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.