160 THE LOWEST ORGANISMS AND THE CELL 



Second. The protoplasm of green portions of plants will be 



found to contain green bodies called chromatopliores (meaning 



color bearers). Chromatopliores 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- 

 pliores 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- 

 matopliores are sometimes col- 

 ored brown or red, as in the 

 cells of the brown and the red 



algae. Chromatophores are 



FIG. 168. Cell structure of the pond 

 scum (Spirogyra) 



A, living cell, showing spiral band-like peculiar to plants, never being 



chromatophore with pyrenoids p, and found in typical animal cells . 



centrally placed nucleus n; fi, living 



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



tion, the protoplasm contracted away U alw H directly Under 



from the cell wall ; C, pyrenoid stained J J 



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



fied (ahout 1000 diameters), a circle of ^Ipfplv fillino- thp ravirv hnf- 



starch grains around the pyrenoid ? i cavity, but 



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 



