5 
144 THE TERM ‘‘ EXTRA-TROPIOAL.” 
« EXTRA-TROPICAL”: THE TERM DEFINED. 
‘* Extra-tropical ’’ (sometimes shortened to y ex-tropic ’’) is here used, 
as employed in South Africa and Australia, to designate the parts of 
those continents lying outside the tropics. In other countries 1t 18 ap- 
plied to the zone between the tropics and the warm temperate: in Europe, 
the Mediterranean; in America, California and the southern States. In 
New Zealand the Auckland District and the coastal country as far as both 
sides of Cook Strait may be considered the extra-tropics, but there is no 
marked line of division. Kauri, Puriri, Celery-top, and other extra- 
tropical species disappear from the forest, but its character remains the 
same. Extra-tropical forests are generally sufficiently different in 
character from the forests on either the warm or the cold sides of them ; 
but that, owing to its long isolation and abundant moisture nearly every- 
where, is not the case in New Zealand, where the ‘‘ mixed forest,’’ a 
typical ex-tropic type of forest, extends with little change to the extreme 
south. 
“ Sub-tropical ’”’ is a loose and misleading term, there being generally 
a very marked difierence between the climate and vegetation of the 
tropics and the extra-tropics, especially in the forests. 
The extra-tropics, outside the dry and desert country, are charac- 
terized by a dryish atmosphere, bright sunshine (here is the maximum _ 
of summer insolation), and heavy rain at intervals. When this rain 1s 
enough to provide abundant subsoil moisture the conditions required 
for the most vigorous tree-growth are attained. Thus, it is in the extra- 
tropics that are found the world’s largest trees—the giant Sequoias of 
California, the giant Eucalypts of Australia, the world’s biggest timber- 
tree (the Kauri, of New Zealand), the big Yellow-wood of South Africa, 
and the long list of noble trees found in the Caucasus, the Himalayas, 
and Japan. Few tropical trees come near these in size, and fewer still 
among the trees of temperate or cold climates. 
New Zealand may have restricted mineral wealth and grass that is 
difficult to maintain, but it is in the right place on the world’s surface 
for the best tree-wealth. Of this tree-wealth the best now is in the 
northern or extra-tropical part—the most valuable species and the largest 
trees. 
