ORGANS OF NUTRITION OR VEGETATION. 



23 



-Jt 



GENERAL INTEGUMENT. 



45. General integnment is the name given to the external cellular 

 covering of plants. It can be 



easily detached from young 

 leaves and stems, usually in 

 the form of a colourless trans- 

 parent membrane. By pro- 

 longed maceration it has been 

 shown to consist frequently of 

 two layers ; a superficial, called 

 Cuticle or Pellicle (fig. 69 p p), 

 and a deep layer, usually called s - 

 the Epidermis (fig. 69 e e). 



46. The Superficial Pellicle 



(pdlis, skin) is a very thin con- 

 tinuous membrane, which is 

 spread over all parts except the 

 openings of the 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, considering it as a secretion on the outside 

 of the cells, while Mohl and Henfrey look upon it as composed of the 

 altered primary walls of the cells. In fig. 70, it A h 

 is represented as detached from the leaf of the ; '^/i 

 cabbage, forming a sheath over the hairs, hhhh, and IL 



leaving slits, s s, corresponding to the openings of 

 the stomata. This pellicle appears to be similar to /A\ / 'V 

 the intercellular substance surrounding cells, and \ vA 

 to the definite mucus which is conspicuous in some I 1{=1 

 sea- weeds (fig. 29 V). It is possible that this / I'll /j 

 matter, in place of being produced on the outside ( /" ? 

 of cells, may be formed within them, and ulti- 

 mately deposited externally by passing through 

 their parietes. On the inner surface of the pel- 

 licle the impressions of the epidermal cells are 

 sometimes observed (fig. 69 p). The pellicle is h 



the only layer of integument which is present in 70 



aquatic plants, and in some of the lower tribes. 



47. The Epidermis (tvl, upon, and li^et, skin), (fig. 69 e e,) is 



C 



Fig. 69. General integument of a leaf of Iris germanica. pp. The Cuticular pellicle with slits, 

 /, lying upon the proper epidermis, e e, formed of hexagonal cells, and furnished with stomata, ts. 



Fig. 70. Pellicle of Cabbage detached by maceration, covering the hairs, hhhh, and having 

 openings, ss, corresponding to the stomata. 



