32*2 CONSERVATIVE ORGANS. [LECT. VII. 



the microscope, is seen to consist of two distinct 

 parts, both cellular, but nevertheless different. 

 The exterior, or that on which the cuticle imme- 

 diately reposes, appears to be composed of a dark 

 green, semiorganized pulp, in which the cells are 

 irregular both in their dimensions and form (vide 

 Plate 6, fig. 2, 6.), and has somewhat of the as- 

 pect, as Mr. Keith aptly expresses himself, of " a 

 " distinct and separate epidermis in an incipient 

 " state, rather than a true and proper pulp :" 

 while the interior is less coloured and composed 

 of regular hexagonal cells (Plate 6, fig. 2, c.), 

 the sides of which are perforated and frequently 

 studded with small granular bodies. It is the ex- 

 terior layer of the cellular integument, which is 

 the seat of colour of the young twig, and the 

 green hue of which is transmitted through the 

 yet semitransparent cuticle : its appearance, and 

 the fact that it is annually reproduced, led Mr. 

 Keith to believe that it is really the next year's 

 cuticle in an incipient stage of organization. But 

 the vertical direction of the cells, while those of 

 the cuticle are horizontal, is sufficient to overturn 

 this opinion, (Plate 6, fig. 7, a. I. 2.) These two 

 portions of the cellular integument are particu- 

 larly noticed by Mirbel, who denominates the 

 exterior the herbaceous tissue, and the interior 

 the parenchyma ; and conceives, with much pro- 

 bability, that the deeper green colour of the latter 



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