NUTRIENT SALTS. 



69 



The other constituents of the ash of these plants, in particular iron oxide, mag- 

 nesia, and phosphoric and sulphuric acids, exhibited less marked differences; but 

 the inequality in the amounts of potash, soda, lime and silicic acid are so great, 

 as only to be explicable on the assumption of a power of selection on the part of 

 these plants. Various species of brown and red sea- weeds, which had been attached 

 to the same rock and developed in the same sea- water, showed similar variations 

 in the composition of their ash. 



On the mountains of serpentine rock near Gurhof, in Lower Austria, specimens 

 of Biscutella Icevigata and Doi^ycnium decumbens were collected from plants 

 growing together, and one above the other, upon a declivity which they clothed. 

 Their roots, interlaced here and there, were fixed in the same ground, and drew 

 nourishment from the same store. The following table gives the composition of 

 the ash in these two species: 



The differences here seem to be not so great as in the case of the water-plants 

 previously given, but they are sufficient to prevent our regarding them as merely 

 the result of chance. 



If, on the other hand, we compare the composition of the ash of different 

 specimens of the same species, which have been reared on similar soils, but at 

 great distances from one another, the discrepancies are comparatively slight. 

 Foliage from beech-trees growing on the limestone mountains near Regensburg 

 yielded an ash practically identical with that obtained from leaves of beeches on 

 the Bakonyer-Wald hills in Hungary. The ash of different individuals of a single 

 species even exhibits the same constitution, in the main, when those individual 

 plants have obtained their nutriment from soils differing greatly in chemical 

 composition. Only in cases where the quantity of a substance in one soil is 

 more abundant than in the other there is generally a greater or less amount of it 

 to be found in the ash. 



That under these circumstances certain substances may replace one another is not 

 improbable. But such substitution must be confined to those nearly allied com- 

 pounds whose molecules are capable of being used indifferently by the formative 



