PHYSIOLOGY. 103 



The following table, after Sachs,* indicates the 

 action of light on vegetation : 



A. GENERAL. 



(1) Action of rays of different refrangibility. 



(2) Variation in the action of light on plants in proportion to its 



intensity. 



(3) Penetration of the rays of light into the plant. 



B. SPECIAL. 



(1) Chemical action of light on plants, 

 (a) Formation of chlorophyll. 



(6) The decomposition of carbon dioxide. 



(c) Formation of starch in the chlorophyll. 



(2) Mechanical action of light on plants. 



(d) The influence of light on the movements of protoplasm. 



(e) Cell division and growth. 



(/) Action of light on the tension of the tissue of the con- 

 tractile organs of leaves endowed with motion. 



Light may retard the growth of cells, as in 

 heliotropism. 



Darwin f has demonstrated many facts concern- 

 ing the action of light on plants. 



* Sachs, " Text-book of Botany." 

 t " Movements of Plants." 



