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. 



NOTE. It is important that students should have a reason- 

 ably clear notion of the properties of matter, what an element is, 

 and the differences between a mixture, a solution, and a chemical 

 compound. Some simple experiments will prove very helpful in this 

 connection, such as the burning of a match, a lamp, or a sulphur or 

 tallow candle, with a discussion and explanation of the phenomena 

 in each case. Likewise, experiments involving the dissolving of salt 

 or sugar in water, and its subsequent recovery by the evaporation 

 of the water, should be performed and discussed fully. 



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? 



