XIII. THE PLANT 



THE plant is a living being, usually with many parts, called 

 organs, which it utilizes for taking in nourishment, for breathing, 

 for protection, and for reproduction. Every plant of the higher 

 orders has three kinds of organs; namely, the 

 root, the stem, and the leaf. The growth of the 

 root is downward in the soil towards darkness 

 and dampness, while that of the stem is up- 

 ward towards light and air. The stem is the 

 axis of the plant, and it is the part which bears 

 all the other organs. The stem is the channel 

 through which food prepared in the leaves 

 passes to the roots. 



The leaves in some respects correspond to 

 the lungs in human beings, and through them 

 the functions of respiration and transpiration 

 are effected for the plant. In the air there 

 is always present a certain amount of carbon 



j- -j j T. -^ xu 



dioxide, and when it comes in contact with the 

 plant a portion of the carbon is taken up by the leaves, and the 

 oxygen is left free in the atmosphere to be used by animals. 

 They in turn contribute their share of carbon dioxide for the use 

 of the plants. 



Besides this a great deal of carbon is returned to the air in the 

 form of gas from fuels of different kinds while in a burning state. 

 Millions upon millions of pounds of carbon are given back to the 

 air every day by the numerous factories scattered all over the 

 world. All the carbon in the plant comes from the carbon dioxide 

 in the air. None comes through the roots from the soil. Carbon 

 dioxide is taken up only by green plants and only in the presence of 

 sunshine or other strong light. Carbon dioxide and water after 

 coming in contact with the chlorophyll, or green substance, in the 

 leaves are transformed into starch and sugar and other foods 



63 



Seedlings of 



