258 THE ANATOMY OF STEMS. 



mulation of such layers forms the rugged surfaces ol 

 stems, as we see in the Elm, the Oak, and the ma- 

 jority of trees. In the greater number of instances it 

 cracks vertically, and is pushed outwards with a por- 

 tion of the cellular integument by the new epidermis, 

 which can be brought into view by removing these 

 rugged portions. In others it splits horizontally, and 

 the new cuticle is formed immediately under the old, 

 which, after a time, detaches itself in fragments ; or, 

 there is a succession of cuticles, which, although one 

 is formed every year, do not separate annually, but 

 occasionally only, in multiplied layers, that can, how- 

 ever, be readily detached from each other, as in the 

 the Currant and the Paper Birch. 



2. The Cellular integument. On carefully raising 

 the cuticle of the young shoot of the Horse Chesnut, 

 we find under it a cellular layer ; which, in a trans- 

 verse section of the stem placed under the microscope, 

 is seen to consist of two distinct parts, both cellular, 

 but nevertheless different. The exterior, or that on 

 which the cuticle immediately reposes, appears to be 

 composed of a dark green, semi-organized pulp, in 

 which the cells are irregular both in their dimensions 

 and form, and has somewhat of the aspect, as Mr. 

 Keith remarks, of " a distinct and separate epidermis 

 in an incipient state, rather than a true and proper 

 pulp ;" while the interior is less colored and compos- 

 ed of regular hexagonal cells, the sides of which are 

 perforated and frequently studded with small granu- 

 lar bodies. It is the exterior layer of the cellular in- 

 tegument, which is the seat of color in the young twig, 

 and the green hue Of which is transmitted through the 

 yet semi-transparent 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 



