Abstract/Summary:
In some epidermal glandular structures the protective quality of the cuticular complex may be secondary to other qualities allowing secretory or absorptive processes to take place.
When the stem parasite Cuscuta attaches itself to the host, it produces an adhesive upper haustorium. In the adhesive zone the epidermis forms a glandular epithelium of unicellular hairs with folded distal ends. The cuticle of this epithelium is of the lamellate type. During the secretion of the binding substance the lamellae break up and move from the furrows of the folded hairtips towards the surface of the host epidermis. Here the cuticular material is reorganized often with the fragmented lamellae oriented perpendicular to the surface of the host. This orientation may facilitate secretion of enzymes to break down the epidermal wall of the host.
In a number of glands, especially hydathodes and digestive glands of carnivorous plants, the secretion through the cuticle proper is facilitated by gaps. Such gaps may mainly develop in the dendritic type of cuticle. In other glands the plasticity of the cuticle proper is remarkable. It works loose from the underlying wall layers and becomes extended as a balloon around one or more gland cells. In some cases the balloon bursts to release the secretions, in other cases the diffusive properties of the extended cuticle may change to facilitate a slow and steady release of secretory products. In the carnivorous plant Utricularia the balloon or velum of the pavement epithelium of the bladder threshold serves a mechanical purpose in making the entrance watertight.
A number of other specializations of the cuticle occur in the carnivorous plants in relation to perception of mechanical stimulation, capture processes, storage of the digestive fluid in leaf pitchers and absorption of digested products. As many as possible of these specializations will be exemplified in the lecture.