USEFUL ALGAE — CHASE 413 



Graebner listed the species of soil algae found in a plant com- 

 munity as a whole on the heaths of northern Germany and ascribes 

 to them great importance since they are the first immigrants on new 

 soil and cause the first formation of humus in poor soil. He enumer- 

 ated 31 species of Cyanophyceae, three species of Diatomaceae, and 

 18 species of Chlorophyceae found on these uncultivated heaths. 



Fritsch and Salisbury described the succession of cryptogams 

 (plants that do not bear true seeds) on burnt heath in England. 

 The first immigrants were the green algae Cystococcus hwmicola^ 

 Gloeocystis vesiculosa^ Trochiscia aspera^ and Dactylococcus infusi- 

 onuTTh. Various fungi grow in their mucilaginous envelopes, and by 

 degrees, lichens (a symbiosis of algae and fungi) appear. With 

 the formation of lichen thalli, filamentous algae, Mesotaenium vio- 

 lascens, Hormidium fjaccidwrri^ and Zygogonimn ericetonium appear. 



The investigation of a single locality in east Greenland has shown 

 that subterranean algae are present in the absolutely virgin soil 

 there. 



The soil in a rice field is inundated with water once or twice a 

 year for a period of 8 to 12 weeks. Holsinger found a quantity of 

 green and blue-green algae growing in this water. 



Harrison and Aiyer have shown, that a surface stratum composed 

 of algae and other organisms in the irrigation ditches of rice fields 

 plays an important part in the production of oxygen necessary for 

 the growth of rice roots. 



The cultivated paddy soils of the United Provinces (Benares, 

 Mirzapur, Gorakhpur, and Basti) consisting of large tracts covering 

 an area of at least 5,000 acres were investigated by Singh and found 

 to contain 43 species of green and blue-green algae that were at 

 a depth of 2 inches, 6 inches, and 12 inches. None were found in 

 the wet fields. When the soils dried up, the blue-green algae were 

 found to withstand desiccation longer than the green algae. 



Algae can withstand drought better than the higher plants. This 

 is illustrated during very dry periods in the summer when the grass 

 is killed by drought. Piercy has shown that the green alga Hor- 

 midium which lives through periods of dryness will then begin to 

 grow where the grass has been killed in the next succeeding damp 

 period, usually in the springtime, and will spread extensively. The 

 algae evidently help prepare the soil for the grass as numerous grass 

 seeds then germinate and form a dense carpet of grass which will 

 choke the algae and force them to disappear until the next summer 

 drought. 



Petersen and Puymaly have also described how the soil algae in 

 a garden walk are constantly competing with the grass weeds that 



