84 MASSACHUSETTS HORTICULTURAL SOCIETY. 



roots in the soil? If they get nitrogen from the air, is it in the 

 form of combined nitrogen, ammonia, nitric acid, nitrous acid and 

 the like, of which the air contains only very minute quantities, or 

 are they able to make use of the free uncombined nitrogen which 

 makes up four-fifths of the whole weight of the atmosphere ? 



For fifty years these problems have been discussed, and during 

 that time chemists have been endeavoring to solve them by exper- 

 iment. For a long period a negative answer to both the questions 

 seemed probable. That is to sa}', the best experimental evidence 

 implied that the plants could not make use of the free nitrogen of 

 the air, and if they were able to avail themselves of the combined 

 nitrogen, the quantities they could get hold of would be too small 

 to be of much account. But of late the tendency of research has 

 been in the other direction. A number of experiments indicate 

 that plants do, somehow or other, get hold of a considei'able 

 quantity of atmospheric nitrogen, and within a short time, a 

 series of investigations seems to bring proofs, or at least, very 

 strong evidence, that certain plants are able to get and use, for 

 the building up of their tissues, the free nitrogen of the air. 



The doctrine that plants get nitrogen from the air has hereto- 

 fore been deemed very heterodox, yet people have wished it might 

 be true. The latest research teaches that nitrogen accumulated 

 in the soil is being removed by plants and also by leaching. 



Nitrogen is a valuable element, but hardest to hold. Given 

 plenty of the three elements phosphoric acid, potash, and nitro- 

 gen, and food is assured. It is a matter of common experience 

 in human history that when a great want arises, the means of 

 supply is found. Thus in regard to potash, when the soapboilers 

 outbid farmers in the purchase of ashes, the Stassfurth salts were 

 discovered, where the process of evaporation had been performed 

 by nature. These salts are now used all over our southern States 

 and in the coffee fields of Brazil and Ceylon. 



Fourth-fifths of the weight of the air around us is nitrogen, and 

 the question comes up, Can plants — can any plants — avail them- 

 selves of it? Boussingault and Lawes concluded that they could 

 not and that we are drawing for our nitrogen on the stores accum- 

 ulated in the ground in past ages. But there are facts which are 

 hard to explain on this hypothesis, and there is a feeling that, 

 after all, perhaps they do get it somehow. Microbes seem to be 

 working over the stores of inert nitrogen, and clover may favor 

 the action of microbes. 



