. SECOND REPLY. 165 



are often covered with a thick crust of salt, showing them- 

 selves to be the ancient bottom of some dried-up sea, and 

 here these plants are found growing in the same abundance 

 and luxuriance as in the west of France. On the northern 

 coast of Germany, the little pale- red Maiden-pink grows 

 upon the arid sand-dunes, and is universally distributed 

 over the sandy plains of northern Germany ; but these are 

 succeeded by the granite, clay-slate, and gypsum of the 

 Hartz, the porphyry and Muschelkalk of Thuringia, and 

 our little pink is not met with again till we arrive at the 

 Keuper-sand plains, on the further side of the Maine, 

 surrounding the venerable city of Nuremberg. It extends 

 further south, through the Palatinate, till the Muschelkalk 

 of the Swabian Alps again sets a limit to it ; but it leaps 

 over these and the whole Alpine region, and at last appears 

 again on the sandy soils of northern Italy. How is it that 

 these plants everywhere disdain the richest soils in their 

 range of geographical distribution, and are confined to 

 perfectly determinate geognostic formations? Must not 

 the lime, the salt, the sand, or rather the silex, have a most 

 distinct influence in the matter? 



And it may further be asked : How does it happen that 

 one and the same soil can bring the one plant to the 

 highest state of development, while another soil is not able 

 to sustain its life ? Wherefore is it, lastly, that we see 

 the life and healthy condition of most of our cultivated 

 plants so distinctly connected with the manuring of the 

 soil with organic substances ? This question has been first 

 answered in a profound and truly scientific manner by 

 Liebig. How is it, he asks on the other side, that wheat 

 does not flourish in soils rich in humus, in pure vegetable 

 mould ? Because wheat contains a substance, silex, with- 

 out which it cannot exist, and which it does not find in 



