Vegetable Physiology for the IVar 1836. 57 



the later development of distinct cellular layers, which dis* 

 unite the single bark scales, or prepare for their disunion, or 

 even themselves form the scales. 



Upon the whole, we may suppose two main differences in 

 the later development of the cellular tissue of the bark; in 

 the first case the layers are developed outside the cellular 

 envelope, and in the other, the becoming thicker arises from 

 the development of a stratum of cells under the cellular layer; 

 in the first case it is generally cork substance which is formed 

 in the second bark {rhytidoma). 



There are besides a number of plants in which anew layer 

 of liber is annually formed, while the old layer dies away and 

 peels off, for instance Vitis xnnifera, Lonicera Caprifolium. 



The bark of dicotyledons consists therefore, as has been de- 

 monstrated in the cases specially examined by Mohl, of three 

 distinct layers, of very different structure, besides the epider- 

 mis. The exterior stratum of cells, which in many cases change 

 into a thick corky substance, is called by Mohl the cork layery 

 stratum suherosum sen phlceum. Link* calls this layer Epi- 

 jihloeum, outer rind {oberrinde); while he designates the inter- 

 mediate rind Mesophlceum and the inner rind Endophlceum, 

 The latter may evidently be compared with the layer of liber 

 of other botanists, and the intermediate rind with the green 

 cellular layer, the so-called cortical pith of many botanists. 



Mohlf has also published some very interesting observa- 

 tions on the occurrence of suberose tissue in the stems of 

 monocotyledons. Link and Dutrochet have also in their 

 late works before cited, admitted the occurrence of the su- 

 berose tissue in the rhizoma of Tamils Elephantipes. Ac- 

 cording to Mohl's microscopical observations it appears that 

 the brown layer of cork in Tamus Elephantipes perfectly 

 agrees in its structure with the cork of dicotyledonous trees. 

 The layer of cork on the basis of the stem consists only of a 

 few layers of tabular cells, which form regular rows perpen- 

 dicular to the surface of the stem. The exterior layers are 

 brown, and have died off; the inner layer situated near to the 

 rind is full of sap, colourless or yellowish. 



The thick layer of cork which surrounds the convex part 

 of the stem is composed in the same manner as the cork of 

 the cork-oak, of thin-sided cells which form regular rows per- 

 pendicular to the basis of the rind, etc. A distinction between 

 the rind and the cork can only be made in so far that the rind 

 is living, whereas the cork on the contrary is dry and dead ; 



• PhU. BoL, p. 282. 



I Observations on the Rhizoma of Tamus Elephantipes L. — T'u' 

 bingeuy 183G. 



Phil Mag,, S.3. Vol. 12. No. 71. Jan. 1838. I 



