40 BRITISH PLANTS 
II. Internal Xerophytic Tendencies. 
1. Thickening of the Cuticle-——The cuticle is a layer or 
membrane formed by the external walls of the epidermal 
cells (Fig. 8). In xerophytes this becomes thickened and 
strongly cuticularized. The latter condition is brought 
about by the deposition in the walls of a waxy substance 
called cutin, a body closely allied to cork, which renders 
the membrane impermeable to water. 
Fic. 8.—SrectTion oF Part or A Prne-LEAF, WITH DEEPLY-SUNK 
Stoma (a). (HicHiuy Mae@niriep.) 
b, guard-cells ; c, stomatal pit; d, air-cavity ; e, cuticle ; /, epidermis; 
g, thick-walled hypodermis (sclerenchyma) ; h, chlorophyll-tissue. 
2. Diminution in the Volume of the Intercellular Air- 
Spaces.—The cells of the leaf are packed closely together, 
thereby impeding transpiration. 
3. The Stomata are reduced in Number and placed in 
sheltered positions in pits and grooves, the entrance to 
which is often closed by hairs—e.g., heaths (Fig. 9), 
marram-grass (Fig. 11). The stomata thus come to be 
in moist chambers. In most plants, however, each 
stoma is sunk in its own pit—e.g., pine (Fig. 8). 
