844 INTRODUCTION TO BOTANY 
C,H,,0,, and in making this unit of starch there has been used 
all of the carbon, all of the hydrogen, and five units of the 
oxygen, thus leaving twelve units of oxygen to be set free or 
to be used by the plant in some other way. Some of this free 
oxygen passes into the air, though some of it is used by the 
plant in a later process. 
‘The compounds thus constructed, such as starch and sugar, 
are called carbohydrates, the name indicating that they are 
compounds of carbon and water. 
