122 TRANSACTIONS OF THE [ Sess. Lxxv. 
favours their rapid germination, upon which the root easily 
reaches the water-supply at a few millimetres beneath the 
surface of the cushion. 
It is easy to see that as the epiphytes on the cushion 
increase in size they cut off the light-supply from its leaves, 
which are none too many on each stem at best, and the 
Raoulia dies piece by piece, leaving behind it a deep layer 
of humus. Since there are large Raoulia cushions dotted 
everywhere at a distance apart of 30 cm. or so, while fresh 
cushions are continually becoming established on the 
intermediate stony ground, it is evident that what was 
originally an edaphic desert may be rapidly converted 
into fairly fertile ground by the agency of Raoulia 
Haastii alone, aided by the abundant supply of mois- 
ture. The xerophytic moss Racromitriwm lanugunosum 
also plays some part as a humus-former, as do likewise 
the other species present of Raoulia, especially the 
quite low but dense silt-holding cushions or patches of 
R. lutescens. 
In addition to the species already noted, certain others 
early on occupy the stony ground between the cushions, 
though these latter still remain dominant. Amongst these 
early comers are: Veronica Bidwillii (Scrophular.), which 
forms on the stones open green mats of slender, wiry, 
creeping stems and short leafy branches; Styphelia Fraseri, 
in broad brownish patches, the short erect wood stems 
raised 3 cm. above the stones; Coprosma brunnea (Rubiac.), 
with stiff prostrate woody stems; Muchlenbeckia axillaris 
(Polygonac.), forming round patches, its slender, almost 
black wiry branches flattened to the ground and the small 
yellowish-green leaves almost touching but held nearly 
vertically; Wahlenbergia saxicola, with its small open 
rosettes and, in their season, rather large white flowers; 
Geranium sessiliflorum, in small circular patches made up 
of several rosettes flattened close to the stones and small 
tussocks of Poa Colensoi (Gramin.). As the last-named 
increase in numbers, the tallness and density of this 
growth-form giving it an advantage over the creeping 
plants, etc., the species, by degrees, becomes very common. 
Also it adds further humus to the soil by its decay, and 
