144 THE MOLECULAR ARCHITECTURE OF PLANT CELL WALLS 



very strongly a variation in wall structure very much as recorded above 

 for the fibrous cells. It is a most interesting and pecuUar fact that in 

 Fraxinus these "anomalous" elements are confined to relatively few 



0. 5nim. 



Fig. 53. Three contiguous elements in a vessel of Quercus alba cut open and laid out 



flat. The slit pits mark the directions of the cellulose chains. The angles (in degrees) 



to the transverse in the areas marked are as follows. A positive sign indicates an 



incline upwards to the right and a negative sign to the left. 



N.B. The contacts to ray tissue are so heavily covered with large simple pits that 

 the wall structure is completely disordered and is not therefore recorded. 



