82 



Growth 



plastic" growth, a rather vague concept that there is a readjustment 

 of all the cell walls operating in one "common framework" and with 

 no slipping between adjacent ones. Sinnott and Bloch ( 1939, 1941 ) studied 

 living and growing tissues of young roots where the gliding of one 

 cell past another would be recognized, if it occurred, by alterations in 

 relative wall positions and found no evidence for it. They suggested 



Xylem 



o 



Cambium 



330u 



3IOii 



365ii 



Fig. 4-20. Origin of ray initials in gym- 

 nosperms. Radial sections from Thuja, 

 showing progressive subdivisions of fusi- 

 form initials and the consequent origin 

 of several ray initials. (From Barman.) 



that changes in intercellular relationships come about by intrusive growth 

 limited to a particular region (such as the tips of cambial cells), so 

 that the cell may grow in between its neighbors without requiring that 

 it slide past them. Bannan and Whalley (1950) have shown how this 

 is accomplished in elongating fusiform initials. Schoch-Bodner and Huber 

 ( 1951 ) present evidence that the phloem fibers of flax, which become very 



