158 THE MOLECULAR ARCHITECTURE OF PLANT CELL WALLS 



wood are shorter than those in outer rings, and there is normally a 

 progressive increase in tracheid length from inner to outer rings. 



This gives us a ready means of settling the possibility of a connection 

 between cell length and wall structure in these cells. 



Variation of spiral angle with tracheid length 



The earlier investigation consisted of a series of measurements of the 

 m.e.p. of tracheids taken from various annual rings at the same level 

 in a variety of conifer trees, the determinations being made using the 



Fig. 55. Graphical representation of the variation of the average spiral angle 



across the annual rings in Cedms. 



-O- 



tangential walls, 

 radial walls. 



The angle given is that between the m.e.p. and cell length. 



technique described in the last chapter (p. 116). Parallel with this, a 

 series of length measurements were made on comparable pieces of wood 

 so that the average tracheid length and the average spiral angle was 

 available for each annual ring. In view of the above description of the 

 development of tracheids, it will be clear that radial and tangential 

 walls had to be considered separately and this separation is maintained 

 in Fig. 55 and Table XIII, where a representative set of data is provided. 

 It is abundantly clear that the relation between cell length and spiral 

 angle is of the type expected. At the time this work was pubhshed, it 

 was thought that the m.e.p. referred to the whole wall thickness, but 



