Jay. 1911.] BOTANICAL SOCIETY OF EDINBURGH 123 
at the same time the wind-borne silt and sand is caught 
and held, so that, by degrees, the stony substratum be- 
comes the sub-soil. On the other hand, the upper layer, 
formed altogether through the action, direct and indirect, 
of the vegetation, will consist of silty loam mixed with 
humus, averaging perhaps 5 cm. in depth, or even more, 
becoming capable of supporting a closed plant-covering of 
a steppe character. 
8. Steppe. 
The absence of bare spaces between the plants, the 
dominance of the tussock-form and the presence of many 
of the species of the Raoulia association, together with a 
number of others, defines the steppe association. 
The association is not altogether virgin, since sheep, 
hares, and red-deer graze upon the herbs and shrubs, but 
this has affected luxuriance of growth rather than brought 
about any fundamental change.! 
Poa Colensoi is, in many places, the chief tussock grass, 
the individual plants sometimes growing closely together 
and excluding other vegetation. Where the upper soil is 
deeper, the much more robust Poa cespitosa is plentiful, 
and the character of the association is then that of ordinary 
tussock-steppe. Poa anceps var. is also a common grass 
in some parts; it does not form erect tussock, but the 
culms and leaves are more or less prostrate, and form a 
thick mat which may contain much dead matter and is 
then a soil-maker. But this grass plays a more important 
part on the firmer débris-fields (“shingle-slip”) of the 
adjacent slopes. Between the tussocks, and benefiting 
from the shelter these give, there are patches of Styphelia 
Fraseri, small mats of Coprosma brunnea, dwarfed Car- 
michaelia grandiflora (usually much eaten by hares and 
sheep), Hydrocotyle nove-zelandie growing close to the 
ground, Luzula campestris var. (Juncac.), Craspedia wni- 
flora var., Lycopodium fastigiatum, Ranunculus foliosus, 
Asperula perpusilla (Rubiac.), considerable round patches 
of Coriaria thymifolia and the feathery C. angustissima 
(Coriariac.), abundance of Pimelea levigata var., repens 
1 The presence of grazing animals, by reducing the amount of shelter, 
is favourable to steppe and antagonistic to forest. 
