THE ALGAE 



57 



When food and oxygen are plentiful the organism swims actively about 

 by means of its flagella which, by their rapid circular motion, act as tractor 



EYE SPOT- 

 NUCLEUS 



VOLUTIN 

 GRAINS 



APICAL PAPILLA 



BASAL GRANULES 

 CONTRACTILE VACUOLE 

 — CELL WALL 



OUTER CYTOPLASM 

 CHLOROPLAST 

 INNER CYTOPLASM 

 PYRENOID 

 STARCH 



Fig. 31. — Chlamydomonas. Diagram showing the 

 complete structure of the vegetative cell. (After 

 Pascher.) 



propellers, drawing the organism along at a good speed, flagella foremost, 

 with a spiral movement. 



The water and inorganic salts required for life are absorbed over the 

 whole surface of the cell. The water contains dissolved carbon dioxide 

 which, in the presence of light and chlorophyll, is combined with water to 

 form sugar and starch. The starch is formed as little grains, clustered round 

 the pyrenoid. The cell is attracted towards light of moderate intensity, the 

 response being apparently due to the sensitiveness to light of a tiny spot of 

 red carotinoid pigment at the forward edge of the chloroplast. This eye 

 spot or stigma is covered by a minute lens in the thickness of the cell wall 

 and is supposed to function as an extremely primitive eye. 

 3 A 



