Abstract/Summary:
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 dense.
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.