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 

 algae. Chromatophores are 

 peculiar to plants, never being 

 found in typical animal cells. 

 The protoplasm of the plant 



FIG. 168. Cell structure of the pond 

 scum (Spirogyra) 



A, living cell, showing spiral hand-like 

 chromatophore with pyrenoids p, and 

 centrally placed nucleus n ; B, living 

 cell after treatment with a salt solu- 

 tion, the protoplasm contracted away cell a l ways lj es directlv Under 

 from the cell wall ; C, pyrenoid stained * . ' 



with iodine and very greatly magni- the Cell wall, sometimes COm- 

 fied (about 1000 diameters), a circle of lefcel fiuin the cayit but 

 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 



