44 BRITISH PLANTS 
of acacia, Fig. 13), or by shoots which function as leaves. 
These shoots are of two kinds : 
(a) The leaves are small and green or reduced to scales, 
and all the stems take over the functions performed by 
Fic. 13.—Spppiina or Acacia melano- 
xylon, SHOWING TRANSITION FROM 
ORDINARY PETIOLE (b) TO PHYLLODE (d). 
(Asour Hatr Natura Size.) 
In c the petiole is slightly winged. 
a, cotyledons ; e, root-nodules. 
leaves, as in switeh- 
plants—e.g., horsetail, 
broom (Fig. 14). 
(b) The leaves are 
again reduced to scales, 
but most of the 
branches are flattened, 
and resemble ordinary 
foliage - leaves — e.g., 
butcher’s - broom 
(Fig. 15). These flat 
branches, known as 
eladodes or phyllo- 
clades, are at once 
distinguished from true 
leaves by their position 
in the axils of the 
scales, and _ because 
they themselves often 
bear scales, and even 
flowers, on their upper 
surface or along their 
edges. Cladodes are 
distinguished from 
phyllodes in the same 
way, for, after all, the 
latter are only parts of 
leaves, while cladodes 
are shoots. 
7. Lack of nutrition 
sometimes reduces 
shoots to thorns, and 
leaves partially or en- 
tirely tospines, Thorny 
plants are pronounced xerophytes, and form a con- 
siderable part of the bush and scrub vegetation of semi- 
deserts. In England, gorse is characteristic of dry 
heaths. Some plants even have two forms ; Ononis arvensis 
(rest-harrow) growing on the seashore usually develops 
