EPIDEESnS. 



27 



plants, there is an epidermal layer consisting of spiral cells (fig. 23), 

 containing air. 



The epidermis is usually formed by a layer or layers of compressed 

 cells, ■which assume a more or less flattened tabular shape, and have 

 their walls bounded by straight 

 or by flexuous lines. Fig. 72 e e, 

 represents an epidermis formed of 

 r^ular hexagonal cells; fig. 75, 

 one composed of irregular hexa- 

 gons ; whQe in fig. 74 the bound- 

 aries of the cells, «, are flexuous 

 and wavy. The cells of the epi- 

 dermis are so intimately united 

 together, as to leave no inter- 

 cellular spaces (fig. 77 e e). 



The epidermis is sometimes 

 thin and soft, at other times dense 

 and hard. In the former case it 

 may be easily detached from the 

 subjacent cells ; in the latter the 

 cells have become thickened by de- 



Fig. 7*. 



posits, and sometimes the layers are so produced as to leave uncovered 

 spots, which communicate with the interior of the ceU by canals passing 

 through the thickening layers, as in Cycas. In Eochea falcata (fig. 



Fig. 76. <• 



76) the epidermis, e e, consists of two layers of cells— the outer ones 

 large, the imier small. The epidermis of Agave and Hoya is thickened 

 by numerous secondary deposits ; such is also the case with that of 

 the branches of the mistleto. The cells of epidermis are usually 

 filled with colourless fluid, but they sometimes contain resmous and 



Fig 74. Epidennis, ftom lower surface of the leaf of Madder (RiMa tinctorum). e, CeU 

 of the Epidermis, s. Stoma. Pig. 75. Epidermal layer, from upper surface of a leaf of 

 Itanummlus cuprntUis when growing out of water, e e. Epidermal cells, sss s Stomate. 

 Fig 76 Vertical section of lower epidermis of the leaf of J!«!*«./oJoo«o. ««, Double epider- 

 m£ layer, with very large external cells. smaU internal ones, pierced by a stoma, s, which 

 commnniMteswithalacuna,!. p. Parenchyma of the leaf. 



