INSUFFICIENT FOR PLANT-LIFE. 119 



36. per cent, until the blooming begins, 50. per cent, during 

 blooming, and 8.0 per cent, after that period, until the seeds 

 are ripe. 



The peculiar distribution of the available nitrogen com- 

 pounds of the air throughout the entire year apparently do not 

 comply, as to the time needed, with conditions as pre- 

 viously illustrated. 



As it is not prudent to trust to mere chance, when the 

 means which may secure success are Avithin oiir reach, we do 

 best to choose the safer course, and consider the atmospheric 

 supply of nitrogen insufficient for the purposes of intensive 

 farming. 



Having thus briefly pointed out what we assume about the 

 nature and the extent of the atmospheric supply of nitrogen 

 plant-food, it remains for me to treat of the relation in which 

 the soil stands to plant-life, as far as its function as a resource 

 of nitrogen is concerned. 



The soil contains nitrogen plant-food in three distinct forms ; 

 namely, as ammonia, as nitric acid, and as organic nitrogen- 

 ous compounds — resulting from decaying organic, vegetable 

 and animal matters. 



The ammonia of the soil is derived either from air or from 

 decaying organic substances. Its amount in Avell cultivated 

 land seems to be of constant quantity for every kind of soil, 

 and as a general rule much less than the earlier examinations 

 of Bustleiu, R. Hoffman, Wolft' and others represent. Ac- 

 cording to these authorities, there have been found from one- 

 half to two ten-thousandth parts of ammonia in various kinds 

 of soil. Progress in analytical modes of examination have 

 reduced those figures. 



W. Wolff and W. Knop, in their late valuable investiga- 

 tions, do not find it higher than from one hundred thousandth, 

 to one-millionth part of the soil. They found the ammonia 

 only in the surface layers. At six feet depth no trace could 

 be recognized. As neither rain-fall nor the presence of de- 

 ca3^ing organic matter seemed to affect this proportion for 

 any length of time, it is quite obvious that the soil ordinarily 

 must contain all the requirements to change the ammonia 

 continually into nitric acid. 



These facts regarding the behavior of the ammonia of the 



