138 



THE EPIDERMAL SYSTEM. 



B85, Cells and stomata of the epidermis of Oxalis violacea ; and 535, of Convallaria racemose. 



680. Cuticle. The surface of the epidermis at length becomes itself coated with 

 a delicate, transparent pellicle, not cellular, called the cuticle. It varies in consis- 

 tency, being thicker and stronger in evergreen and succulent plants. It seems to 

 be merely the outer cell wall of the epidermis thickened and separated from the 

 newly-formed wall beneath it. 



681. The hairs which clothe the epidermis are mere expansions of 

 its tissue. They may each consist of a single elongated cell, or of a 

 row of cells. They may also be simple, or branched, or stellate, or 

 otherwise diversified. 



682. Glands are cellular structures serving to elaborate and contain 

 the peculiar secretions of the plant, such as aromatic oils, resins, honey, 

 poisons, etc. A gland may be merely an expanded cell at the summit 

 of a hair, or at its base, and hence called a glandular hair (Labiatae). 

 Or it may be a peculiar cell under the epidermis, giving to the organ a 

 punctate appearance, as in the leaf of lemon. Other glands are com- 

 pound and either external (sundew), or internal reservoirs of secretion 

 (rind of orange). 



683. Stings are stiff-pointed, 1-celled hairs expanded at base into a 

 gland containing poisonous secretion. An clastic ring of epidermal cells 

 presses upon the gland so as to inject the poison into the wound mado 

 by its broken point (nettle). 



684. Prickles are hardened hairs connected with the epidermis 

 alone, thus differing from spines, which have a deeper origin. Exam- 

 ples in the roae. 



