CUSHION PLANTS 193 
plant growth is characteristic of semi-desert regions, 
where the points of similarity of environment to those 
of the mountain-tops are evident. This cushion form 
has many advantages for the alpine plant. It keeps it 
warm in winter and cool and damp in summer; it 
allows it to produce a great amount of blossom 
without the necessity for extensive growth; it resists 
the utmost efforts of furious gusts of wind almost as 
well as would a half-buried stone; on the most storm- 
swept cliffs its fresh green blobs “welcome every 
changing hour, and weather every sky.” Fig. 32 
shows a boss of this kind, composed of the Cushion 
Pink (Silene acaulis), with an admixture of Filmy Fern 
(Hymenophyllum unilaterale) and a Moss (Mnium 
hornum). The shrubs of the alpine zone are mostly 
small and creeping, weaving themselves among the 
vegetation, and with low grasses and sedges forming 
a mat which is equally resistant to all inimical condi- 
tions. Their leaves are small, to avoid damage by 
wind or by excessive transpiration. In some genera— 
for instance, Veronica—the diminution of leaf surface 
accompanying more elevated habitat is very striking. 
In the New Zealand lowlands broad-leaved forms 
(Fig. 34, left) are met with, which give way, as one 
ascends to 8,000 feet, to such forms as V. Hecton 
(Fig. 34, right), in which the leaves are reduced to 
mere scales, and the plant much resembles some of the 
Cypresses or other Conifers with marked xerophile 
characters. 
Other plants, again, escape climatic rigours by 
burrowing underground and throwing up short aerial 
stems in summer; the spindly plants of the lowland, 
with diffuse stems, and also the light-rooted annuals, 
13 
