PDF - Wallace Online

244 TROPICAL NATUREand fillsurrounding trees, in which a few ultimately prevailup the space vacated by their predecessor. Yet beneath thissecond set of medium-sized forest trees there is often a thirdundergrowth of small trees, from six to ten feet high, of dwarfpalms, of tree-ferns, and of gigantic herbaceous ferns. Yetlower, on the surface of the ground itself, we find much variety.Sometimes the earth is completely bare, a mass of decayingleaves and twigs and fallen fruts. More frequently it iscovered with a dense carpet of selaginella or other lycopodiacese,and these sometimes give place to a variety of herbaceousplants, sometimes with pretty, but rarely with veryconspicuous flowers.Flowering Trunks and their Probable CauseAmong the minor but not unimportant peculiarities thatcharacterise these loftyforests is the curious way in whichmany of the smaller trees have their flowers situated on themain trunk or larger branches instead of on the upper partof the tree. The cacao-tree is a well-known example of thispeculiarity, which is not uncommon in tropical forests and;some of the smaller trunks are occasionally almost hidden bythe quantity of fruit produced on them. One of the mostbeautiful examples of this mode of flowering is a small treeof the genus Polyalthea, belonging to the family of thecustard-apples, not uncommon in the forests of north-westernBorneo. Its slender trunk, about fifteen or twenty feet high,was completely covered with star-shaped flowers, three inchesacross and of a rich orange-red colour, making the trees lookas if they had been artificially decorated with brilliant garlands.The recent discoveries as to the important part playedby insects in the fertilisation of flowers offers a very probableexplanation of this peculiarity. Bees and butterflies are thegreatest flower -haunters. The former love the sun and frequentopen grounds or the flowery tops of the lofty foresttrees fully exposed to the sun and air. The forest shades arefrequented by thousands of butterflies, but these mostly keepnear the ground, where they have a free passage among thetree-trunks and visit the flowering shrubs and herbaceousplants. To attract these it is necessary that flowers shouldbe low down and conspicuous. If they grew in the usual