PDF - Wallace Online

266 TROPICAL NATUREleaves standing up like great candelabra. Sometimes theground is carpeted with large flowers, yellow, pink, or white,that have fallen from some invisible tree-top above ;or the airis filled with a delicious perfume, the source of which one seeksaround in vain, for the flowers that cause it are far overheadout of sight,lost in the great overshadowing crown of verdure."Although, as has been shown elsewhere, it may bedoubted whether light directly produces floral colour, therecan be no doubt that it is essential to the growth of vegetationand to the full development of foliage and of flowers.In the forests all trees, and shrubs, and creepers struggleupwards to the light, there to expand their blossoms andripen their fruit. Hence, perhaps, the abundance of climberswhich make use of their more sturdy companions to reachthis necessary of vegetable life. Yet even on the uppersurface of the forest, fully exposed to the light and heat ofthe tropical sun, there is no special development of colouredflowers. When from some elevated point you can gaze downupon an unbroken expanse of woody vegetation, it oftenhappens that not a single patch of bright colour can be discerned.At other times, and especially at the beginning ofthe dry season, you may behold scattered at wide intervalsover the mottled-green surface a few masses of yellow, white,pink, or more rarely of blue colour, indicating the position ofhandsome flowering trees.The well-established relation between coloured flowersand the need of insects to fertilise them may perhaps be connectedwith the comparative scarcity of the former in theequatorial forests. The various forms of life are linked togetherin such mutual dependence that no one can inordinatelyincrease without bringing about a corresponding increaseor diminution of other forms. The insects which are bestadapted to fertilise flowers cannot probably increase muchbeyond definite limits, because in doing so they would lead toa corresponding increase of insectivorous birds and otheranimals which would keep them down. The chief fertilisersbees and butterflies have enemies at every stage of theirgrowth, from the egg to the perfect insect, and their numbersare, therefore, limited by causes quite independent of thesupply of vegetable food. It may, therefore, be the case that