32 NEW ZEALAND PLANTS. 
enables the plant to make considerable patches on the gravelly shore, 
where it grows far more luxuriantly than on the peaty ground which 
it also inhabits. On the stony shore of Foveaux Strait a small plant 
of the cress family, the shore-cress (Lepidiwm tenwcaule), puts down 
an exceedingly long root in quest of the fresh water which flows sea- 
ward beneath the stones. In the same locality a forget-me-not with 
small white flowers (Myosotis pygmaea var. Traillic) is also common. 
On the shores of Cook Strait two rather unexpected mountain- 
plants, the spear-grass (Aciphylla squarrosa) and the striking silvery 
mats of a variety of Raoulia australis, are common. In similar 
stations two usually erect shrubs, the shrubby ribbonwood (Plagi- 
anthus divaricatus) and the common coprosma (Coprosma propinqua), 
form veritable mats. This happening certainly is not due to wind 
alone, as erect plants in the same neighbourhood testify, but the 
heat from the stones and the bright light may be controlling - 
factors. 
On many parts of the coast, sand is continually bemg brought 
on to the shore by the advancing waves. In the neighbourhood of 
high-water mark the shore soon becomes dry, and the sand is then 
borne landwards by any wind coming from the sea. Where the 
sand accumulates faster than it is blown away, a hill, or dune as it 
is frequently called, is formed. Any obstacle in the path of the 
blown sand will also arrest its progress and cause its heaping-up. 
The dunes of New Zealand are of great extent, and occupy an area 
of more than three hundred thousand acres. In some parts of the 
coast the belt of dunes is more than six miles in width, and in the 
north of the Auckland Provincial District, on the west of Stewart 
Island, and elsewhere, the sandhills attain a height of several 
hundred feet, though usually they are much lower. 
Frequently the dunes are very unstable, and in some places so 
much so that great areas of moving sand exist. These “‘ wandering 
dunes,” as they are called (fig. 18), imsidiously advancing inland, 
do great damage — burying fertile fields, filling up valuable flax- 
swamps, choking watercourses, and overwhelming forests, planta- 
tions, pasture-lands, and even human dwellings. Happily nature 
has done much to stop such inroads, and the wandering dunes of 
New Zealand are chiefly the result of damage done by grazing- 
animals breaking the surface of the sand, and by fire removing the 
natural safeguard, its plant-covering. 
