INCOME OF THE PLANT. 



147 



bodies or chromatophores / for plants which, like fungi, etc., are 

 devoid of chlorophyll are unable thus to acquire energy. Enter- 

 ing the chlorophyll-bodies, the kinetic energy of sunlight is ap- 

 plied to the decomposition of carbon dioxide (CO 2 ) and water 

 (1I 2 O). After passing through manifold but imperfectly known 

 processes, the elements of. these substances finally reappear as 

 starch (C 6 H 10 O 6 ) often in the form of granules imbedded in the 

 chlorophyll-bodies, and free oxygen, most of which is returned 



INCOME OF PTERIS. 



to the atmosphere. Thus the leaf of Pteris in the light is con- 

 tinually absorbing carbon dioxide and giving forth free oxygen. 



Carbon dioxide and water contain no potential energy, since 

 the affinities of their constituent elements are completely sat- 

 isfied. Starch, however, contains potential energy, since the 

 molecule is relatively unstable, i.e., capable of decomposition 

 into simpler, stabler molecules in which stronger affinities are 



* It lias been generally believed that plants are unable to make use of free 

 atmospheric nitrogen, but recent investigations have disproved this view for 

 certain species. 



