200 
PLANT STUDIES 
ravages of animals (see 105). Examine Figs. 176, 177, 
178, 179, 180, 181. 
142. Anatomical adaptations. It is in connection with 
the xerophytes that some of the most striking anatomical 
adaptations have been 
developed. In such 
conditions the epider- 
mis is apt to be cov- 
ered by layers of 
cuticle,, which are de- 
veloped by the walls 
of the epidermal cells, 
and being constantly 
formed beneath the 
cuticle, may become 
very thick. This 
forms a very efficient 
protective covering, 
and has a tendency to 
diminish the loss of 
water (see 35). It is 
also to be observed 
that among xerophyfces 
there is a strong de- 
velopment of palisade 
tissue. The working 
cells of the leaves next 
to the exposed surface 
are elongated, and are 
directed endwise to 
the surface. In this way only the ends of the elongated 
cells are exposed, and as such cells stand very closely to- 
gether, there is no drying air between them. In some 
cases there may be more than one of these palisade rows 
(see 32). It has been observed that the chloroplasts in 
these palisade cells are able to assume various positions in 
b a, 
FIG. 177. Two plants of common gorse or furze 
(Ulex), showing the effect of environment : b 
is a plant grown in moist conditions ; a is a 
plant grown in dry conditions, the leaves and 
branches having been almost entirely developed 
as thorns. After LOTHELIER. 
