154 THE MOLECULAR ARCHITECTURE OF PLANT CELL WALLS 



diversion into the realms of ontogeny to see how these tracheids are 

 developed. 



The development of conifer tracheids 



If a piece of bark is removed from the trunk of a conifer tree during 

 spring, and it is particularly easy to remove the bark only at this time. 



Region of shoot 

 where extension in 

 length has ceased. 



Increase in girth 

 has commenced by 

 the formation of new 

 wood elements. 



Region of shoot 

 extending in length 

 by vacuolation and 

 division of cells b. 



Fig. 54(a). Diagrammatic representation of the location of the cambium. The cells 

 are drawn many times too large for clearness of figure. 



then it will be found possible to remove from the surface of the wood a 

 thin film with the consistency of a weak jelly. Examination of this 

 under the microscope will reveal that it is actually a cellular tissue 

 consisting of rather uniform elongated cells with very thin cell walls. 



