NITROGEN AND AMMONIA. 47 



very acid in cold summers, while in the tropics the most numerous 

 trees are those producing oils, caoutchouc, etc., which contain little 

 oxygen. Thus the effects of heat are particularly noticeable upon 

 fruit, both in its nature and quality. The resins of leaves diminish 

 and oxygen is absorbed by ripening fruits in the dark ; coloring 

 matters are formed, and some of the acids replace sugar, starch, or 

 gum. 



Nitrogen in plants forms an important part, as well also as in rich 

 vegetable moulds. Rain and snow are supposed to be the means by 

 which plants are supplied with this element, through the ammonia in 

 the atmosphere brought to the earth by them. Ammonia is a gas 

 composed of 1 vol. of nitrogen to 3 of hydrogen. This is the fruitful 

 source of nitrogen in temperate climates and nitric acid in tropical 

 climates ; but the formation of the latter is a product of the former. 

 Ammonia is considered the last product of animal putrefaction, and 

 nitric acid is the result of the transformation of ammonia. A genera- 

 tion of 1000 millions of men, with as many of lower animals dying 

 annually, is considered an adequate source for all the ammonia and 

 nitrogen required for vegetation. Its presence in rain water may be 

 detected by adding a little sulphuric acid to it and evaporating it to 

 dryness in a porcelain basin. The ammonia remaining with the acid 

 is detected by a little powdered lime. The sensation of softness in 

 rain water is owing to carbonate of ammonia. A portion of the nitrogen 

 thus contained in ammonia is taken up by the roots and produces cer- 

 tain qualities in plants in which it is found, as albumen, gluten, 

 quinine, morphia, etc. Every part of vegetables contains ammonia; 

 the root, as the beet, the tree stem, as maple, and in all blossoms and 

 unripe fruit. In the form of urine it is one of the most useful manures. 

 Ammonia forms the red and blue coloring matter of flowers. The 

 quantity of food which men or other animals eat is increased or 

 diminished in proportion to the substances containing nitrogen. 

 Nitrogen is believed to constitute one-hundreth part of the weight of 

 grass. Certain soils absorb ammonia from the air, and thus obtain 

 nitrogen. Humus, or decayed wood, affords a considerable quantity of 

 ammonia. 



The inorganic constituents of plants are derived from acids and 

 alkalies, and these form neutral compounds, or salts, of various and 

 important qualities in vegetation. Phosphate of magnesia is an in- 

 variable constituent of the seeds of all grasses and is introduced into 

 bread and also into beer. Most plants contain organic acids, all of 

 which are in combination with bases, as potash, soda, lime, or mag. 

 nesia. These are in the greatest quantities in the organs which pre- 

 pare substances for the food of plants ; in the leaves more than the 

 branches and in these more than in the stem. As all plants yield ashes 

 containing carbonic acid, all must contain the salts of an acid in the 



