NEPENTHES - inside of pitcher wall

The inner surface of the jug is arranged so that captured animals cannot normally escape from the trap. The upper part and here especially the back wall (closest to the attachment of the lid) is densely covered with two layers of wax scales, of which the upper scales are only attached by a thin stalk that breaks off at the slightest touch, i.e. that the substrate slips if an animal tries to climb the wall. Loose wax scales are found in many other plants, e.g. flower and fruit stalks, where the scales act as a defense against crawling insects that will seek food in flowers or fruits. However, the stalked type is only known from Nepenthes.

Scanning elektronmikroskop microscopy of Nepenthes x mixta

     In the upper part of the pitcher, there are modified and inactive “stomata” that have the guard cells oriented across the longitudinal axis of the pitcher. These “stomata” are obliquely sunk into the inner surface of the pitcher, so that the upper guard cell forms a half-roof that covers the slit. This prevents the guard cells from being used as a foothold. The lower guard cell looks like an ordinary epidermal cell, and the slit itself is closed and motionless. It is therefore not a question of functioning stomata, but possibly of a gland of unknown function or simply of a structure that evolution is in the process of ridding Nepenthes of, because its original function has become redundant. The rest of the pitcher’s inner wall is waxy, greasy and mirror-smooth, except where the digestive glands are located (see separate page).

H. S. Heide-Jørgensen, Dec. 2009. Translated Jan. 2024