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 
& 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 (Neriwm 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 
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