1 64 



SOIL CONDITIONS AND PLANT GRO WTH 



TABLE XLIV. ANALYSES SHOWING CONCENTRATION OF IRON, ALUMINA, 

 AND ORGANIC MATTER IN THE PAN. 



Mayer (194), extending the earlier work of Emeis, 1 sup- 

 posed that anaerobic conditions arose during part of the year 

 when the land was waterlogged, and humic acid was then 

 formed and the iron reduced to the ferrous state. Ferrous 

 humate is soluble in water and therefore washes downwards : 

 even aluminium silicate becomes partly soluble. At a certain 

 depth this ceases ; various causes may come into play : the 

 water table may be reached, or there may be an accumulation 

 of washed-down clay on which the humates are precipitated. 

 Then in the dry part of the year oxygen can gain access to 

 this depth, converting the ferrous humate to ferric humate, 

 which being insoluble is protected against further washing. 



Ramann modified this somewhat by assuming that pre- 

 cipitation occurred when the solution of iron humate reached 

 the zone, intermediate between the surface soil and the sub- 

 soil, where he supposes weathering to be still proceeding and 

 where, therefore, there is a larger proportion than usual of 

 soluble reactive mineral salts. 



As an alternative Hall suggested that the solvent is CO 2 : 

 the iron is reduced to the ferrous state by the organic matter 



C. Emeis, Waldbaulkhe Forschungen und Beirachtungen, Berlin, 1875. 



