EPIDERMIS 49 



stomata, to be described later, no openings occur be- 

 tween the cells, even at their angles. 



67. The most characteristic feature of well developed 

 epidermis cells is the thickening of the external wall 

 and the deposition in the outer layers of this wall of a 

 waxy or fatty substance called cutin. This water-proofs 

 the walls to a large extent and prevents loss of water 

 through them by evaporation. The cutin is not de- 

 posited equally throughout the outer wall, but is least 

 toward the cell cavity and greatest at the outside. The 

 outer, strongly cutinized portion of the wall is often 

 very distinct in appearance from the remainder of the 

 wall and can sometimes be stripped off as a continuous 

 sheet, the cuticle. Often this is coated externally with 

 a waxy or resinous coating, the "bloom" of some 

 leaves or fruits. 



68. The cutinized layer extends, in many cases, not 

 merely over the outer surface of the cell wall but even 

 down between the adjacent cells for some distance. 

 In roots, on the other hand, the younger parts are not at 

 all cutinized and further from the tip the cutinization is 

 only comparatively slight. The root hairs are cutinized, 

 if at all, only in their basal portion. 



69. While the epidermis always consists at first of 

 but one layer of cells it becomes two to four layered in 

 some plants, e.g. oleander (Nerium oleander), rubber 

 plant {Ficus elastica), various cactuses (Opuntia), etc., 

 by subsequent periclinal division (i.e. division by the 

 formation of a cell wall parallel to the outer surface) 

 of the original layer. The outer walls of these new 

 layers may become cutinized successively, from the 

 outer toward the inner layers. 



70. The hairs originate mostly as outgrowths of single 

 epidermal cells. In the case of young roots the epidermal 



