GYPSUM INCREASING THE SUPPLY OP CARBON. 253 



Holstein, that if, on an extent of level ground sown with corn, 

 some fields be marled and others left uninarled, the corn on the latter 

 portions will grow less luxuriantly, and will yield a poorer crop 

 than if tlie whole had been unmarled. Hence, he adds, if the 

 occupier of the unmarled field would not have a succession of poor 

 crops, he must marl his land also. 



" Can it really be," continues Johnston, " that Nature thus re- 

 wards the diligent and the improver? Do the plants which grow 

 on a soil in higher condition take from the air more than their due 

 share of the carbonic acid or other vegetable food it may contain, 

 and leave to the tenants of the poorer soil a less proportion than 

 they might otherwise draw from it ?" (p. 101.) Like most other 

 readers, probably, I cannot venture to answer these questions 

 affirmatively. But if indeed calcareous earth in soil gives to plants 

 the power to seize upon and assimilate a much larger amount of 

 carbonic acid, it may well follow that other adjacent plants, not so 

 endowed, may in the contest fail to obtain their previously due 

 share of the always very small proportion of carbonic acid gas in 

 the atmosphere. 



In connexion with these interesting statements, I will add an- 

 other, which is fully believed by many persons, and which I have 

 also heard asserted by one of the best practical farmers of Virginia, 

 and who is also an intelligent and judicious observer. The opinion 

 referred to is, that if a narrow strip of a clover-field be omitted, for 

 experiment and observation, when all the adjoining ground is 

 dressed with gypsum (sulphate of lime), and the manure acts well, 

 that the omitted strip will produce worse clover than it would have 

 done if no gypsum was near. The farmers who maintain this pro- 

 position, do so simply upon having observed (as they conceive) 

 such facts. They had no theoretical views to support by such a fact, 

 and indeed they did not pretend to offer a supposed cause for such 

 an effect. For my own part, I have had no opportunity of observ- 

 ing any such facts, and will neither affirm nor deny such to have 

 been accurately observed by others. But such results seemed so 

 unsupported by reason, that at first I deemed the observations 

 mistaken, and the statements not worth any consideration. But by 

 applying the obvious deductions from Dr. Wight's experiments, 

 these before (supposed) irrational and incredible results may appear 

 well sustained, both in regard to their accuracy and their causation. 



2. Lime in soil increases the effect of azotized manures, and f 

 through leguminous plants, draws azote also from the atmo- 

 sphere. 



The quantity of carbon in plants, or in different products of 

 plants, amounts, in some subjects, to more than one-half of the 

 whole weight of the dry plant or product j and in all other cases it 



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