160 THE LOWEST ORGANISMS AND THE CELL 



Second. The protoplasm of green portions of plants will be 



found to contain green bodies called chromatophores (meaning 



color bearers). Chromatophores have a great variety of forms in 



different plants and are sometimes very complex and beautiful, 



-as the spiral band in the cells of the pond scum, Spirogyra 



(Fig. 168, A). The green color- 

 ing matter in a chromatophore 

 is called chlorophyll (meaning 

 leaf green). Green chromato- 

 phores are called chloroplasts 

 when small and numerous in 

 a cell. Chloroplasts are char- 

 acteristic of the cells in plants 

 above the thallophytes, and 

 may be readily studied in the 

 leaves of mosses (Fig. 169, A), 



ferns, and seed plants. Chro- 

 matophores are sometimes col- 

 ored brown or red, as in the 

 cells of the brown and the red 



FIG. 168. Cell structure of the pond 



~&i 



scum (Spirogyra) 



algse. Chromatophores are 

 J, living cell, showing spiral hand-like peculiar to plants, never being 



chromatophore with pyrenoids p, and found iu typ j ca l an i ma l cells. 



centrally placed nucleus n; 1>, living 



cell after treatment with a salt solu- The protoplasm of the plant 



tion, the protoplasm contracted away cell a l ways li es directly Under 



from the cell wall ; C , pyrenoid stained 



with iodine and very greatly magni- the cell wall, Sometimes COin- 



fied (about 1000 diameters), a circle of ]etel fim i]}Q cavit bufc 



starch grains around the pyrenoid 



more frequently forming a lin- 

 ing which surrounds one or more spaces, or vacuoles, which 

 contain a watery fluid called cell sap. The relation of the proto- 

 plasm to the cell wall is easily understood when the protoplasm 

 is made to contract from the wall by the withdrawal of the 



/ 



watery cell sap from the vacuoles. Thus if a filament of a pond 

 scum or a portion of a moss leaf be placed in an aqueous solu- 

 tion of common salt (5 or 10 per cent), the cell sap is drawn 



