(39 



From the data presented above it is evident that in the decay of 

 wood or leaves or, in general, of plant tissues, alkaline carbonates 

 are f nrnished to the soil. It may be that the processes of decay will 

 furnish at the same time organic acids stronger than carbonic acid 

 and in sufficient qtiantity to combine with all the bases and prevent 

 an alkaline reaction. As has been shown in this laboratory carbonic 

 acid itself may be formed in stifficient amounts to convert all the 

 carbonates to the form of bicarbonates and thus prevent an alkaline 

 reaction. There is not sufficient evidence to justify a positive state- 

 ment, but it would seem probable that this can not be always the case 

 and that in fact there is alkali formed by the decay of plant tissues. 

 In humid regions the alkali thus formed is removed by leaching or 

 similar processes and by chemical reactions with the other soil com- 

 ponents, for which reactions water is necessary. 



In the arid regions, such as are found in the western part of the 

 United States, peculiar j)henomena, due to the special conditions 

 there existing, have been observed. The indigenous plants which are 

 found on the alkali lands are comparatively few in number, both as 

 to species and as to individuals: others have been artificially intro- 

 duced. They all have the property of absorbing more or less large 

 amounts of water-soluble mineral salts and on analysis all show 

 characteristically large percentages of bases. When the leaves or 

 debris from these x^lants have decomj^osed there is often found greater 

 or less accumulation of carbonates, although before the plant was cul- 

 tivated that i)articular region may have been qtiite free from soluble 

 carbonates. The decay of any organic matter with the accoDipany- 

 ing formation of carbonic acid in a soil containing soluble salts of the 

 alkali metals must be expected to result in the formation of soluble 

 carbonates, partly by dissolving lime or magnesitim compounds, fol- 

 lowed by stibsequent metathetical reactions or double decompositions 

 with the alkali salts; more slowly and in lesser degree, i^erhaps, but 

 nevertheless stirely, if the formation of carbon dioxide is continued, 

 by a distribution of the base between the two acids. This last i)roc- 

 ess, however, is probably of decidedly minor importance in the phe- 

 nomena under consideration. 



Owing to the conditions of climate and drainage existing in the 

 arid regions these carbonates when formed are not leached away, as 

 in the humid regions, and gradually accumulate to the more serious 

 detriment of the soil. 



COMPARISOX OF ANALYSES. 



For the purpose of comparison, two analyses of greasewood (Sarcoha' 

 tits vermiculotus) ash are here quoted, the first published by llilgard,^ 

 and the other by Goss and Griffin.^ 



- University of California, Report of Agr. Exp. Sta., p. 142 (1890). 



-Xew Mexico College of Agr. and Mech. Arts. Agr. Exp. Sta., Bu. •2-^. p. 41 



(1H9T,. 



