Cuticles, in the widest sense of the word, are found all over the
surface of higher plants but attain in thickness and complexity their
most advanced development on aerial primary stems, leaves and fruits.
On a genetic basis the morphology, including the ultrastructure of the
cuticular complex, varies between species as well as within species
and even within the same leaf depending on the epidermal cell type in
question. However, some variation due to environmental influence may
also be found.
Generally, going out from the inside, the outer epidermal wall consists
of a layered wall of polysaccharides, a pectic zone, the cuticular layer,
the cuticle proper, and an epicuticular wax layer. Ultrastructurally
the cuticle proper may be one of four types. a) The lamellate type,
composed of almost equally thick alternating cutin and wax lamellae;
this type may be subdivided in relation to the extension of the lamellae.
b) The dendritic type, where, more or less perpendicular to the surface,
thin branching strands of electron dense material traverse an otherwise
homogeneous and electron translucent matrix. c) The reticulate type,
where electron dense material appears in a reticulum embedded in a translucent
matrix. d) The homogeneous type, which appears more or less electron
The cuticular layer is even more variable. It may be absent or it may
form the bulk of the outer wall. Ultrastructurally it consists of an
anastomosed network of electron dense fibrillae, interpreted as pectins,
between which cutin and wax are deposited in highly variable quantities.
At the present state of knowledge it is not clear if this classification
of cuticles should be further graduated, or if the number of types should
be reduced since some of the types may be related only to certain steps
during cell wall differentiation, and some may merely be artefacts due
to incomplete fixation. However, considering the wide spectrum of functions
and the diversity of environmental conditions it is readily acceptable
that structurally different cuticle types have developed.