268 TROPICAL NATURE II 
regions of polar cold or desert aridity the variety of groups 
and species regularly diminishes ; more and more are unable 
to sustain the extreme climatal conditions, till at last we find 
only a few specially organised forms which are able to main- 
tain their existence. In the extreme north, pine or birch 
trees—in the desert, a few palms and prickly shrubs or aro- 
matic herbs—alone survive. In the equable equatorial zone 
there is no such struggle against climate. Every form of 
vegetation has become alike adapted to its genial heat and 
ample moisture, which has probably changed little even 
throughout geological periods ; and the never ceasing struggle 
for existence between the various species in the same area has 
resulted in a nice balance of organic forces, which gives the 
advantage, now to one, now to another species, and prevents 
any one type of vegetation from monopolising territory to 
the exclusion of the rest. The same general causes have led 
to the filling up of every place in nature with some specially 
adapted form. Thus we find a forest of smaller trees adapted 
to grow in the shade of greater trees. Thus we find every 
tree supporting numerous other forms of vegetation, and some 
so crowded with epiphytes of various kinds that their forks 
and horizontal branches are veritable gardens. Creeping 
ferns and arums run up the smoothest trunks; an immense 
variety of climbers hang in tangled masses from the branches 
and mount over the highest tree-tops. Orchids, bromelias, 
arums, and ferns grow from every boss and crevice, and cover 
the fallen and decaying trunks with a graceful drapery. 
Even these parasites have their own parasitical growth, their 
leaves often supporting an abundance of minute creeping 
mosses and hepatice. But the uniformity of climate which 
has led to this rich luxuriance and endless variety of vegetation 
is also the cause of a monotony that in time becomes oppress- 
ive. To quote the words of Mr. Belt: “‘Unknown are the 
autumn tints, the bright browns and yellows of English woods ; 
much less the crimsons, purples, and yellows of Canada, where 
the dying foliage rivals, nay excels, the expiring dolphin in 
splendour. Unknown the cold sleep of winter ; unknown the 
lovely awakening of vegetation at the first gentle touch of 
spring. A ceaseless round of ever-active life weaves the 
fairest scenery of the tropics into one monotonous whole, of 
