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 alge, and also the similar 
ones often found in young leavés, 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 
