586 



THE FORMS OF TISSUES 



[CH. 



MP. Two limiting cases are to be noticed here: (1) at 90° (point 

 A in diagram), because we are at present only dealing with arcs 

 no greater than a quadrant; and (2), the point (B) where the angle 6 



Fig. 23G. 



comes to equal the angle a, for after that point the construction 

 becomes impossible, since an anticlinal bisecting partition-wall 

 would be partly outside the cell. The only partition which, after 

 that point, can possibly exist is a periclinal one; and this point, 



