SECOND REPLY. 161 



by rivers to the sea. The much more accurate estimates 

 of Dausse for the Seine, and Dalton for the Thames, show 

 that we may at least assume one-third. Still more exact 

 are the statements of Berghaus with regard to the lower 

 part of the Rhine's course, and Studer's for the Upper 

 Rhine ; according to which, in the former case three-fourths 

 and in the latter four- fifths of all rain, snow and dew, runs 

 away through the Rhine. Lastly, the facts respecting the 

 Weser, published by Berghaus, and going very much into 

 detail, are such, that it becomes almost probable that this 

 river carries away even more water than atmospheric pre- 

 cipitation can furnish ; therefore, that some other natural 

 process must supply it with water. However, if we assume 

 that altogether only half the rain-water flows away, we yet 

 see how improbable it is that the remaining 1,162,500 Ibs. 

 of water, putting evaporation out of the question, can cover 

 the necessities of the plants, which amount to from three to 

 six millions. The watery vapour of the atmosphere must, 

 therefore, be brought to the plant in some other way, and 

 this happens through the property of absorbing the mois- 

 ture of the atmosphere, which is possessed by most of the 

 constituents of the soil. No substance possesses this 

 property in so high a degree as the humus, originating 

 out of the gradual decomposition of organic matters. The 

 humus is also remarkably distinguished for its special power 

 of extracting and, as it were, collecting the carbonic acid 

 and ammoniacal gas of /the air ; no solid substance of the 

 soil equals it in this particular, and water itself only ranks 

 second after it. Humus consequently contains, under all 

 circumstances, water impregnated with carbonic acid and 

 ammonia, and in proportion as this is withdrawn from it 

 by the roots of the plants, the loss is replaced out of the 

 atmosphere. This is certainly the principal road by which 



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