ELEMENTARY STRUCTDKE. 



39 



Fig. 76. 



Fig. 77. 



Fig. 78. 





■ ' ( V ) I ^ "■' 



/ V. 



Kgr. 76. Epidermal tissue from the leaf of the Iris (^Iris germam'ca). p, p. 



Cuticle, s, s. Stomata. e, e. Epidermal cells. After Jussieu Fig. 



77. Epidermis of the Maize, a. a. Stomata. 6. b- Zigzag reticulations 



formed by the sides of the cells Fig. 78. Sinuous epidermis -nith 



stomata, from the garden Balsam. 



(Jig. 76); in that of the Maize they are zigzag (Jig. 77); whilst 

 in the Madder, the common Poh^podv, &c., they are very ir- 

 regular or sinuous (fig. 78); and in the epidermis of other 

 plants we find them square, rhomboid, &c. 



Ordinarily in European plants and others the epidermis is formed 

 of hut one row of cells (Jigs. 79 and 83), but in tropical plants 

 we frequently find two (Jig. 80), three, or more, as in the Oleander 

 (Jig. 81), by which provision that plant is admirably adapted, as 

 will be afterwards explained, for growth in a hot dry climate. 

 The upper walls of the epidermal cells are generally much 

 thickened by layers of secondary deposits, which gradually be- 



Fig. 79. Vertical section of the leaf of the Maize, showing the epidermis, a, 

 formed of one row of cells, with projecting hairs, g,g- 



come thinner, and terminate on the side walls (Jig. 82). This 

 thickening of the upper walls of the epidermal cells may be 

 especially obser^-ed in leaves of a leathery or hardened tex- 

 ture, as in those of the Oleander (fg. 81), Aloes, Hoya (Jig. 

 82), Box, Holly, &c., and in the stems of Cactaceae (fg. 

 83). These thickening layers upon the inner walls of the 

 upper or external surface of the epidermal cells were formerly 

 confounded with the Cuticle or thin pelUcle which is situated 

 on the outside of the epidermis (Jig. 82, a). Mohl, to whom 

 D 4 



