52 Report of the Acting Director and Chemist of the 



cultivable soils, and hence does not need to be considered in con- 

 nection with commercial fertilizers. 



4. The Specific Action of Different Elements of Plant-Food 



UPON Plants. 



The quet-tion is often asked in cunnection with the different con- 

 stituents of plant-food regarding the function each performs in 

 plant growth. It is well known that each element contributes to the 

 building of definite compounds contained in the plant, and that each 

 has one or more special offices to fulfill. While the specific action 

 and functions of the different elements are not clearly understood 

 in all details, much is known, and we now present a brief outline of 

 the facts relating to this subject, so far as known. 



Carbon is a constituent of nearly all the compounds, except 

 water, found in plants, such as starch, fibre, sugar, fat or oil, 

 albuminoids, acids, etc. Hence, its function is to supply its necessary 

 part of the material found in such compounds. The carbon dioxide 

 is taken into the leaves of plants, and in the presence of sunshine is 

 decomposed, its carbon uniting with other elements to form various 

 compounds, its oxygen being largely returned to the air. 



Oxygen, next to carbon, is the most abundant element found in 

 plants, and there are very few compounds occurring in plants which 

 do not contain more or less oxygen. The chief function of oxygen 

 is to supply the various compounds of plants with the needed por- 

 tion of this material. Plants require oxygen about as much as do 

 animals. Green plants can not flourish without a supply of oxygen. 

 The absence of oxygen prevents the germination of seeds. Con- 

 siderable quantities of oxygen are absorbed from the air by the 

 opening buds of trees. More or less oxygen in the soil is necessary 

 for the active life of roots. In the act of flowering, the absorption 

 and chemical action of oxygen in the blossom is so marked, in some 

 cases, as to develop sufficient heat to be measured by a thermometer. 



Water (Hydrogen and Oxygen). — In the combination of oxygen 

 with hydrogen in the form of water, these two elements perform 

 important functions. In the flrst place, nearly all the hydrogen 

 found in the different compounds of plants comes from water. 

 More or less of the oxygen is also supplied this way. In addition 

 to furnishing materials with which to build other compounds, water 

 acts as a carrier within the plant in transferring from one part of 

 the plant to another, as needed, the various products contained in 



