104 THE SOIL. 



84 OTammes : wliile he obtained from another Lidian corn 

 plant grown in the soil, at the same time and from the 

 same seed, a crop weighing 346 grammes. In Knop's 

 experiments, the dry weight of two Indian com plants, 

 the one grown in water, the other in the soil, was found 

 to be as 1 : 7. 



The water circulating in the soil contains chloride of 

 sodium, hme, and magnesia — the two latter in combina- 

 tion partly with carbonic acid, partly with mineral acids ; 

 and there can hardly be a doubt but that the plant 

 absorbs a portion of these substances from the solution. 

 The same must apply equally to potash, ammonia, and 

 the dissolved phosphates ; but the water circulating in the 

 soil, in a normal condition, either does not hold the three 

 last-named substances in solution, or not in sufficient 

 quantities to supply the demands of the plant. 



According to the ordinary rules of natiu-al science, 

 when Ave seek to explain a phenomenon, we leave out of 

 view" those cases in which the conditions superinducing 

 the phenomenon are clear and patent. For instance, if 

 we find in bog-water all the ash-constituents of duck- 

 weed, there can be no doubt about the form in which 

 they passed into the plant ; they were dissolved in water, 

 and they were absorbed in a soluble state. In such a 

 case, we have merely to explain the reason why the 

 several ash-constituents, being all present in one and the 

 same form, have yet passed mto the plant in unequal 

 proportions. 



If, in another case, we find that the rain-water which 

 falls on a given area of land, dissolves out of the soil many 

 times more potash than was contained in a crop of turnips 

 grown on that area, there is every reason to assume that the 

 turnip, hke the duckweed, has absorbed the needful potash 

 from a solution. But if in the entire quantity of water 



