200 A NATURALIST IN BORNEO 



species none of the leaves are abnormally developed, 

 but are rather fleshy, kidney-shaped organs, concave 

 on the under side, fitting very closely to the bark of the 

 tree on which the plant grows, so that the little hollow 

 spaces underneath them afford a shelter to the 

 adventitious roots which spring from a point near 

 the petiole, and push their way under the leaves. This 

 adaptation is undoubtedly for the purpose of protect- 

 ing the rootlets from excessive drought and heat, 

 whilst the rootlets can absorb any moisture that tran- 

 spires from the inner surface of the leaves when these 

 are heated by the sun. Very often ants and other 

 insects are found under the leaves, but they cannot be 

 regarded as special ant-shelters. Dischidia rafflesiana 

 has certain of the leaves, especially those growing on 

 the older part of the plant, modified to form long 

 urn-like pitchers with open mouths. The develop- 

 ment of the. pitcher has been followed out in detail, 

 and it is now known that it is formed not by the 

 growing together of the leaf-margins but by the bend- 

 ing of the apex of the leaf towards the base. This is 

 really brought about by the arrest of the apical growth 

 of the leaf ; a rapid growth of the central portion of 

 the leaf ensues, and so the apex is brought round 

 towards the leaf-stock or petiole, and a pitcher is the 

 result. The inner surface of this pitcher is the 

 morphological under surface of the leaf, and the apex 

 of the leaf is at a point in the margin of the pitcher 

 exactly opposite the insertion of the petiole. These 

 hollow pitchers are filled with adventitious rootlets, 

 with fragments of soil and leaf-detritus, and are usually 

 swarming with ants. As both outer and inner surfaces 

 of the pitchers are coated with wax they are obviously 



