22 EVOLUTION OF PLANTS 



bon dioxide and water is accomplished, and from their 

 elements are manufactured the organic carbon com- 

 pounds. When these green cells are exposed to the 

 light, starch can soon be detected in them, but it dis- 

 appears if the plant is placed for a short time in dark- 

 ness. 



The presence of other pigments, such as the red and 

 yellow ones in the marine algse, and also the similar 

 ones often found in young leaves, doubtless advan- 

 tageously modify the light which passes through them 

 before reaching the chlorophyll. 



Movement is not generally associated with one's idea 

 of a plant, but it is a property which all plants possess 

 to some degree, and is usually associated with the 

 sensitiveness of living protoplasm within the cells. 

 In every living cell the protoplasm shows more or 

 less marked movements which may not be at once 

 perceptible, but sometimes are very active indeed. 

 These movements are very familiar to botanists in the 

 cells of many water plants, e.g. the eel-grass (Vallis- 

 neria) and stone-wort (Chara), and are also very active 

 in the cells forming the hairs upon the surface of many 

 land plants. This is especially true of the hairs upon 

 various parts of many flowers. 



Spontaneous movements of the plant as a whole 

 are confined to a comparatively small number of low 

 aquatic forms (see Fig. 6). Here the plant moves by 

 means of vibratile protoplasmic threads or cilia, which 

 propel it through the water, precisely as many of the 

 lower animals move. The extraordinary resemblance 

 between these low ciliated plants and the lower animals 

 is one of the strongest evidences of the relationship 



