ON THE CHEMICAL CONSTITUENTS OF SOILS. 247 



exert an injurious or poisonous action. The analy- 

 ses are those of Dr. Sprengel, — a chemist who has 

 unceasingly occupied himself for the last twenty 

 years in endeavoring to point out the importance 

 of the inorganic ingredients of a soil for the develop- 

 ment of plants cultivated upon it. He considers as 

 essential all the inorganic bodies found in the ashes 

 of plants. Now, although we cannot coincide with 

 him in the opinion, that iron and manganese are in- 

 dispensable for vegetable life, (for these bodies are 

 found as excrementitious matter only in the bark, 

 and never form a constituent of an organ,) yet we 

 gratefully acknowledge the valuable services which 

 he has rendered to agriculture, by furnishing a natu- 

 ral explanation of the action of ashes, marl, &c., in 

 the improvement of a soil. Sprengel has shown, 

 that these mineral manures afford to a soil alka- 

 lies, phosphates, and sulphates; and further, that 

 they can exert a notable influence only on those 

 soils in which they are absent or deficient. In a 

 former chapter of this book I have endeavored to 

 point out the importance of considering these con- 

 stituents as intimately connected with the vital pro- 

 cesses of the vegetable organism, and have shown 

 that the different families of plants contain unequal 

 quantities of inorganic ingredients. This subject 

 has been left unexamined by Sprengel, yet it is one 

 of much importance ; for the application of manures 

 must be regulated by the composition of the plants 

 which are cultivated on any particular soil. Still, 

 the composition of the soil must always be kept in 

 view. Thus it would be perfect extravagance to 

 manure certain soils with marl, ashes, or gypsum; 

 whilst, on the contrary, these compounds would pro- 

 duce the most beneficial results on other lands. 



In a former part of the work, the principal action 

 of gypsum upon vegetation was ascribed to the de- 

 composition and fixation of the carbonate of ammonia 

 contained in rain-water ; but gypsum exerts a two- 

 fold action. The power of decomposing carbonate 



