188 HOW CROPS GROW. 



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

 the common live-for-ever (Sedum telephium) no trace of 

 sodium detectable by ordinary means ; while in the ash 

 of the roots of the same plant there occurred 1.8 per 

 cent of its oxide ( Vs. St., IV, p. 190). 



It is possible then that, in the above instances, so- 

 dium really existed in the plants, though not in those 

 parts which were subjected to analysis. It should be 

 added that in ordinary analyses, where sodium is stated 

 to be absent, it is simply implied that it is present, if at 

 all, in too small a quantity to admit of determining by 

 the usual method, while in reality a minute amount may 

 be present in all such cases.* 



The final result of all the analytical investigations 

 hitherto made, with regard to cultivated agricultural 

 plants, then, is that sodium is an extremely variable in- 

 gredient of the ash of plants, and though generally pres- 

 ent 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 Xobbe & Sie- 

 gert have contributed experimental evidence bearing on 

 this question. 



The investigations of Salm-Horstmar were made with 

 great nicety, and especial attention was bestowed on the 

 influence of very minute quantities of the various sub- 

 stances employed. He gives as the result of numerous 

 experiments, that, for wheat, oats, and barley, in the 

 early vegetative stages of growth, Sodium, while advan- 

 tageous, is not essential, but that for the perfection of 

 fruit an appreciable though minute quantity of this ele- 

 ment is indispensable. ( Versuche und Resultate iiber 

 die Nalirung der Pflanzen, pp. 12, 27, 29, 36.) 



The methods of spectral analysis, by which ssnoj^nn of a pram of 

 sodium oxide may lie detected. < lemons) rate t his "element to lie so uni- 

 versally distributee" that it is next to impossible to find or to prepare 

 anything that is free from it. 



