INTERDEPENDENCE OF HIGHER PLANTS AND MICROBES 183 



Providing that the nitrogen content of the material under consid- 

 eration is sufficiently great, there may be a rapid transformation 

 of the nitrogen to forms available for plant growth. 



Non-symbiotic nitrogen fixation may, under certain conditions, 

 be sufficient to produce appreciable effects upon plant development. 

 Microbial disintegration of plant residues and organic fertilizers 



Interchange with the Free Atmosphere 



Movements of Carbon Dioxide about Growing Plants 



Soil Surface 



Soil Surface 



Carbon Dioxide of the Soil of Microbial Origin 



Fig. 70. — Diagrammatic representation of the movements of carbon dioxide 

 between soil and atmosphere about plants (after Lundegardh). 



may exert beneficial effects on the development of higher plants, 

 not only through the roots but also through the aerial parts of the 

 plant; this effect is associated with the increase in the concentra- 

 tion of carbon dioxide in the zone of leaf absorption. During the 

 warm seasons and in periods of bright sunlight the absorption of 

 carbon dioxide appears to be more rapid than its supply from 

 the soil. This is clearly apparent from Fig. 69. Where fight 



