116 FORESTRY OF NORWAY... 
of the vegetation of the polar seas, and are particularly 
abundant-in the colder temperate zone. The green colour 
is characteristic of those alge which grow either in fresh 
water or in the shallower parts of the sea; the olive- 
coloured alga are most abundant between the tide-marks; 
while the red-coloured species occur chiefly in the deeper. 
and darker parts of the sea. 
‘ As regards perpendicular direction, Forbes remarks, that 
one great marine zone lies between high and low water- 
marks, and varies in species according to the kind of coast, 
but exhibits similar phenomena throughout the northern 
hemisphere. A second zone begins at low water-mark, and 
extends to a depth of from 7 to 15 fathoms. This is the 
region of the larger laminarias and other fuci. Marine 
vegetation, including the lower forms, extends to about 50. 
fathoms in the British seas, to 70, 80, or 100, in the Medi- 
terranean and the Algean sea, Ordinary alge, however, 
seem scarcely to exist below 50 fathoms, Diatomaceze 
exist in the deep abysses of the ocean and nullipora.and 
corallines increase as other alge diminish, until they 
characterise a zone of depth where they form the whole 
obvious vegetation. : : : OF F : 
‘The vertical range of terrestrial vegetation has also 
been divided into similar zones in altitude. The relation 
is called hypsometrical. As we ascend from the plain to 
the top of a mountain we pass through . different belts 
of plants, to such zones of elevation is of vegetation, 
the extent and variety of which differ in different 
countries. When Tournefort ascended Mount Ararat 
he was struck with the circumstance, that, as. he left 
the low ground at the base of the mountain, he passed 
through a series of belts, which reminded him of the 
countries he had passed through in travelling from the 
south to the north of Europe. At the base the flora was 
that of the west of Asia; as he ascended higher he 
reached the flora of the countries on the north of the 
Mediterranean, then that of northern Europe, and when 
he reached the summit he found the Lapland plants, 
