Plant Substance 27 



substances in plant and animal bodies. Nitrogen is 

 always present in the living substance, or protoplasm. 

 The other elements, usually called the " mineral ele- 

 ments," while absolutely essential, occur only in small 

 amounts, usually less than five per cent. These elements 

 form the "ash," when plants are burned.. 



QUESTIONS 



1. Name some of the reserve food substances. 2. What is 

 meant by a "chemical element"? Name some common ones. 3. Do 

 plants contain simple elements? Name three plant materials that 

 contain the same elements combined differently. 4. By what 

 means does the plant manufacture complex compounds out of 

 simple compounds? 5. Name the elements essential for plant 

 growth. 6. Name the most common non-essential elements in 

 plants 7. What are the proportions of the elements in plants? 



