PLANT FOOD IN THE SOIL 65 



Experiment. Crush the leaves or stems of sev- 

 eral growing plants and notice that the crushed 

 and exposed parts are moist. In a potato or an 

 apple we find a great deal of moisture. Plants then 

 are partly made of water. In fact growing plants 

 are from 65 to 95 per cent, water. 



Experiment. Expose a plant or part of a plant 

 to heat; the water is driven off and there remains 

 a dry portion. Heat the dry part to a high degree 

 and it burns ; part passes into the air as smoke and 

 part remains behind as ashes. 



We have found then the following substances in 

 plants : Woody fibre or cellulose, starch, sugar, 

 gum, fats and oils, albuminoids, water, ashes. Aside 

 from these are found certain coloring matters, cer- 

 tain acids and other matters which give taste, flavor, 

 and poisonous qualities to fruits and vegetables. 

 More or less of all these substances are found in 

 all plants. Now these are all compound substances. 

 That is, they can all be broken down into simpler 

 substances, and with the exception of the water and 

 the ashes, the plants do not take them directly from 

 the soil. 



The chemists tell us that these substances are 

 composed of certain chemical elements, some of 

 which the plant obtains from the air, some from 

 the soil and some from water. 



The following table gives the substances found 

 in plants, the elements of which they are composed, 

 and the sources from which the plants obtain them : 



