PHOTO-S YNTHESIS 109 



Essential oils are the volatile constituents found in plants. 

 Turpentine oil is one of the most important. 



THE NITROGENOUS BODIES. 



The nitrates are absorbed by plants, and are subse- 

 quently converted into organic nitrogen compounds. In 

 cases of drought, plants can store nitrates in their stems. 

 All the ordinary nitrates are soluble in water. Ammonia 

 salts are only found in traces in plants. Plants, indeed, 

 cannot endure any considerable quantities of ammonia, free 

 or combined (see p. 14). 



Ammonia salts in organic materials can be distilled out 

 with precipitated chalk. 



Amides, Amines, etc. Miscellaneous non-albuminoid 

 nitrogenous bodies in plants are often called amides. A por- 

 tion of these are true amides, but some are not. Asparagine, 

 for example, is both an amide and an amino acid, which on 

 distillation with moderately strong alkali will yield half 

 its nitrogen as ammonia. Alkaloids, nitrogenous glucosides 

 and amines, are also present. 



The Albuminoids, or the Proteins, are the complex 

 bodies of which the amino acids are the basis. They can be 

 precipitated by copper hydrate, lead acetate, uranium acetate, 

 or other precipitants, the non-albuminoid nitrogenous matter 

 remaining in solution. For a rough division the nitrogen 

 insoluble in lead acetate solution may be considered protein 

 nitrogen. The ammonia distilled by potash, but not distilled 

 by calcium carbonate, can be considered as amide nitrogen. 

 The nitrogen distilled by calcium carbonate can be considered 

 as ammonia compounds, and the nitrates precipitated by 

 nitron can be taken as the nitrate nitrogen. It will not 

 infrequently be found in roots and leaves that the sum of 

 these fractions of nitrogen will not add up to the total 

 nitrogen, but in the case of grains, seeds, hay and straw, the 

 above division will not give any appreciable surplus or 

 deficiency. Roughly speaking, one may say that mature 

 plants do not contain any large quantities of nitrogen outside 



