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THE LIFE OF THE PLANT 



the cell as such may vary widely in structure ; it is 

 either uniform and thin (as in fig. 42, i and 2), or 

 thickened everywhere in concentric layers (fig. 42, 3 and 

 5) ; or, lastly, these inner layers may not be uniformly 

 deposited on the cell-wall, but only at certain places, 



FIG. 42. 



thus forming the most curious patterns. For instance, 

 if only small parts of the cell-wall remain unthickened, 

 the cell as a whole instead of being uniformly transparent 

 will appear spotted, and in transverse section will be 

 found canals perforating the thickness of the cell-wall 

 and corresponding to these spots (fig. 42, i and 3). It is 



