MINUTE AN ATOM T OF FLOWERING PLANTS 215 



parent nucleus are assured to the two resulting nuclei. 

 Only after the nucleus of a cell has finished its division, 

 is the surrounding cytoplasm separated into two portions. 

 The production of two cells from one is completed by the 

 formation of a new transverse wall. 



498. Many cells possess, in addition to the nucleus, pro- 

 toplasmic organs performing special offices in the general 

 work of the cell. Cells from the interior of the leaf, for 

 example Fig. 382, contain numerous rounded or lens- 

 shaped bodies, lying in the cytoplasm near the walls. 

 These bodies, colored green by the chlorophyll pigment 

 which they contain, are the 

 chlorophyll granules or chlo- 

 roplastids. They give plants 

 their characteristic green 

 color. They are active in 

 carbon assimilation. Simi- 

 lar cell organs, with red 

 or yellow pigment instead 

 of green, give color to 

 fruits and flowers. They 

 are called chromoplastids. 



A thin external layer of 

 the cytoplasm next the cell 

 wall may be distinguished 

 by its superior clearness and 

 the absence of granulation. 

 It is very probable that this 

 really constitutes a sort of 

 membrane, possessing a closeness of structure and tenacity 

 above that of the rest of the cytoplasm. The remainder 

 of the cytoplasm is highly granular in appearance, owing 

 chiefly to the varying density of the protoplasm itself. 

 Except in their earliest stages active cells contain inter- 

 spaces, or vacuoles, filled with water and dissolved sub- 

 stances (Fig. 362). One large vacuole may fill the 

 greater part of the cell, the protoplasm forming a layer 

 next the wall. The watery contents of the vacuole or 



