WATER RETAINED BY EQUAL WEIGHTS OF VARIOUS SOILS 



I = a coarse sand, 2 = peaty soil, 3 = alluvial loam, 4 = clay, 5 = clay after 

 puddling, in which case the bulk of the water has not percolated (/. 198). 



PHOTOGRAPHS OF CULTURES OF SOIL ORGANISMS 



1 = Moulds growing in medium containing ammonium salts but no cal- 



cium carbonate (p. 206). 



2 = Flask in which algae have appeared; notice the bubbles of oxygen. 



3 = Medium without nitrogen in which azolobacter has developed. 





EXPERIMENT TO 

 ILLUSTRATE 

 THE RISE OF 

 WATER IN SOILS 

 BY CAPILLAR- 

 ITY OR SUR- 

 FACE TENSION 



1 =clay, 



2 = loam, 



3 = fine sand, 



4 = coarse sand. 



Photograph taken twenty- 

 four hours after starting 

 the experiment (/. 199). 



