THE CELL. 



15 



ever, the same uncertainty still surrounds " heredity " as it does the 

 "idioplasm " of Kiigeli. 



A process directly opposite to that of nuclear division is the 

 union of nuclei. This process evidently plays a part, though un- 

 explained, in reproduction, in the fertilization of one cell by another. 

 (See chapter on Reproduction.) 



{h) Chlorophyll Grains, Chromoplastids^ Leucoplastids. 



These three structures are, as has been indicated, included under the 

 name chromatophores. A discussion of chlorophyll bodies will lead 

 to the discussion of chromoplastids and leucoplastids. 



In all chlorophyll bodies there is a green coloring matter, 

 chlorophyll. It is intimately associated with the highly important 

 function of carbon assimilation, which will be discussed later. Even 

 in the carbon-assimilating plants of a red-brown or blue-green 

 color (as for example red and brown marine algae) it is assumed 



Fig. 3. (After Sachs.) Fig. 4. — A portion of prismatic cell 



with lateral chlorophyll - bodies 

 (schematic). 



Optical cross-section at q: surface view 

 at/; optical longitudinal section at I. 



that they contain active chlorophyll, but that it is hidden by some 

 other coloring matter. Among vascular plants there are also nu- 

 merous instances where the chlorophyll-bearing cells are colored red 

 by the cell-sap. Among phanerogams, vascular cryptogams, and 

 mosses the chlorophyll bodies are disk-shaped, though usually 

 spoken of as " chlorophyll grains." These disks lie with the flat 



