Ill 



cereals for instance, it would be of no advantage 

 whatever to supply any additional potash, lime, 

 or phosphoric acid ; they would not tend to in- 

 crease the yield ; for, in the absence of silica, the 

 plant cannot make use of the large store of the 

 other inorganic food constituents, so that any 

 additional supply of these substances would be 

 simply throwing away money and labour ; but 

 were a proportionate quantity of available silica, 

 the defective element, supplied, we would then 

 be giving the only substance necessary to make 

 the soil yield most abundant harvests. 



The particular manure, then, required for a 

 certain crop, can only be determined by the most 

 intimate knowledge of the natural condition and 

 requirements of the soil on which it is to be grown. 



Most soils contain one or another of the inor- 

 ganic substances required by plants in minutest 

 quantity, out of proportion to the others ; and 

 it has been mentioned that the experiments made by 

 Prince Salm Horstmar showed that, in the absence 

 of any single mineral in the soil, plants, after 

 having exhausted the small quantity contained in 

 the seed, will either perish after making a feeble 

 attempt to grow, or, as in the absence of phosphoric 

 and sulphuric acid, will not bear any seed ; so that 

 we can conclude from these experiments that an 

 insufficiency of any of these inorganic plant 

 constituents in the soil will most seriously inter- 



