104 THE MOLECULAR ARCHITECTURE OF PLANT CELL WALLS 



is cut open, laid out flat and dried, then the diagram resulting with the 

 X-ray beam normal to the surface is indistinguishable from that of 

 Valonia (Plate IV, Fig. 1). The wall of this species also, therefore, 

 consists of two sets of cellulose chains crossing each other almost at 

 right angles. Here again, too, two sets of striations are visible on the 

 wall— and this is true of most species— which correspond in direction 



61A 

 C'54A-fj^ 



39A 



^t03A 



/' 



IO-3A 



54A 



(a) 



(b) 



Fig. 37(a) The mutual orientation of the unit cells of cellulose corresponding to the 

 directions of cellulose chains in cells towards the apex of Cladophora. 



Upper half, arrangement corresponding to longitudinal chains. 

 Lower half, arrangement corresponding to transverse chains. 



Fig. 37(/>). Diagrammatic representation of the corresponding X-ray photograph, 

 with the beam perpendicular to cell length. The lettering of the 61 and 5-4 A arcs 

 denotes the positions in Fig. 37(a) from which the arcs are derived. Note that the 

 equatorial 5-4 A. arc arises from longitudinal chains and the meridional arc from the 

 transverse, while the equatorial 61 arc is "mixed". 



to those of the cellulose chains. It seems therefore very reasonable to 

 assume that the organization of the wall is very similar to that obtaining 

 in Valonia. Towards the tip of the filaments of mature plants in fact, 

 the striations, of which more will be said later, run one set in a slow 

 spiral and the other in a very steep spiral, i.e. almost parallel and 

 perpendicular to cell length. The organization of a whole cell of the 

 filament (ignoring the end walls) must therefore be somewhat as in 

 Fig. 37(a). This can be checked against the X-ray diagram, Plate IV, 

 Fig. 4 and Fig. 37(6). Taking the arcs corresponding to planes of 6T A. 



