26 SUPERFICIAL CUTICLE OE PELLICLE. 



skin) is a very thin continuous membrane, 'whicli is spread over all 

 parts except the openings called stomata ; in some cases entering these 

 openings, and lining the cavities beneath them. 

 It is formed from the epidermal cells below it. 

 Treviranus, Schleiden, and Payen, consider 

 it as a secretion on the outside of the cells, 

 ' while Mohl and Henfrey look upon it as com- 

 posed of the altered primary walls of the cells. 

 J Mitscherlich regards it as a corky substance, 

 which preserves the humidity of the plant by 

 '' preventing the evaporation of moisture. This 

 substance is considered by him to be an im- 

 portant constituent of the cell-wall. In many 

 plants we meet with a corky epidermis com- 

 posed of ceUs containing air. The cork cells 

 are flat and thin- walled; and in some cases 

 Fig. rs. *^^y ^^^ ^^ peeled off, as ui the cork oak. In 



fig. 73 the peUicle is represented as detached 

 from the leaf of the cabbage, forming a sheath over the hairs, hhhh, 

 and leaving slits, s s, corresponding to the openings of the stomata. 

 The pellicle is perhaps similar to the intercellular substance sur- 

 rounding cells, and to the definite mucus (collenchyma) which is seen 

 in seaweeds (fig. 29 h). It is possible that this matter, in place of 

 being produced on the outside of cells, may be formed within them, 

 and ultimately deposited externally by passing through thek parietes. 

 On the inner surface of the pellicle the impressions of the epidermal 

 cells are sometimes observed. The pellicle is the only layer of in- 

 tegument which is present in aquatic plants, and in some of the lower 

 tribes. 



The Epidermis (!«', upon, and di^/ia, skin), (fig. 72 e e), is ex- 

 tended over all the parts of plants exposed to the air, except the 

 stigma. The internal cavities of seed-bearing organs are lined by a 

 delicate membrane, termed Epithelium (It/, upon, 6dXXiiv, to flourish). 

 On the extremities of newly-formed roots the integument consists of 

 loose cells, which are either the ordinary cellular tissue of the plant, 

 or an imperfectly-formed epidermis, which has received the name 

 of Epiblema (M, upon, and ^Xrj/ia,, wound, as being the tissue which 

 first covers wounds). This latter kind of tissue occupies the place of 

 the epidermis, in the parts of plants which are always under water. 

 The cells forming the sheath of young roots are often densely filled 

 with granular protoplasm, and contain nuclei. They become coloured 

 in Beale's carmine solution. On the aerial roots of Orchidaceous 



Fig. 73. Pellicle of Cal)bage, detached by maceration, covering the hairs, Tihhh, and 

 having openings, s s, corresponding to the stomata. 



