SOME COMMON BOTANICAL ERRORS 151 



carbon dioxide. But it happens that green plants have 

 an additional power, utterly lacking in animals, to form 

 their food from certain gases, minerals, and water, and 

 in this process (photosynthesis, or assimilation) carbon 

 dioxide is absorbed and oxygen is given off. In green 

 plants, in bright light, this process is so very much 

 more active than the process of respiration, that the 

 plant as a whole does give off much more oxygen than 

 carbon dioxide, but in darkness the food-making stops, 

 and the plant then gives off carbon dioxide precisely as 

 animals do. It is therefore only in virtue of their 

 possession of this single extra power that plants reverse 

 the process of animals ; in nearly all others of their 

 important vital actions they behave like them. 



Much misunderstood is the nature of plant food. It 

 is generally taught that plant food consists of carbon 

 dioxide, minerals, and water. If by food one means 

 anything taken into the organism, this is correct ; but 

 if by that term one means the substance out of which 

 the organism builds up new tissues, repairs waste, and 

 obtains energy for its own vital work, then this is in- 

 correct. In reality the plant has the power, lacking in 

 animals, of absorbing the carbon dioxicfe, water, and 

 minerals, and of making from these starch or a related 

 substance ; and this starch is then used as food in 

 essentially the same manner as animals use it. It may 

 be said, then, that plants form their food from the raw 

 materials, which properly are not food at all. Of 



