INVESTIGATION OF STRUCTURE IN PLANT CELL WALLS 



33 



again it may be chosen rather than any other solely on the grounds 

 of simplicity. Such a body is called a unit cell. 



Before proceeding to consider the methods by which these parameters 

 can be determined and to observe the conclusions which can then be 



•a 



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a 



O- 



E 



3 

 O 

 / 





F 



ilV?. 



o 



o 



,8....-., 



D 

 O 



y 



G 



O 

 H 



O 



O 



o 



o 



o 



{h) 



o 



-o- 



o 



-o- o u -p 



M N ^/; 

 o o -p: 



/ ■ / 



I 



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-(s--^^----(> ---9- -o-----p-ri 

 p--fo---/-o- --/-<)/ 



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(c) 



Fig. 10. For explanation see text. 



drawn, it will be profitable to consider some other features associated 

 with this regular repetition of points in space. Returning for the 

 moment to the two-dimensional lattice (Fig. 10(b)), it will be noticed 

 that not only do the points lie along the lines by which their position 

 was defined above, but they lie also along other lines such as IB, JC, 

 KD, etc. (Fig. 11); in fact each point is the meeting-place of an infinite 

 number of different hnes all running through these points. Suppose it 

 is necessary to define any one of these sets of parallel lines in terms of 



3 



