22 CUTICLE AND EPIDERMIS. 



surface from the deepest root to the highest leaf, called the 

 cuticle. Within this covering we rind another distinct zone, 

 called the bark ; within the bark we rind the main axis of the 

 plant, called the wood, which is composed of two portions, one 

 ascending-, and called the stem, the other descending, and termed 

 the roof. "Within the stem we find a soft, spongy substance, 

 denominated the pith. To the root and stem are attached 

 branches, and to those of the stem are attached leaves, flowers, 

 and fruit. 



We shall describe the above organs in the order laid down. 



Section 1. — Cuticle and Epidermis. 



35. The cuticle is a thin continuous membrane, covering the 

 whole plant, even the minutest hairs, with the exception of the 

 stomata, which it sometimes enters and lines the cavity beneath. 

 It is thought by some to be a secretion of the subjacent cells, by 

 others that it is a cell membrane, and by others still, that it is 

 organic mucus. It is easily observed in the Cabbage. It is the 

 only covering of some aquatic plants. 



36. The epidermis is composed of flattened cells, adhering 

 to each other by their edges, and forming a continuous covering 

 over the whole plant, except the stigmatic surface, spongioles, 

 and parts growing under water, and is generally composed of 

 a single layer of cells, but sometimes in succulent plants of two 

 or more layers. The epidermis of the Oleander is composed of 

 three or four layers of thick-sided cells. The joining lines of 

 the cells may be seen on the leaves of plants by the microscope, 

 presenting, generally, hexagonal figures more F . a 



or less regular. Sometimes, however, the 

 lines produce irregular figures, assignable to 

 no geometrical form. The epidermis may 

 be easily separated from the subjacent layer 

 of the leaves of the Iris or Lily, by means of 

 a sharp knife, and examined in water with 

 the microscope. If the microscope be good, 

 the cellular cavities will be easily seen, oth- 

 erwise the flattened surface only can be dis- 

 tinguished. 



37. On the lines which separate the cells that compose the 

 cuticle, small oval spaces are observed, which are called stomata, 



35. What is the outicle '■ In what plants easily observed ! Of what 

 plants is it the only covering ! — 86. Of what is the epidermis composed? 

 IIow may the epidermis bo obtained and examined ? — 37. What are stomata ? 



