THE STRUGGLE FOR EXISTENCE 203 
flourishes best in water poor in lime. Others, again, 
allege that sphagnum ean 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 smail 
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 certain 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., salicornia and sueda. 
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 its 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 
