284 



CELI^DIVISION 



diameter of a spherical cell would multiply its area four 

 times (i.e., the square of 2) and its volume eight times 

 (i.e., the cube of 2). The result would be that the volume 

 or amount of protoplasm to be supplied through the sur- 

 face of the cell would have increased twice as much as the 

 surface through which it is to be supplied. Clearly, fur- 

 ther increases in size would finally reach a point where 

 the volume of protoplasm in the cell could not be sup- 



Fig. 65. — The Comparative Surfaces of Solids, The edge of the 

 larger solid is 2 in. on each side. It therefore contains 8 cu. in. Each 

 side is 2x2 in. and hence 4 sq. in. in area. The whole area is thus 

 24 sq. in. A cube of 1 in. on the side, as e.g., the one in the upper 

 right corner of the larger one, o, B, c, rf, e, /, g, /», contains 1 cu. in. 

 and has a Hurface of 6 sq. in. From these figures it is clear that 

 doubling the side increases the area 4 times but at the Siime time 

 increases the solid contents 8 times. In other words the contents in- 

 crease twice as fast as the area. Although not quite so obvious this 

 fact is equally true of a sphere or any other shape of solid. 



plied through its surface in an adequate manner. It is 

 not improbable that this state of affairs may act as the 

 stimulus to division. Plant cells usually meet this situa- 

 tion by forming a large vacuole which reduces the 

 volume of protoplasm accordingly. As we should expect 

 from this fact, plant cells are on the average larger than 

 those of animals. 



