LATERAL AND INNER EPIDERMAL WALLS 



113 



this lateral interlocking of the epidermal cells in a very characteristic 

 manner (Fig. 26 b). In most Dicotyledonous leaves the folding of the 

 lateral walls is restricted to the lower epidermis, which usually possesses 

 a relatively thin outer wall. Where the waviness affects the whole 

 extent of the lateral wall, it adds to the rigidity of the entire cell, and 

 so helps to prevent collapse when water is withdrawn. In delicate 

 perianth-leaves the folds are often supplemented by radial flanges for 



z 



z 



Fig. 20. 



A, B. Epidermal cells with folded lateral walls. A. From the abaxial foliar epidermis 

 of Impatient parviflora. X420. B. From the abaxial foliar epidermis of Fcstuca ovina ; 

 z, a semi-lunar dwarf -cell. x400. C. Subepidermal mechanical cells from a pale of 

 Oriiza saliva, with tooth-shaped protuberances (after Von HOhnel) ; a, cell with one, 

 b, cell with two sets of teeth. 



similar reasons ; these flanges may even become hollowed out and thus 

 transformed into tubular buttresses, which support the tangential walls 

 and thus increase the rigidity of the whole epidermis. 



The inner epidermal walls are responsible for the firm attachment 

 of the epidermis to the underlying tissues, a duty which they are 

 generally able to perform without the aid of any special contrivances. 

 The average epidermis, indeed, adheres so firmly to the mesophyll that 

 one cannot easily strip it off without tearing away one or more sub- 

 epidermal layers as well. A unique and exceedingly effective mode of 

 attachment of the epidermis to the hypodermal layer is described by 

 Von Hohnel 58 as occurring in the pales of certain Grasses (Oryza sativa, 

 Sorghum vulgare, Setaria gcrmanica, Triticum Spelta, Hordeutn vulgare); 

 the fibrous cells situated beneath the outer epidermis of the pale 

 present a serrated appearance owing to the presence of numerous 

 lateral protuberances of their walls, which fit into corresponding 



ji 



