272 FIRESIDE SCIENCE. 



ing stage of existence. The plant is now fairly 

 dependent for food upon its own energies, and root 

 and leaf are the theatres of great activities. 



None of the elements named as constituting the 

 food of plants exist as such in them, save oxygen 

 and nitrogen. Half the weight of a dried plant is 

 carbon, and yet it does not exist in it as free car- 

 bon ; it is all locked up in combinations of greater 

 or less complexity. There is not one of these ele- 

 ments of food that can be supplied to the plant 

 in its naked condition, as they not only have no 

 power to nourish, but are positively poisonous. 

 There is much misapprehension regarding these 

 points among ^farmers, which arises from not clearly 

 understanding the statements of writers upon the 

 chemistry of agriculture. Not unfrequently in- 

 quiries are received concerning the cost of nitro- 

 gen, carbon, phosphorus, etc., and sometimes 

 orders are sent for these agents, which are de- 

 signed to be used for fertilizing purposes. While 

 it is true Aat nitrogen is an element needful in the 

 nutrition of plants, it must be presented not alone, 

 but in one of two forms of combination, either 

 as ammonia, or nitric acid ; and further, the acid 

 must be in association with an alkali, as soda or 

 potash, in order to be safely employed by the 

 farmer. In either one of these forms, it is of im- 

 mense value as plant food. Nitrogen is a gaseous 



