chap, hi The Absorption of Nitrogen 333 



becomes important. In the same year Molisch found that 

 nitrites are absorbed eagerly by the green plant when in 

 so dilute a solution as -05 per cent., but that they become 

 poisonous if present in too large amount. 



A long series of researches, extending from 1887 to 1896, 

 was carried out by Pitsch, who showed that as a nutritive 

 material ammonia comes second to nitric acid. In 1887 

 Baumann found that in uncultivated soil the greater part 

 of the combined nitrogen exists in the form of compounds 

 of ammonia, varying much in quantity according to the 

 nature of the soil ; nitrates are too small in amount to 

 estimate quantitatively. 



In 1890 Muntz published the results of a number of 

 experiments arranged to test the value of ammonium com- 

 pounds by cultivating plants in soil deprived of nitrates, 

 and under conditions which prevented the formation of 

 nitrites or nitrates ; he convinced himself that the only 

 source of combined nitrogen was the ammoniacal salts 

 which he supplied. Great care was taken to avoid all 

 possible contamination, and the experiments were rigorously 

 controlled. The plants used were maize, beans, hemp, and 

 barley. He found that they are all able to absorb the 

 nitrogen of ammonia through their roots and that such 

 combined nitrogen is sufficient for them. In 1900 Maze 

 also stated that in the case of maize and some other grasses, 

 Brassica and a species of Allium, ammonium compounds 

 are about equal in nutritive value to salts of nitric acid. 



There has been, however, since the time of Boussingault 

 an opinion which has been widespread and held tenaciously 

 that the normal green plant thrives best when its nitrogen 

 is supplied to it in the form of nitrates. This view has 

 replaced the older view of Liebig that this part is played 

 by ammonia and its compounds, an opinion based chiefly 

 upon the fact that in the decomposition of organic sub- 

 stances such as are presented by natural manures, the 



