THE PROTEINS 39 



take place when nitrogen is being taken up by the 

 organism. The mystery of their formation is by 

 no means elucidated yet, although many workers 

 are endeavouring to throw light on the subject by 

 organic analysis and synthesis. In plants, nitrogen 

 is taken up as nitrates and compounds of ammonia.* 

 When sulphate of ammonia is used as a manure it 

 is reduced to nitrate before it is absorbed. The 

 nitro-bacteria of the soil transform ammonia com- 

 pounds first to nitrites and then nitrates. Most 

 plants are unable to assimilate uncombined nitrogen. 

 But peas and beans will flourish in a soil which is 

 quite free from nitrogen compounds ; their roots and 

 tubercles contain nitrifying bacteria which, in the 

 presence of a non-nitrogenous substance like glucose, 

 can form nitrogenous compounds from the nitrogen 

 of the air ; and such nitrogenous substance will be 

 absorbed, f The plants, however, only absorb 

 nitrogen in the form of ammonia and nitrates in a 

 very dilute solution, which contains molecules and 

 ions from which the plants construct nitrogenous 

 substances under the influence of the protoplasm or 

 enzymes of the cells. 



The first organic nitrogenous substances produced 

 are amino-acids, and these are the basis of the whole 

 series of protein substances. Proteins consist of 

 molecules of enormous complexity, or long chains of 



* NO' ions from certain nitrates joined with H' ions form 

 hydroxylamine, which is a base and may be regarded as ammonia 

 in which one of its hydrogen atoms has been replaced by an 

 OH ion, the formula being NH 2 (OH). Salts are formed from 

 it by direct union with acids, without elimination of water. 

 This is an example of the formation of simple nitrogen com- 

 pounds in plants. 



f Vine's " Botany." 



