Dune. 75 
Spinifex hırsutus, one or both according to the botanical district. In the Northern 
and Central botanical provinces, where both plants are present, they rarely 
intermix, while their characteristic colours, — silvery (Spinifex), yellow (Seirpus), 
plainly indicate which dominates, giving the dune also a special physiognomy. 
5. hırsutus does not extend inland for any distance, but S. frondosus occurs, 
 wherever there is drifting sand. In the S. of the South Otago district Fes- 
Zuca Littoralis is an early comer, and it is sometimes a primary dune-builder. 
Occasionally, the tufts of Spinzfer or Scerpus form a close covering, but usually 
there are more bare patches than vegetation. At certain places on the W. 
coast of the Ruahine-Cook district a very uniform foredune, looking like an 
artificial embankment, extends for several kilometres at a time covered with 
Spinifex. 
Embryonic dunes frequently occur both on the foreshore and sand-plain. 
A plant of either of the sand-binders becomes established, functions as an 
obstacle, a tongue of sand is formed on its leeside into which the rapidly- 
growing rhizome extends, and with simultaneous increase of sand and growth 
of plant a small dune is formed. 
As sand-grass dune becomes more stable, Calystegia soldanella, Calam- 
agrostis Billardiert, Festuca httoralis and Scirpus nodosus will gain a footing 
and probably also some of the sand-tolerating shrubs. The rarer Zuphorbia 
glauca belongs to the same association. In Stewart Island, Sonchus Zittoralis 
may be present. Calystegia soldanella often covers the sand completely with 
a shining green mantle. Low dunes of that kind persist for a considerable 
time, the dune itself acting as a solid obstacle thus causing a protecting wind- 
trough to be formed between itself and the advancing sand. 
ec. Shrub-dune (Plate V Fig. 7). 
Semi-stable shrub-dune is the second stage of progressive dune-evolution. 
The shrubs present are only those adapted to drifting sand, e.g., Coprosma 
acerosa, one or more of the species of Cassinia, and Pimelea arenarıa. Gene- 
rally, C. acerosa or Cassinia is dominant, the former conspicuous through its 
curious growth-form and reddish colour, whereas the Cassinia is grey or 
yellow, according to the species. aha soldanella, Fesituca httoralis, Calam- 
agrostis Billardieri, Scirpus nodosus and sometimes Arundo insg may be 
members of this association. 
At a greater distance from the sea, or when exposed to weaker 
sand advance or erosive wind-action, the above shrubs will form a closed 
covering and may be reinforced by others, especially Leptospermum scopar- 
zum. The great tussocks of Arundo conspicua, and the /ris-like green 
masses of Phormium tenax, are frequently present, the latter being extre- 
mely common in’ the North Auckland district. There Se ERDRSPEr Re 
ericoides and ae en nö erect bu ggg | mats, are 
very a abundant. 
