Plant Substance 25 



plants. They find that every plant contains a variety 

 of substances, though the quantity and' number vary 

 in different kinds of plants. Some plants, as corn, con- 

 tain much starch in their seeds, and but little in the 

 stalk. Some plants have a large amount of sugar, as 

 beets and sugar-cane, while others contain oil. These 

 substances which we call starch, oils, sugars, proteids, 

 resins, gums, acids, etc., are themselves compounds 

 of a number of " elements." The carbon mentioned in 

 H 29 is an element. So are iron, sulphur, lead and the 

 oxygen of the air. 



40. Compounds of Elements. A simple element is a 

 substance of a peculiar kind that cannot be reduced by 

 analysis to any simpler state. When wood burns, the 

 carbon (an element) of the wood combines with the 

 oxygen (an element) of the air, to form an invisible 

 gas, known as carbon dioxid (a compound). When iron 

 " rusts," it has formed a compound with the oxygen 

 of the air. In germinating seeds, the oxygen absorbed 

 is afterward given off as carbon dioxid. Oxygen com- 

 bines with another element which we call hydrogen, 

 to form the substance we call water. Thus we see that 

 the same element may combine with a number of other 

 elements, making a different compound or substance 

 with each combination. 



41. Substances Found in Plants are usually complex 

 compounds of the simple elements; for instance, staich 

 is a combination of carbon, oxygen and hydrogen, 

 and the properties of the substance we call starch are 

 different from any of its parts. Sugar is composed of 

 these same elements, but has them combined in a 

 different way. Wood is composed of the same three 

 elements, yet combined in still a different way. 



