76 



K I. KM FATS OF (JKNKIJAL SCIKNCK 



energy of light in manufacture of carbohydrates. If there is 

 no strong light shining upon the plant, it is not able to carry 

 on this work, and the plant factory stops. For that reason all 

 green plants must live where there is light, and they cannot 

 make starch or sugar at night. Artificial light will answer if 



it is strong enough, 

 but usually it is too 

 weak to have any ap- 

 preciable effect. 



82. Importance of 

 chlorophyll. It follows 

 from what has been 

 said in the preceding 

 sections that the carbo- 

 hydrate manufacture 

 can go on only in the 

 presence of light and 

 chlorophyll. This fact 

 causes us to regard 

 chlorophyll as a very 

 important substance. 

 All plants which have 

 chlorophyll are able to 

 manufacture their own 

 food, while plants which 

 do not (figs. 40 and 41) 

 have it are obliged to 

 depend upon securing 

 the food already made. 

 We may call those plants which have chlorophyll independent 

 plants, and those which do not have it dependent plants. 



83. Photosynthesis. The process in which the chloroplasts 

 of green plants, with the aid of light, manufacture carbohy- 

 drates out of water and carbon dioxide, is called photosynthesis. 

 This is the name for the process we have been studying. 



FIG. 40. Indian pipe, a dependent plant 



The plant is wholly without chlorophyll. It se- 

 cures its food from organic substances in the soil 



