Cephalotus follicularis - Peristome
The peristome teeth seen from the inside of the pitcher. Short pointed hairs are abundant on the underside of the teeth.
Surface of peristome tooth with seven sunken nectaries.
Longitudinal section of nectary from a peristome tooth. E, endodermoid cell. K, cutinized cell wall. N, nucleus.
Two peristome teeth seen from the side.
The peristome forms a semicircle of the pitcher edge opposite the adhesion of the lid. The lid is supplied with up to 24 pointed and sickle-curved teeth, which direct their tips toward the pitcher lumen. However, small pitchers of young plants have much fewer teeth. The strongest teeth are placed in the middle of the peristome. Their surface is waxy and smooth but with numerous sunken nectaries. Fluid from the nectaries may float down the teeth and make them even smoother so the animals searching for nectar easily lose foothold and fall into the trap.
At left a longitudinal section are shown through a nectary from a peristome tooth. The nectary consists of up to 20 glandular cells, which all are derived from a single epidermal cell. Towards the sides, the nectary is incapsulated by cutinized cell walls. These walls are impermeable to liquid and ions. At the bottom, the nectary is limited by a smaller number of endodermoid cells, i.e. a band-shaped zone of the wall around the cell is cutinized (k in the Fig.). It means all transport into the nectary must occur through the living cytoplasm of the endodermoid cells and through plasmodesmata (see example) across the non-cutinized cell walls.
The endodermoid cells rest on some basal cells, which receive basic compounds for nectar production in the form of sucrose from the phloem of the vascular bundles. Inside the glandular cells, the sucrose undergoes a few chemical changes before it is secreted as nectar. Therefore, the main function of the glandular cells is to act as a pump station delivering energy for the secretion and the cells are well equipped with mitochondria. Simultaneously with pumping nectar across the cell membrane water is drawn into the outermost cell wall. It means the pressure increases and small channels open in the wall particularly in places where the cuticle is thin and where it therefore may burst more easily (the section has only hit such places peripherally, but see here). The strong cutinization of the endodermoid cells now obtain its most important function by preventing the nectar in following a concentration gradient back into the plant.