2o6 F. E. Fritsch 



where photosynthesis is possible, and therefore an intensive study 

 of surface-growing Algae and of their conditions of existence is 

 in the future likely to produce results more valuable to science 

 than a study of their occurrence in the subterranean habitat. Soil 

 Algae have also been credited with fulfilling another function, 

 namely, in respect to nitrogen fixation. A direct fixation of nitro- 

 gen by Algae, and particularly by Green Algae, is certainly 

 highly unlikely, and no data brought forward in this connection 

 have stood the test of a critical examination.''*' It is a demonstrated 

 fact, however, that nitrogen-fixing Bacteria in cultures bind an 

 increased amount of nitrogen in the presence of Algae. It is sug- 

 gested that a possible reason for the beneficial effect of the Algae 

 is that they remove the nitrogenous products of the activity of 

 the Bacteria or provide in their mucilage envelopes a carbo- 

 hydrate supply for the Bacteria. Clearly, however, the value of 

 Algae in relation to nitrogen fixation beneath the illuminated 

 zone of the soil must depend, in large measure, on their being 

 in a condition of active growth and multiplication, and of that 

 I believe no adequate proof has so far been presented. At pres- 

 ent, therefore, I am inclined to doubt that soil Algae are funda- 

 mentally important to the nitrogen-fixing Bacteria except in 

 those layers of the soil which are accessible to light and where 

 rapid growth and multiplication of the Algae can take place. 



I am fully cognizant that the suggestions presented here con- 

 cerning the source and nature of the subterranean algal com- 

 munity, although supported by a certain amount of fact, require 

 to be proved by diverse direct investigations. I feel, however, that 

 there is so much that is debatable in existing views concerning 

 the subterranean algal flora that a critical consideration of the 

 available facts was desirable. I hope that an experimental testing 

 of the accuracy of my suggestions will not be long delayed. 



