution a l'etude des Protococcoidees: Chlorella 

 vulgaris Beijerinck, Rev. Gen. Bot. 15: 5-19, 67-82. 1903; Ternetz, C. Beitrage 



