SAND-BINDING PLANTS. 33 
In order that a plant can live on drifting sand it must have the 
power of binding that unstable compound into a firm mass. Plants 
with rapidly growing underground stems, which have the power of 
rooting near the tips of the branches and putting forth new shoots 
as fast as the old ones are buried, are sand-binding plants par 
excellence. With few exceptions, wherever sandhills exist on the 
globe, such plants accompany them. 
In New Zealand there is a most excellent example in the pingao 
(Sewrpus frondosus). Its thick, rope-like stems, commonly called 
roots, form a perfect entanglement inside the dune, and its semi- 
tussocks of stiff, golden-coloured leaves crown many sandhills from 
the North Cape to Stewart Island and the Chathams. Unfortu- 
nately, rabbits and some other animals do not despise this plant, 
notwithstanding its most unappetizing-looking leaves. In conse- 
quence they destroy this natural protector of our shores, which 
came into being in a land where grazing-animals, the moa excepted, 
were unknown. It is of great interest biologically that sandhill 
conditions have called forth a sand-binding endemic plant of the 
same growth-form as that of sand-binders the world over. Also, 
the pingao must be a plant of long descent, since it has no near 
relative in any part of the earth, belonging, as it does, to an 
endemic subgenus of Scirpus, Desmoschoenus by name. 
The silvery sand-grass (Spinifex hirsutus), which grows wild in 
Australia as well as in New Zealand, is another very important sand- 
binder. Its stout stems, often many feet in length, at first creep 
over the surface of the sand, firmly fixing themselves by means of 
many roots. Finally they are buried, and the tufts of long flexible 
leaves, covered densely with soft silvery hairs, project out of the 
sand. The pollen-bearing and ovule-bearing plants are distinct. 
When the seeds are ripe, the mature inflorescence breaks off, and, 
borne by the wind, hops on its long spines over the sandy shore lke 
some huge insect, until, at last falling to pieces, the “seeds” are 
deposited and finally buried. 8S. hirsutus naturally builds up fairly 
stable dunes, which in some places have a surface so even as to 
look like a railway-embankment (fig. 19), as in the case of the dune 
fronting the shore near Waikanae, in the Wellington Provincial 
District. Spinifex, being less tolerant of frost than the pingao, 
reaches only the northern parts of the South Island, but it is 
present on all dunes of the North Island. 
3—Plants. 
