STRUCTURE.] BARK CORK. 193 



being an outer pith, the pith an interior bark, the liber 

 being the wood of the bark, and the wood the liber of the 

 pith. 



In an anatomical point of view, the observations of Mohl 

 are the best and most complete which have hitherto been made 

 upon this very important subject : they, and many more of 

 considerable value, by Dutrochet, Link, and others, have given 

 rise to a peculiar nomenclature for the parts of the bark, in 

 order to avoid the somewhat indefinite ideas which attach to 

 the older terms. 



Bark may be described anatomically as composed of four 

 separate parts : 1. The Epidermis, which is continuous with 

 that of the leaves, resembling what is found upon their veins, 

 like it composed of cells a little lengthened, and rarely fur- 

 nished with stomates; it often bears hairs. 2. The Epiphloeum 

 of Link, Phlceum or Peridermis of Mohl, consisting of several 

 layers of thin- sided tabular cells, rarely coloured green. In this 

 part Achille Richard distinguishes an inner colourless layer 

 which he calls the Mesoderm. 3. The Mesophloeum of Link, 

 or herbaceous or cellular integument of others, composed of cells 

 usually green, and placed in a different direction from those 

 of the epiphloeum ; sometimes, as in the Cork tree (Quercus 

 Suber), containing cellular concretions. 4. The Endophloeum 

 or Liber, of which a part is cellular and a part composed of 

 woody tubes. The cellular face of the liber, which serves to 

 connect it with the medullary plates, A. Richard distin- 

 guishes by the name of Subliberian layer, or Endoderm. These 

 are modified differently in different trees ; and the appear- 

 ances of Cork in many plants, of thin white lamellae or hard 

 plates in others, are so produced. Usually each stratum has 

 a separate growth, which takes place by the addition of new 

 matter to its interior; thus the endophloeum, or liber, grows 

 next the alburnum, the mesophloeum next the endophloeum, 

 and the epiphloeum next the mesophloeum; the epidermis 

 does not grow at all. Such growth is often indicated by con- 

 centric circles, which correspond in each layer with the zones 

 of wood. 



When the substance called Cork is formed, the epiphloeum 

 consists of polyhedral cells, which multiply with unusual 



VOL. i. o 



