CHAPTER I. — THE CELL. 



*33 



protoplasm and to matters of similar chemical nature which do 

 not exhibit vital phenomena. 



Ordinary protoplasm is formless ; even when viewed under 

 the highest powers of the microscope, it exhibits no evident 

 structure beyond that already described, except the presence of 

 great numbers of very minute granular bodies called microsomes, 

 the nature and uses of which are not yet understood. It passes, 

 however, into several modifications which exhibit a more or less 

 characteristic structure. Among the most important of these are 

 chlorophyll bodies. These are the proteid corpuscles that contain 

 the green matter, chlorophyll, to which 

 leaves and other green parts of plants 

 owe their color. They are commonly 

 rounded, oblong, or somewhat flat- 

 tened, but sometimes take the form 

 of spiral bands, as in the cells of Spir- 

 ogyra, or of stellate masses, as in the 

 cells of Zygnema, Figs. 372 and 373. 

 Occasionally, also, they are found in 

 other shapes. In a few instances, as in 

 some green Protophytes, there are no 

 chlorophyll bodies, but the green col- rt 

 oring matter is diffused through the 

 unmodified protoplasm. fig. 372. 



Fig. 372.— Two cells from Zygnema, a filamentous fresh water alga, showing stellate 

 arrangement of chlorophyll. Magnified about four hundred diameters. 



Fig. 373- Two cells from Spirogyra, a filamentous fresh water alga, showing spiral 

 chlorophyll bands. Magnified about five hundred diameters. 



Chlorophyll bodies are observed to contain in daylight minute 

 starch grains, which at night dissolve and disappear. If a green 

 plant be kept in darkness, no starch is found, and gradually the 

 green color fades out of the chlorophyll bodies, and they become 

 colorless or yellowish, and the plant consequently appears as if 

 bleached. 



In some plants, for example, the Red Marine Algae and the 

 Diatoms, other coloring matters dissolved in the cell-sap obscure 

 or greatly modify the proper color of the chlorophyll. 



The colors of many flowers and fruits are due to other proteid 

 bodies of a similar character, which, however, contain a different 

 coloring matter. These are called chromoplasts. See Fig. 374. 



