174 HOW CROPS GEOW. 



Although, as just indicated, soda has been found want- 

 ing in the wheat kernel and in potato tubers, in some in- 

 stances, it is not certain that it was absent from other 

 parts of the same plants, nor has it been proved, so far as 

 we know, that soda is wanting in any entire plant which 

 has grown on a natural soil. 



Weinhold found in the ash of the stem and leaves of the 

 common live-for-ever, {Sedum, telephium^ no trace of soda 

 detectable by ordinary means ; while in the ash of the 

 roots of the same plant, there occurred 1.8 per cent of this 

 substance. ( Vs. St., IV, p. 190.) 



It is possible, then, that, in the above instances, soda 

 really existed in the plants, though not in those parts 

 wliich were subjected to analysis. It should be added 

 that in ordinary analyses, where soda is stated to be ab- 

 sent, it is simply implied that it is present in unweighable 

 quantity* if at all, while in reality a minute amount may 

 be present in all such cases.f 



The grand result of all the analytical investigations 

 hitherto made, with regard to cultivated agricultural 

 plants, then, is that soda is an extremely variable ingre- 

 dient of the ash of plants, and though generally pyresent 

 in some proportion, and often in large proportion, has 

 been observed to be absent in weighable quantity in the 

 seeds of grains and in the tubers of potatoes. 



Salm-Ho.rstmar, Stohmann, KnojD, and Ifobbe & Sie- 

 gert, have contributed certain synthetical data that bear 

 on the question before us. 



The investigations of Salm-Horstmar were made with 

 the greatest nicety, and especial attention was bestowed 

 on the influence of very minute quantities of the various 



* Unweighable quantities are designated as " trace " or " traces." 



t The newly discovered methods of spectral analysis, by which ~__.j^|^_^^^ 

 of a grain of soda may be detected, have demonstrated that this element is so 

 universally distributed that it is next to impossible to fUid or make anything that 

 is free from it. 



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