120 NEW ZEALAND PLANTS. 
surface of the ground. Where the soil is wettest, prolongations from 
the root pass upwards above the water and probably function in the 
same manner as the breathing-roots of the mangrove (fig. 80). 
Between lakes, swamps, bogs, grassland, and rain-forest there is 
a rather close connection. Sedges, raupo (Typha angustifolia), rushes, 
and rush-like plants growing in the shallow water near the margin of 
a small lake may in time, through their decay, turn by slow degrees 
that part into dry ground, and advance farther and farther into the 
lake until a water-surface is no longer visible, the whole having 
become a raupo or phormium swamp. From this the transition to 
grassland through tussocks gaining a footing or to rain-forest by 
way of swamp (kahikatea) forest is in many cases only a matter of 
time. 
The blocking of watercourses with aquatic plants can soon convert 
grassland into a swamp. Even on shingly river-beds, swamps at 
various stages of growth may be observed, and toetoe-grass (Arundo 
conspicua), cabbage-trees (Cordyline australis), and New Zealand flax 
(Phormium tenax) break the monotony of the scene. 
Sinking of the land may bring about great changes in the plant- 
associations, and remains of plant-life in bogs or swamps can teach 
much as to recent changes in the land-surface. In the swamps of 
the Canterbury Plain in the neighbourhood of Christchurch con- 
siderable numbers of fallen trees are found, the remains evidently of 
a large semi-coastal forest, which must have been replaced by swamp 
during a sinking of the land, or the swamp may have ultimately been 
buried by shingle (fig. 79). So, too, on that narrow peninsula in the 
far north of Auckland is much kauri-gum to be met with in the bogs, 
a sure sign that the land stood considerably higher at the time it was 
occupied by kauri forest, since that tree is most rare in swamps. 
The changes noted above which are slowly taking place in swamps, 
owing to the gradual lessening in depth of the water, leads to the 
plants being arranged in more or less distinct belts or girdles, accord- 
ing to their being suited by structure or constitution to water of a 
certain depth, using the term “ girdle,’ since “belt” has already 
been selected as a name for the rings of vegetation encircling 
mountains. 
A journey on any of the New Zealand main railway-lines shows the 
traveller that swamps are even yet a very common feature of the 
landscape, for they can be recognized at a glance by the dense growth 
