THE FORM OF THE PLANT CELL 



15 



membrane separating two protoplasts consists of three layers — the 

 primary wall of each cell together with the cementing material, 

 middle lamella, between. These three layers together are so thin that 

 measurement becomes very inaccurate and it is therefore somewhat 

 difficult to tell precisely what is happening. Chemical analysis, which 



-14 



>I2 



■10 



•8 



•6 



■4 



•2 



Wal weight 

 per coleoptile 

 (xlO^) 



>' 



- 4- 



--© 



Length 



Fig. 3(a). The relation between wall weight per coleoptile (gm. x 10*) and coleoptile 

 length (cm.) during elongation by vacuolation. Weight in gm. ( x 10*) (Preston 



and Clarke). 



- — crop in light at 23 ° C. 

 -•— crop in light at 20° C. 

 -♦— crop in light at 30° C. 



+ crop in dark at 10° C. 

 ♦ crop in dark at 23° C. 

 ® crop in dark at 30° C. 



Note that the wall weight increases over the whole growth period. The pronounced 



upward curve after four days in the crop grown in light at 23° C. is associated with 



a cessation of growth in length at the end of four days under these conditions. 



would give the answer, is commonly rather difficult to carry out on 

 account of the difficulty in culturing a tissue of exactly equivalent cells 

 going through the same stages of development simultaneously, but this 

 can partially be achieved with coleoptiles. These are tubular organs 



