The Plant Cell 19 



certain small refractive protoplasmic bodies termed 

 chromatophores. Vacuoles and food-materials of various 

 sorts may also occur as inclusions within the general 

 protoplast. 



An examination of rectangular or polyhedral cells at a 

 short distance back of the tip will reveal certain changes, 

 often denoting a passage from the formative to the non- 

 formative or adult type. In the latter the cell is larger, 

 the cytoplasm less abundant, and much of the cell-cavity 

 may become occupied by vacuoles filled with cell-sap. 

 As the vacuoles form the cell may show radiate or strand- 

 like cytoplasmic areas usually connecting the central with 

 the peripheral cytoplasm, but the nucleus may be still 

 more or less central, and is invariably imbedded in cyto- 

 plasm. As the change goes on the sap cavity enlarges and 

 all the protoplasm is drawn to the periphery, the nucleus 

 occupying the center of a marginal mass. 



The preceding defines the general type of many of the 

 living cells of the plant body not undergoing rapid growth 

 and division. In the active parenchyma of certain roots, 

 tubers, and other organs to which there has fallen the 

 office of starch or other food-stuff accumulation, the cell 

 may become packed with such products ; still, nucleus 

 and a thin layer of protoplasm remain, and these are later 

 essential in the digestion and transport of the stored food- 

 materials. 



12. Cytoplasm. - - When reference is made to the struc- 

 ture of protoplasm, it is usually the cytoplasm which is 

 considered. Fixing the attention upon the cytoplasm 

 alone, it is found that this feature of meristematic cells, 

 of germinating pollen grains, of the hyphse of black-mold 



