SOURCES OF NITROGEN OF PLANTS. 95 



of the heaviest crops ever raised. "What is the office of this combined nitrogen, 

 Tvhat relation does it bear to plant nutrition? To summarily dismiss this large 

 amount of combined material by calling it inert "of no more use than the free 

 nitrogen of air" is to make a hasty generalization. Is it incapable of assimi- 

 lation by all kinds of plants and agriculturally to be considered " light as a 

 puff of empty air?" 



Has not the epithet "inert" been applied -without due consideration? 



Four years ago I began a series of experiments on the relations of this 

 organic nitrogen of the soil to plant growth, and three years ago I read an. 

 article on this subject at the Farmers' Institute, at Armada. The quantitative 

 estimation of the nitrogen in these experiments had not then been made. The 

 experiments have been continued year by year, and the results of these trials 

 and the estimation of the nitrogen are now given. 



CONDITIONS OF THE EXPERIMENT. 



In order to determine whether any material is essential to the growth of a 

 plant we endeavor to raise a plant in the entire exclusion of this one material,, 

 every other substance found in plants being furnished in sufficient amount. 

 If the plant makes complete growth, growing "from seed to ripen perfect 

 seed," and makes a healthy growth in complete absence of any given substance, 

 then we say that substance is not necessary to the growth of that plant. But 

 if the want of any given element is uniformly attended by unhealthy growth 

 and incomplete development, then such substance is said to be essential tO' 

 plant growth. Nitrogen is one of these essential elements, and no plant can 

 make perfect growth without it. 



If now a plant is supplied with every chemical element of growth in available 

 form except nitrogen, and this only in some particular form of combination,, 

 the question is settled that the plant can obtain its supply of nitrogen from 

 this particular combination if it makes perfect growth under these conditions.. 

 So also if one class of plants will make complete growth under these conditions, 

 while other classes fail to make such perfect growth, the question is settled 

 about the relative power of these two classes of plants to supply themselves 

 from this source of nitrogen. 



For this purpose an artificial soil must be used from which all other forms of 

 combined nitrogen are excluded, and no form of combined nitrogen obtain 

 access to it in the form of rain or dew, which usually contain ammonia and 

 nitrates in small amovint. 



The body of such artificial soil was made of silicious sand which had been, 

 heated red hot to expel any ammonia and nitrates; the vessels used to hold the 

 soil were new flower pots which had been heated red-hot for some time ; the 

 mineral matter was supplied by wood ashes, and a little pure soluble phosphate 

 of lime ; the water was distilled and made as free as possible from ammonia ; 

 the plants grown in a glazed room, freely exposed to light, but shut off from 

 rain and dew, and finally 13 per cent of swamp muck was added to the soil as 

 the source of combined nitrogen, this muck being a fair representative of the 

 average humus of the soil. 



A part of the nitrogen of humus is called active because it is readily con- 

 verted into ammonia by boiling with caustic lime, but a part is incapable of 

 readily forming ammonia, and hence is called inert. In order to discriminate 

 between the active and inert forms of the nitrogen of humus, two parallel series 

 of experiujents were carried on, one with humus in the natural state, and one 



