it EQUATORIAL VEGETATION 267 
the numbers of suitable insects are totally inadequate to the 
fertilisation of the countless millions of forest trees over such 
vast areas as the equatorial zone presents, and that, in con- 
sequence, a large proportion of the species have become 
adapted either for self-fertilisation, or for cross-fertilisation by 
the agency of the wind. Were there not some such limita- 
tion as this, we should expect that the continued struggle for 
existence among the plants of the tropical forests would have 
led to the acquisition, by a much larger proportion of them, 
of so valuable a character as bright-coloured flowers, this 
being almost a necessary preliminary to a participation in the 
benefits which have been proved to arise from cross-fertilisa- 
tion by insect agency. 
Concluding Remarks on Tropical Vegetation 
In concluding this general sketch of the aspects of tropical 
vegetation, we will attempt briefly to summarise its main 
features. The primeval forests of the equatorial zone are 
grand and overwhelming by their vastness, and by the display 
of a force of development and vigour of growth rarely or 
never witnessed in temperate climates. Among their best 
distinguishing features are the variety of forms and species 
which everywhere meet and grow side by side, and the extent 
to which parasites, epiphytes, and creepers fill up every avail- 
able station with peculiar modes of life. If the traveller 
notices a particular species and wishes to find more like it, he 
may often turn his eyes in vain in every direction. Trees of 
varied forms, dimensions, and colours are around him, but he 
rarely sees any one of them repeated. Time after time he 
goes towards a tree which looks like the one he seeks, but 
a closer examination proves it to be distinct. He may at 
length, perhaps, meet with a second specimen half a mile off, 
or may fail altogether, till on another occasion he stumbles 
on one by accident. 
The absence of the gregarious or social habit, so general in 
the forests of extra-tropical countries, is probably dependent 
on the extreme equability and permanence of the climate. 
Atmospheric conditions are much more important to the 
growth of plants than any others. Their severest struggle 
for existence is against climate. As we approach towards 
