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pith, since the roots of dycotyledonous 

 plants, (plants whose seeds have two coty- 

 ledons, — I know of no easier language,) 

 which may be said to grow by juxta- 

 position, have no pith ? In their stems and 

 branches, which grow in diameter in the 

 same way, the pith is supposed to be dead 

 and functionless ; but in the shoot of the 

 current year, which may be said to grow 

 by intus-susception, the pith is a most 

 prominent feature, and apparently full 

 of vitality and vigour, and the woody 

 monocotyledonous stem (the palm, the 

 yucca, &c.), whose growth in diameter 

 is entirely and permanently by intus- 

 susception, may be called one entire and 

 permanent column of pith. 



Duhamel thought that the last year's 

 layer of bark was converted into the this 

 year's layer of wood. We can see that this is 

 not the case. Du Petit-Thouars thinks that 

 the new layer of wood is formed by the buds 

 (though I believe the origin of this theory 



c 2 



