IX] PROTOPLASMIC CELL-CONTENTS 93 



clashing together of atoms in course of reconstruction into 

 new groupings. That his experiences would be varied, 

 and periodically violent on the scale presupposed we 

 may be sure, and although to our senses all these pro- 

 found changes going on in the cells of a green leaf waving 

 in the sunshine appear to be proceeding continuously and 

 quietly, a little reflection must convince us that restful- 

 ness is the last attribute we can attach to machinery that 

 is doing and undoing so much : setting free energy here 

 and locking it up there, in forms that must mean powerful 

 disturbances of the matter involved. 



Let us now look somewhat more closely at the con- 

 tents of the mesophyll-celk These are principally the cell- 

 protoplasm {cytoplasm) lining the interior of the cell-wall, 

 and enclosing in its substance the chlorophyll -corpuscles, 

 the nucleus and other bodies ; and the cell-sap occupying 

 the interior of the cell as a large vacuole, which the proto- 

 plasm envelopes and in which it is bathed. 



All we need say here regarding the protoplasm is that 

 it regulates the movements and constitution of all the 

 other parts. It is in life continually undergoing changes, 

 and the granules in its substance can be seen in move- 

 ment : it is the living substance of the cell. All salts, 

 organic materials, and so forth, however soluble in water, 

 can only pass in and out of the cell through the proto- 

 plasm, and it is the protoplasm alone which regulates the 

 supplies of watery solutions that can pass through the 

 cell-membrane. This is easily seen on killing the proto- 

 plasm. Solutions held fast in the cell-sap so long as 

 the protoplasm was alive held so fast that the state of 

 distension referred to as turgidity was possible pass out 

 at once as through a mere piece of muslin, when the 

 restraining protoplasm is killed ; and poisons, coloured 

 solutions, or anything which can traverse the mere cell- 



