SPHAGNUM-CUSHIONS AND PEAT. 13.53 
rapidly drawn into the stems and leaves through capillarity and held 
firmly as in a sponge, the capillary spaces between the drooping 
branches also functioning in this regard. 
The surface of a sphagnum-cushion becomes so dry during a period 
of drought that it is readily set on fire. This fact is strong evidence 
that a continuous stream of water is not being conducted upwards, by 
capillarity, from the wet moss or water below. Indeed, a sphagnum- 
cushion is dependent for its water-supply on the rainfall, and can 
exist only where this is abundant, an excessive precipitation allowing 
the plant to occupy even a rock-surface. As the upper portion of a 
sphagnum-cushion grows, its lower part dies and is converted into peat, 
great masses of which frequently accumulate. Such peat is used for 
fuel in many parts of the world, and at Waipahi, in Southland, is cut 
to some extent for that purpose. New Zealand peat in general is 
formed by many other plants in addition to sphagnum, or this latter 
may be altogether wanting. The upper surface of a sphagnum bog 
continues to rise in height through the rapid elongation of the apices 
of the moss-stem, and any plants growing thereon must, like dune 
vegetation, be able to grow upwards faster than they are buried. 
The small pine Dacrydium Bidwillii, common on subalpine bogs, is 
frequently buried by the too rapid upward growth of the moss, and 
may be observed in all stages of burial. On the sphagnum-cushions 
themselves grow many plants which cannot live under the adverse 
conditions provided by peat itself, for here they have at their 
disposal purer water than that of the peat. 
Coming next to bogs, it must be first explained that these differ 
from swamp in that, though the soil is saturated with water at all 
times of the year, and shallow pools may be present, the whole 
surface of the ground is not covered with water. Further, swamp- 
water contains more or less lime, but this, of course, is absent in 
the acid bog-water. The soil consists of peat, which is sometimes 
many feet in depth. The bog-water is coffee-coloured, and contains 
much organic matter. Those small plants termed ‘ bacteria,’’? some 
of which play such an important role in adding the all-important 
nitrogen-compounds to soil in general, are few or wanting in bogs. 
Bogs originate in various ways, as, for example, from swamp ; 
through formation of peat under the influence of a wet climate, and 
on which Sphagnum gains a footing ; from water lying in wet hollows ; 
from mountain-streams frequently flooding the adjacent ground ; 
