244 TROPICAL NATURE 



surrounding trees, in which a few ultimately prevail and fill 

 up the space vacated by their predecessor. Yet beneath this 

 second set of medium-sized forest trees there is often a third 

 undergrowth of small trees, from six to ten feet high, of dwarf 

 palms, of tree-ferns, and of gigantic herbaceous ferns. Yet 

 lower, on the surface of the ground itself, we find much variety. 

 Sometimes the earth is completely bare, a mass of decaying 

 leaves and twigs and fallen fruts. More frequently it is 

 covered with a dense carpet of selaginella or other lycopodi- 

 acese, and these sometimes give place to a variety of herba- 

 ceous plants, sometimes with pretty, but rarely with very 

 conspicuous flowers. 



Flowering Trunks and their Probable Cause 



Among the minor but not unimportant peculiarities that 

 characterise these lofty forests is the curious way in which 

 many of the smaller trees have their flowers situated on the 

 main trunk or larger branches instead of on the upper part 

 of the tree. The cacao-tree is a well-known example of this 

 peculiarity, which is not uncommon in tropical forests ; and 

 some of the smaller trunks are occasionally almost hidden by 

 the quantity of fruit produced on them. One of the most 

 beautiful examples of this mode of flowering is a small tree 

 of the genus Polyalthea, belonging to the family of the 

 custard-apples, not uncommon in the forests of north-western 

 Borneo. Its slender trunk, about fifteen or twenty feet high, 

 was completely covered with star-shaped flowers, three inches 

 across and of a rich orange-red colour, making the trees look 

 as if they had been artificially decorated with brilliant gar- 

 lands. The recent discoveries as to the important part played 

 by insects in the fertilisation of flowers offers a very probable 

 explanation of this peculiarity. Bees and butterflies are the 

 greatest flower -haunters. The former love the sun and fre- 

 quent open grounds or the flowery tops of the lofty forest 

 trees fully exposed to the sun and air. The forest shades are 

 frequented by thousands of butterflies, but these mostly keep 

 near the ground, where they have a free passage among the 

 tree-trunks and visit the flowering shrubs and herbaceous 

 plants. To attract these it is necessary that flowers should 

 be low down and conspicuous. If they grew in the usual 



