The Struggle For Existence 203

flourishes best in water poor in lime. Others, again,
allege that sphagnum can grow only where there is
but a slight amount of nutritive matter dissolved in
the water. As time goes on, the mass of sphagnum dies
below, but the young shoots continue to live above.
As this goes on generation after generation, the mass
is raised and spreads, often encroaching on and
destroying surrounding vegetation. In some bogs,
sundews and bladderworts abound. Both are able to
exist where available nitrogen is scarce, for both trap
insects and small animals whose proteins they digest.
In the bladderwort, some of the leaves form small
bladders with a kind of lid, which by opening only
inwards, serves as a trap for small aquatic animals,
which enter and are there digested and absorbed. One
of the umbrella ferns and a creeping lycopodium (club-
moss) are also plentiful in certin bogs.

Salt-meadows are in much the same position as
bogs, for here, too, though water is plentiful, there is
present an excess of certain mineral salts, which would
prove fatal to plants too freely absorbing them. The
plants of the salt-meadows are therefore xerophytic in
structure. Reduced absorption must be balanced by
reduced transpiration. The most remarkable feature
of these plant societies of the coast is the succulent
water-storage tissue of which their members are
composed. This we see in the ice-plant of the cliffs, as
well as in the many salt-loving plants belonging to the
beet family e.g. salicornis and suaeda.

The mangrove, which is found plentifully in the
wide estuaries of the Auckland peninsula, is one of
the most remarkable of the sea-coast plants. The
peculiarities of the germination of this seed, and the
establishment of its seedling, as well as its development
of aerial breathing-roots, have already received atten-
tion. The mangrove is a plant which has, with