124 NEW ZEALAND PLANTS. 
and from an excessive rainfall in a climate of the subantarctic type. 
Hence in Westland, Southland, and Stewart Island bogs are common. 
In the North Island, before the land was drained, there were many 
bogs on the Waikato Plain, where they originated in the great swamps 
as peat accumulated. Hollows, too, of the Auckland gumlands are 
occupied by bog, so that two distinct plant-formations exist on these 
rather barren areas side by side. In the montane and subalpine 
belts of the high mountains bogs are a well-marked feature, though 
from the scenic stand point of little interest (fig. 84). Between 
swamp and bog there are many transitions. True sphagnum “bog 
may form an “island” in raupo-phormium swamp, as in a virgin 
swamp near Levin (Wellington). There on the sphagnum the 
phormium is much more stunted than that in the swamp, and 
much browner, while species absent in the swamp are common— 
e.g., bracken-fern (Pteridiwm esculentum). 
Although a bog is a station of extreme wetness, for some reason 
not yet properly understood the bog-water is not relished by the 
plants, so that in a considerable number of cases their growth-forms 
are similar to those of plants living under the driest conditions. 
To use the scientific term, the bog is “ physiologically dry.” It is 
a case of “‘ Water, water, everywhere, nor any drop to drink.” The 
peat of bogs, too, is deficient in such compounds of nitrogen, 
potassium, and phosphorus as the plant can use—three essential 
requisites. 
Various theories have been put forth—some backed by experiment 
—to account for the physiological dryness of bogs. The following, 
amongst others, have been advanced as causes: (1) The presence of 
free humous acids in the soil; (2) the lowering of the water-table 
during summer and the drying of the superficial layers of peat ; 
(3) coldness of soil and evaporation from the leaves increased by 
drying winds and want of moisture in the air; (4) the low 
temperature of the soil and its lack of oxygen; (5) the poisonous 
nature of the peat itself. New Zealand experience shows that 
on a certain mountain-slope in the North- eastern Botanical 
District the only place where a koromiko (Veronica salicornioides) 
of the drought-tolerating whipcord form grew was where its 
roots could obtain the icy-cold water of a stream. Also, a 
sphagnum-cushion supports an assemblage of plants which are 
not nearly so strongly provided with drought-resisting structure 
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