174 HOW CROPS GROW. 
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 
which 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 
guantity,* if at all, while in reality a minute amount may 
be present in all such cases.t 
The grand result of all the analytical investigations 
hitherto made, with regard to cultivated agricultural 
plants, then, is that seda is an extremely variable ingre- 
dient of the ash of plants, and though generally present 
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-Horstmar, Stohmann, Knop, and Nobbe & 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.” 
+ The newly discovered methods of spectral analysis, by which suand aaaT 
of a grain of soda may be detected, have demonstrated that this element 18 80 
universally distributed that it is next to impossible.to find or make anything that 
is free from it. 
