CELLULAR INTEGUMENT. 59 



forated with holes or pores, forming the medium of 

 communication between the different cells, and border- 

 ed with a sort of small and glandular ring. The whole 

 of the tissue was extremely delicate, but particularly 

 in the several parts of the flower, where the slightest 

 touch stained it, and the slightest pressure destroyed it. 

 It was also speedily destroyed by maceration in water. 

 If the cells happened to be empty it was transparent 

 and colourless, but if filled with juice it was generally 

 green, though sometimes brown, yellow, or red, com- 

 municating its acquired colour to the epidermis, wheth- 

 er in the leaves, petals, or other parts of the plant."* 



The mere empty cells form the cellular membrane, 

 and the same cells when filled with their appropriate 

 and frequently coloured juices, constitute the Paren- 

 chyma or pulp, which forms the great mass of succulent 

 plants and pulpy fruits. No plants are destitute of 

 this integument, for it is the seat of operations in- 

 dispensably necessary to healthy vegetation ; but 

 these operations will be more fully explained in our 

 chapter on the uses of leaves. 



SECTION 3. 



CORTICAL LAYERS. 



If a stem of the Currant or a branch of the Lime 

 tree be divided transversely, we find within the cellu- 

 lar integument a series of concentric or Cortical Layers, 

 corresponding in number to the age of the stem or 

 branch we examine. In some instances they constitute 



* Keith. 



