42 BRITISH PLANTS 
lignified walls, non-living, and containing only air. 
The cells are cemented together in sheets and columns, 
and form very effective screens between the living cells 
filled with water and the external air (Fig. 11). A 
covering of cork on stems and shoots serves a similar pur- 
pose. The presence of sclerenchyma in large and long-lived 
leaves gives them mechan- 
ical support, and keeps 
them from being easily 
torn and injured —e.g., 
New Zealand flax (Phorm- 
: ium tenax), Aspidistra. 
a 6. Some xerophytes con- 
Joie tain oil in their tissues, 
especially in the leaves. 
Where present, it un- 
doubtedly serves to check 
evaporation. Many strand 
and semi-desert plants are 
quite remarkable for their 
fragrance—e.g., rosemary, 
bay-laurel, sage, worm- 
wood, etc. 
ecco 
zs 
Cr 
IS 
Xerophytic Forms of Leaf 
and Shoot. 
The most important are : 
1. The Needle-Type, as 
: in the pine. The leaf is 
A, evergreen, thick and tough, 
Sf 
Fic. 10.—Salicornia herbacea (GLASS- 
WORT), SHOWING SUCCULENT STEMS 
AND Mrnute ADPRESSED LEAVES. 
(SuicgHtLy REepDucED. AFTER 
SowErey.) 
with a much reduced sur- 
face ; the internal cells are 
packed closely together, 
the cuticle is thick, and 
the stomata are reduced in 
number and sunk in pits. 
2. The Concrescent Type, as in many cypresses and 
junipers (Fig. 6). The leaves are thick and evergreen, 
very small, erect, and fused with the stem along nearly 
their whole length. There is very little internal air- 
space, the cuticle is thick, and the surface smooth and 
polished. 
