SOIL ALGAE 225 



and algae was present in cultivated soils. In these soils, 64 species 

 and varieties of algae consisting of 24 species of Cyanophyceae, 20 

 Chlorophyceae and 20 Bacillarieae (diatoms) were found. The most 

 important species in the plant-formation are Hantzschia amphioxys, 

 Trochiscia aspera, Chlorococcum humicola, Bumilleria exilis and, to a 

 less degree, Ulothrix subtilis var. variabilis; moss protonema was 

 universally present. 



There seemed to be an association between three blue-greens; namely, 

 Phormidium tenue, Ph. autumn ale and Plectonema battersii, two of which 

 were found together in 16 of the samples and all three in 7 samples. 

 Soils rich in blue-greens contained only a few species of diatoms, and 

 vice versa; the first occurred more frequently in arable soils and the 

 second in old garden soils. The resting forms could survive desiccation 

 for a long period of time; 35 9 species of blue-green algae, 4 grass-greens 

 and 1 diatom were isolated from soils stored for about 40 years; the 

 Nostoc muscorum and Nodularia harveyana retained vitality for the 

 longest period of time. 



Most of the algae, except a few diatoms, are severely affected by frost, 

 so that their numbers and activities usually reach a minimum in Febru- 

 ary. As soon as the snow melts a rapid development takes place, 

 followed again by a minimum growth in the late summer. 36 With an 

 increase in moisture, there is an increase in the numbers and activities. 

 However, this phenomenon is not absolute. Observations by West 

 and others indicate that different species of fresh water algae attain their 

 maximal growth at different periods in the year. Soil algae show a 

 similar variability. 



The determination of numbers of algae in the soil is even less accurate 

 than in the case of bacteria, fungi and protozoa, largely because of the 

 layer of mucilage with which the cells of various species are surrounded. 

 The dilution method may be used, in a manner similar to the determina- 

 tion of numbers of protozoa; 37 a nutrient solution (p. 221) is used for the 

 preparation of the different dilutions, and 5-cc. portions of the final 

 dilutions are added to test-tubes containing 15-gram portions of 



35 Bristol, B. M. On the retention of vitality of algae from old stored soils. 

 New Phyt. 18, 1919, Nos. 3 and 4; 1920 (p. 92-107). 



36 France, 1921 (p. 642). Magedeburg, P. Vergleichende Untersuchung der 

 Hochmoor-Algenflora zweier deutscher Mittelgebirge. Hedwigia. 66: 1-26. 

 1926. 



37 Bristol Roach, B. M. Methods for studying soil algae. Abderhald. Handb. 

 Biochem. Arb. Meth. Abt. XI, T. 3. 1926. 



