198 BOTANY 
xerophytic structure. It would appear that once the flax 
had its home on the dry heaths, where indeed it still 
flourishes in places; but that, being ousted from here by 
better-adapted competitors, such as the bracken fern and 
manuka, it took refuge in the swamp where some 
peculiar adaptability constitutional to the plant has 
enabled it to flourish ever since, 
Clumps of cabbage trees appear in the drier swamp 
regions, while, rising from the wetter parts, may be seen 
the niggerhead (Carex secta), which builds out of its 
dead roots and stem a kind of trunk, that lifts it above 
the surrounding water. Cotula coronopifolia, a native 
plant of the daisy family, as well as pennyroyal and 
several introduced buttereups, are abundant round the 
edges of swamps. 
XEROPHYTE SOCIETIES, 
The dry wind-swept heaths are the true home of the 
xerophyte. Plants forming the heath societies, as we saw 
in dealing with the leaf, have, as adaptations to a dry 
habitat, a variety of devices for conserving water. In 
carmichaelia and the tanekaha, flattened branches per- 
form the functions of leaves, and thus reduce transpira- 
tion, while, in the Wild Irishman, the work of leaves is 
done by rounded spines with the same result. Olearia 
furfuracea, a common heath plant of the daisy family, 
by means of a dense non-conducting layer of hairs on the 
under side of the leaf, and the tauhinu, by the rolling 
back of the two edges of the leaf-blade, have both solved 
the problem of water conservation. In the manuka, too, 
reduced leaf surface and thickened epidermis are 
drought-resisting characters. In New Zealand heaths the 
manuka is the predominant plant. Its extreme hardi- 
ness and ability to live under a great variety of con- 
ditions, even on the poorest soil, have enabled it to gain 
a footing almost everywhere, though it is to be noted 
that Hakea acicularis, an Australian hedge plant, has 
